ancient lineage through an unusual leptocephalus. (Greek for leaf head) ... ardize fishing opportunities for the silver king. Despite the ... stronger collaborations to learn the secrets of ..... A review of the records can give us a sense of how big ...
CHAPTER
15
Silver King A Most Perfect and Ancient Sport Fish The Biology, Ecology, Management of Megalops atlanticus—and its Precarious Future By Jerald S. Ault, Ph.D.
tlantic tarpon have reigned
A
Meisel’s Tales of Old Florida (1991),
supreme for more than a
wherein bouts with the silver king
century as one of the most
were immortalized in various
sought-after inshore game fishes.
writings:
The popularity of the “silver kings” soared when President Franklin D. Roosevelt battled them in 1937 off Port Aransas, Texas. But the excitement really began years earlier in south Florida and the Florida Keys through the exploits of Zane Grey, Charles F. Holder and a host of other legendary anglers. A biggame fish in every sense, tales of its pursuit and capture are wellchronicled in excellent books such as Grey’s Tales of Fishes (1919),
The man who has caught trout, black bass, or salmon, and has added to this the delight of shore fishing for tautog, bluefish, or striped bass, has many pleasant and exciting contests to remember; but if he should get fast to a tarpon all his other fishing experience— desperate as some of them may have seemed—will be eclipsed in a moment. —Charles F.W. Mielatz, “The Angler’s Battle Royal” (1903)
The thrill tarpon offered anglers was recognized early on by C.F. Holder (1903) who stated, “Texas should add the tarpon rampant to her escutcheon, as sooner or later the fame of this splendid fish and the remarkable fishing found along her shores will become one of the prime attractions of the region.”
Few species can match the tarpon’s brute strength, airborne acrobatics and tremendous stamina, or the hair-raising power surges that marks a quality fight. Blessed with superb
Holder’s The Big Game Fishes of the United States (1903), and Oppel and A
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Previous two pages and opposite: migrating tarpon in April 2008 at Bahia Honda, Florida.
T A R P O N
physical characteristics, these animals can resist the strongest currents with ease and attack hapless prey with impunity. Tarpon are an enigma. They offer a challenge to biologist and angler alike. Hooked up, you feel the unbridled survival instincts of one Earth’s oldest creatures, skills that have been honed over more than 100 million years of evolution and a range of severe climate changes. Innate morphological and behavioral characteristics have also allowed them to successfully elude the best natural predators. But the tarpon’s complex life history, biology and spatial distribution as it grows and ages makes scientific study difficult. Among perhaps the most primitive assemblages of living bony fishes (Family: Elopiformes), tarpon—along with bonefish, ladyfish and eels—exhibit an ancient lineage through an unusual leptocephalus (Greek for leaf head) larval stage. Life begins as schools of adult tarpon travel offshore, generally in spring and early summer, to broadcast their spawn into warm oceanic waters. Fertilized tarpon eggs hatch into a leptocephalus larvae after about 24 to 48 hours. Then the larvae lives and grows for the next 15 to 30 days in the plankton while drifting shoreward at the whim of wind, current and tide. Once inshore, metamorphosis occurs and the larvae transform into the familiar form of a tarpon that anglers recognize. The early juvenile life stages typically live in relatively anoxic freshwater swamps that form a barrier to aquatic predators and harbor few competitors. But the seascape has changed dramatically for tarpon during the last 50 years. This ancient warrior and ultimate sport fish is now on the ropes in many of the most prominent historical fishing locations. Tarpon populations have experienced precipitous declines in portions of their range along the U.S. Atlantic and Gulf of Mexico coasts. Port Aransas—the “tarpon capital of the world” for much of the early 20th century—for example, is now virtually devoid of the tarpon numbers that made it so famous. There is serious speculation concerning the root fishing and environmental causes for these declines, and to A
whether these could occur elsewhere and jeopardize fishing opportunities for the silver king. Despite the longstanding interest anglers have exhibited in the species, we have only recently begun to learn more about tarpon population dynamics and ecology, migrations and spawning areas in U.S. waters (i.e., Gulf of Mexico, Florida and southeastern United States) and the Caribbean Sea. In this chapter of A Passion for Tarpon, I’ll explain the natural scope, the life history and place in context the population biology of this ecologically valuable wild resource. I’ll discuss fishing impacts on this economically important resource. And I’ll discuss how better knowledge of the science by anglers is critical to sustaining our tarpon fisheries.
UNLOCKING THE SECRETS OF TARPON MIGRATIONS Anglers have long wondered where big tarpon come from and where they go. Do populations of the species migrate internationally? And why have tarpon populations declined or increased over years in different regions? These questions are fundamental to determining the unit stock appropriate for management that ensures sustainability of the fisheries. Unfortunately, but seemingly typical, much more is known scientifically about commercial food fishes than species less desirable for human consumption (e.g., sport fishes). The confluence of escalating economic importance, new technologies and pressing interests in conservation of the species have recently opened a window of opportunity for improved understanding of the connections between tarpon fisheries in U.S. waters and those of the Caribbean Sea. This all began some eight years ago, when International Game Fish Association Hall of Fame inductee Billy Pate, asked a relatively simple question at a Bonefish & Tarpon Trust (www.tarbone.org) board meeting, “Are our tarpon their tarpon?”
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A decade of studying migrating adult tarpon with innovative pop-up archival satellite transmitting tags has revealed that regional tarpon populations undergo extensive long-range seasonal migrations throughout the Gulf of Mexico, the southeastern Atlantic coast of the United States, and the Caribbean Sea—our tarpon are indeed everyone’s tarpon.
Billy had observed firsthand the slaughter of large mature tarpon in numerous Latin American countries by commercial and subsistence fisheries. He surmised that those impacts may have been responsible for the substantial declines of the tarpon fisheries observed off Port Aransas, Texas, decades ago, and more recently at Homosassa, Florida, where Billy pioneered tarpon fishing on fly. Billy’s question stimulated much discussion at a board meeting of the Bonefish & Tarpon Trust (BTT), of which I am a founding member. It directly resulted in angler-based support for a scientific quest to utilize new technologies and to develop stronger collaborations to learn the secrets of the population dynamics of migrating tarpon. Not long after that “tarpon fisheries
epiphany,” I met with a very senior fisheries research biologist at the National Oceanic and Atmospheric Administration to inform him of our interests in satellite-tagging tarpon to learn more about migrations and population connectivity. To my surprise, I was met abruptly with the prejudicial comment: “Oh, Jerry, don’t bother. We already know everything about them. It’s a states’ problem [meaning each U.S. state should have a separate management approach for tarpon].” He continued, “Besides, the federal government would never have any interest in tarpon management because we know that there is no international component to the stock.” I thought about his comments long and hard. On what basis he could have been so certain? I
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Conventional and pop-up archival (PAT) tag set-ups: (upper) conventional tag on applicator; (middle) PAT tag setup with ball-bearing leader attachment and titanium dart; (lower) close-up of PAT tag and sensors. Information on the fish’s whereabouts is tracked by satellite.
knew enough to realize there were little to no data available to make such a series of assertions. Today, as the result of ongoing and revealing scientific investigations into the long-range movements of tarpon, we know how wrong this person really was! But this “case closed,” know-it-all attitude is pervasive among many managers when it comes to recreational species that are generally not actively pursued by commercial fisheries. It is a principal reason that many recreational fisheries are in trouble today. To an alarming extent, it seems to typify the historic approach —more accurately, non-approach—to understanding and perpetuating marine recreational fisheries. If the particular fishery is catch-andrelease, this exacerbates the problem. It encourages an even deeper motivation for inaction and doing nothing. You can’t imagine how many times I’ve heard the comment from wellplaced fisheries managers, “Oh, Jerry, there’s no problem with that resource!” I usually respond quickly with something like “How do you know that?” The retort, of course, is A
invariably, “It’s catch-and-release, so everything is okay.” It’s a crying shame that much more is known scientifically about Atlantic cod and mullet, for example, than tarpon, simply because the former two species are—or once were—huge economically-important commercial fisheries. By comparison, other inshore game fish, magnificent but far less desirable for human consumption, have been egregiously ignored. But we persevered. Since those initial encounters and proclamations, unprecedented collaborations undertaken among scientists and anglers have spawned state-of-the-art techniques. Guided by biologists from the Bonefish & Tarpon Conservation Research Center at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, and fueled by funding sources such as BTT, research doors are opening wider. Perhaps the most unique innovation: spaceage pop-up archival transmitting (PAT) tags. They track tarpon migrations and evaluate habitat use along the way. The PATs cost $6,000 per unit and utilize satellite technology. Essentially, they are relatively small computerized sampling devices attached to the back of a tarpon via a titanium dart. A PAT contains electronic sensors. Every 10 seconds these sensors record the fish’s depth, light level, temperature and salinity of surrounding water. Unlike conventional anchor tags requiring the recapture of tagged fish, PATs can be pre-programmed to automatically release from the fish at a specific date and time (usually about six to eight months after deployment). At that moment, the tags “pop up” to the surface and transmit compressed versions of the stored information to a network of orbiting satellites. All the information is forwarded to our computers at the University of Miami’s tarpon conservation research laboratory for detailed analyses. While physical recoveries of deployed PAT tags aren’t necessary, when the tags can be found via ARGOS locator devices, it allows downloading of the entire data archive. A comparison of environ-
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mental data allows estimated locations of the and range of tarpon migration has revealed tagged fish along their migration routes. itself in a magnificent way. Funds for this tagging research have been More than 100 years ago, in 1903 Charles provided by anglers and funding partners from Holder speculated with remarkable accuracy on organizations principally led by BTT. Other con- tarpon migrations: tributors include the Sanctuary Friends Foundation of the Florida Keys, Tarpon Tomorrow, Texas The tarpon is a migratory fish, moving north over the Parks and Wildlife Department, Florida Fish vast area of the Gulf. One pronounced migration is and Wildlife Conservation Commission, Marine along the coast from Mexico reaching Louisiana; the Ventures Foundation, and the Texas Saltwaterother possibly passing up the Windward Islands, so Fisheries Enhancement reaching Key West or Association. Others vicinity, following up have contributed much the Keys to the Cape, time and resources to some following the the effort, notably Scott west and others the Holt at University of east coast. I infer this Texas Marine Science from the fact that if Institute, Tad Burke and the vast schools the Florida Keys Fishing moved north in the Guides Association, centre of the Gulf, Scott Alford and the they would have been Ta r p o n To m o r r o w noticed at the TortuTexas Pro-Am, Angel gas group, where, as Requejo and the Verstated, the fish is rare. Tagging the coastal giants: Researcher measuring tarpon for dorsal girth and fork length before applying the acruz Yacht Club, Lance Around Cuba and PAT tag to the fish and then releasing it. In the summer “Coon” Schoest in other islands some of 2009, a 98-pound tarpon tagged and released the Louisiana, Bruce Ungar tarpon are found all previous spring in the Florida Everglades traveled an and the Stuart Fishing the time, but they are astonishing 2,200 miles to the North Atlantic Ocean near where the H.M.S Titanic sunk! Club, Joe Mercurio and more plentiful in sumthe ProTarpon Tournamer at the Florida ment Series, Eduardo Points; schools have Perusquia and the Coatzacoalcos Yacht Club, been seen all winter between Key West and Cape Florida Sportsman magazine, Sport Fishing magaFlorida, particularly at Caesar’s Inlet. They appear in zine, and the Trinidad Tarpon Bash. February, increasing rapidly in numbers in March, We have been tagging tarpon with these April, and May, entering rivers and streams as the innovative archival transmitting devices tags Apalachicola, being seen eight miles from the mouth since 2001. Through 2009, some 139 PAT tags … have been deployed in Florida and the Florida The tarpon makes it appearance in Aransas Pass, Keys, Louisiana, Mexico, Texas, Alabama, GeorTexas, early in March of each year, coming from the gia, the Carolinas, Trinidad, British Virgin south. During the months of March, April, and May Islands and Angola, Africa. The results show they may be seen in schools of six to one hundred, that sexually mature tarpon—those at least 100 coming up the coast from the south. Reaching the pounds and greater than a five-and-a-half-foot deep waters of the Pass, they congregate in the gorge fork length—are the ones that migrate. The of the Pass for a while, as though to rest and feed, largest migrating tarpon are females. The rate and then pursue their journey north along the coast 265 SILVER KING
to Galveston, Sabine Pass, and other points. From the middle of April to the middle of May they do not appear to take the hook or bait; during this time they are congregated in large numbers in the shallow bays and flats and can be approached easily in a small boat without displaying any alarm, and no lure will tempt them to take a hook. Apparently this is their spawning season … About the first of December the tarpon disappear entirely from the Pass; I believe that they go south or seek the warmer waters of the Gulf.
Holder’s conjectures were supported, in general, by conventional tagging studies on tarpon in the intervening years, but these studies lacked the replication and biological-environmental details for fishery management to pay attention or to act.
GEOGRAPHIC DISTRIBUTION OF THE KING Tarpon are principally thought of as a coastaloriented species. They can reach a large size (to 300 pounds) and as adults are now known to be highly migratory. They are distributed on both sides of the tropical central Atlantic Ocean, generally from about 10°S to 35°N. In the western Atlantic, tarpon range along the Atlantic coast from Virginia to Florida, Bermuda, throughout the Gulf of Mexico, central America and the Antilles islands in the Caribbean Sea, and to northern South America to Brazil. They are infrequently observed as far south as Argentina and as far north as Nova Scotia. By and large, the current distribution of tarpon corresponds directly to that of tropical mangrove trees, particularly for the larval and juvenile life stages that are ultra-sensitive to water temperatures and food regimes. Tarpon range widely. The Atlantic species has been reported recently from the eastern Pacific Ocean, as far north as southern Costa Rica, a range expansion facilitated by the Panama Canal. A
In the eastern Atlantic Ocean, along the western coast of Africa, tarpon occur primarily from Angola in the south to Senegal in the north. Occasionally tarpon are seen in Portugal, the Azores and southern France to northern Spain. Astonishingly, a 151-centimeter fork-length specimen—59 inches long and about 72 pounds—was caught in Cork, Ireland, in 1981. (Note: all measurements of the length of a tarpon stated in this chapter are given as the exact length from the tip of a tarpon’s snout to fork in its tail—so-called “fork length” or FL). It is not clear whether this was an eastern Atlantic fish from Africa, or a western Atlantic (U.S. and Gulf of Mexico) fish that swam northeastward across the Atlantic Ocean. Adult tarpon roam freely throughout Gulf of Mexico and southeastern United States waters from April to November each year. The bulk of the tarpon population found in the eastern Gulf of Mexico in U.S. waters are centered seasonally, from April to November, in Florida. Mature fish migrate into Florida about mid-March to April. The “South Atlantic” group component then begins moving northward from Florida, through Georgia, onto the Carolinas in June, and then all the way to Virginia on the U.S. eastern seaboard by about August. These schools feed heavily on menhaden up and into the Chesapeake Bay, and then return southward along the coast beginning in late September. Most of the schools are through southern Florida by late November. Where they go from November to April is unclear. There is also an unquantified portion of this so-called “Gulf group” in the eastern Gulf, found in Whitewater Bay and Florida Bay, Everglades National Park, as early as February and March, and then in the Florida Keys in the early spring (mid-April through May). These schools then migrate northward as the waters warm, showing up in Boca Grande, Florida, en mass beginning each year in late May to early June. They continue northward past Tampa Bay and Homasassa, Florida, in late June and July. From
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there they continue onward from Florida to Alabama and the coastal waters of Mississippi and Louisiana and the mouth of the Mississippi River. It is highly likely that some proportion of these “eastern Gulf” fish mix with those tarpon of the “western Gulf” group that move north in the Gulf from Mexico through Texas. Tarpon are also seasonally abundant in the western Gulf of Mexico. In early May the very large fish—some exceeding 240 pounds—arrive in Veracruz, Mexico, from the Bay of Campeche. But by early June these fish are mostly gone. They migrate northward, moving through Texas and then to Louisiana, and by late July, are drawn to the biological riches contained in the plume of the Mississippi River. The extent of mixing of eastern and western Gulf groups and how these are connected to areas south of U.S. waters remains an important mystery central to improved understanding of tarpon population biology—and to the effective international management of sustainable tarpon fisheries in the western Atlantic Ocean. The connectivity of tarpon populations on either side of the Atlantic basin is also the subject of much speculation. Genetic studies have indicated potential differentiation between African tarpon and those from the western Atlantic Ocean, suggesting that gene flows may be low between east and west sides of the Atlantic. Some researchers, however, have found that African tarpon possess the most common western-Atlantic genes. In general, discrepancies between these studies may have been due to the genetic markers used. A fair amount of confusion on this topic still exists. One researcher has claimed, based on genetics analyses, that Costa Rican tarpon may be partially isolated from other Caribbean Sea populations. But on the face of it, this proposition really does not logically make sense, and has never been actively tested by scientific-based tagging studies utilizing fish from this area. Clearly, more research is required to make
definitive declarations. Among the western Atlantic groups, similar genetic diversity values were found, suggesting connectivity between these resources. When one views the outfall of the Congo River, whose salinity plume influences the north coast of South America by producing “retroflection eddies” between Venezuela and the Antilles Islands, it would seem to suggest two distinct possibilities. One, that tarpon larvae are advected (moved by ocean currents) across the ocean; or two, based on what we have learned from PAT-tagging, it won’t be surprising to find that adult tarpon could swim the distance between Africa and northern South America, using the rich biological production of the retroflection eddies to fuel the journey. The tarpon is habitually a wandering, predaceous fish. It preys voraciously upon mullet, menhaden, shrimp, crab, ribbonfish, sardines and small fry of a similar nature. Its powerful lashings devastate the schools, pursuing forage fishes up the rivers into bays and over the flats. In the past, Mexican tarpon were known to ascend the Panuco River, near Tampico, some 40 or 50 miles, and a small one was taken south of Veracruz in the Papaloapan River some 125 miles from the Gulf of Mexico. Tarpon have to act somewhat like salmon in the river systems of Nicaragua, to enable movement hundreds of miles upstream through rapids and falls into the fresh waters of the Rio San Juan. This is a substantial highvolume flow river that creates the natural border between Nicaragua and Costa Rica, and connecting Lake Nicaragua near Managua— the second largest freshwater lake in the world—with the Caribbean Sea. Tarpon comigrate with bull sharks up these riverine systems. The reasons for tarpon using these rivers are probably related to a dependable, seasonally available food source, which raises speculation about the historical and present use of other such river systems by tarpon throughout the broader Caribbean Sea, Gulf of Mexico, and southeastern United States.
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EXPLOITATION AND HUMAN IMPACTS Because of their large body size and relatively firm muscle mass, tarpon are highlyprized fish for consumption in certain locations for either subsistence or, in some cases, commercial exploitation. Generally, tarpon have not appealed to consumers as food fish in United States fish markets, and thus have not been the target of U.S. commercial fisheries. Unlike in the U.S., tarpon are highly esteemed for their food value by subsistence fisheries in many Latin America countries including Mexico, Belize, Honduras, Cuba, Puerto Rico, Nicaragua, Costa Rica, Colombia and Trinidad. Outside U.S. waters, sábalo—as tarpon are locally known in Latin America—face a gauntlet of gears and associated dangers posed by commercial and subsistence fisheries that line the migratory paths of these regal fishes. The most typical gears used are long lines and gill nets. The roe of large female tarpon is prized foodstuff in Mexico and other Latin America countries. Sábalo soup remains a popular traditional dish along the Caribbean coast of Columbia, contributing to localized stock declines. These declines may also be attributable to habitat destruction, with reports that tarpon were dynamited in Columbia for harvesting. Three metric tons of tarpon were produced by aquaculture in Columbia between 1985 and 1987, but this practice appears to have ceased. Tribal cultures along coastal Africa use tarpon as the centerpiece of wedding ceremonies. Mostly, though, the magnitude of tarpon-directed Third World subsistence and commercial fishing operations remain largely undocumented. In today’s world, legions of anglers revere tarpon as the ultimate catch-and-release sport fish. Taken in relatively shallow waters, tarpon at times eagerly attack natural baits, artificial lures and flies with ferocious intensity. When hooked they make strong runs and spectacular leaps as high as 10 to 15 feet, completely out A
of the water. Their large adult-body size, strenuous fighting characteristics, and striking silver flash hold tremendous appeal as a premium sport fish. But the dichotomy of uses between recreational and commercial/subsistence presents a particular dilemma for their management and sustainability. Tarpon fisheries in the United States have largely been recreationally-oriented, but the historical focus was more of a catch-and-hang-‘emup affair. Today, the majority of states in the U.S. fishery have moved predominately to a catchand-release ethic, although a few states still allow trophy kills and a few large kill tournaments still persist along with unrestricted take. In U.S. waters, tarpon are the focus of substantial, economically-important recreational fishery ranging seasonally from Texas to Virginia. Tarpon are the primary subject of a number of big-money seasonal recreational fishing tournaments throughout the region, especially in Florida, but also Louisiana and Texas. Anglers in Florida who wish to take, kill or possess a tarpon— generally for a trophy mount—must first purchase a “tarpon tag.” The cost of this permit has remained US$50 per fish since it was instated in 1989, and there is a daily two-fish limit per person. The number of tarpon tags issued to professional fishing guides may not exceed 1,250, however, and the total annual number of tags issued by the state may not exceed 2,500. Since this regulation was established, fewer than 100 tarpon have been harvested per year in Florida. Both juvenile and adult tarpon are targeted by recreational anglers in Florida. The state’s adult tarpon (≥100 pounds) fishery is seasonal; most of these tarpon are caught from May to July when the large, mature fish (>170 cm FL or 67 in and 120 pounds) annually migrate northward through state waters. Smaller, immature fish are caught year-round, particularly in southern Florida. Bill Curtis, a long-time tarpon guide extraordinaire, recognized for his experience and acu-
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Historical fishing ethic for tarpon circa early 1900s—and throughout much of the 20th century—was to hang ’em high to impress your friends. Tragically, when the celebration was over, many of these irreplaceable, decades-old spawners ended up in the town dump to rot.
men in south Florida and the Florida Keys, has been fishing the region since the 1930s. He and noted fishing legend Stu Apte have recently opined that tarpon populations in Florida and the Gulf of Mexico have declined more than 90 percent during the last 50 years. The giant schools that Bill and Stu remember as boys that were once regular occurrences are now relatively rare. This is the same reflection recanted by other knowledgeable folks, e.g. the Farley family, who remember the tremendous fishing in Port Aransas that marked the 1930s and 1940s. By the 1950s the schools had largely disappeared from Texas. Gone too are the halcyon days documented in writings of the late 1800s and early 1900s that describe “acres and acres” of mullet with waves of tarpon leap-frogging over one another to catch the terrified leaping mullet chronicled in Tales of Old Florida: When a school of tarpon comes up with a school of mullet, the big fish are so eager to get at their prey that the second rank will often leap clear over the advance line into the thick of the company of mullet,
laying about them right and left with their tails, and lashing the water into foam flecked with the blood of the small fry. The mullet, on his side, has been equipped with means of escape, for he is able to make jumps that are remarkable for a fish weighing, as he does, from two to three pounds. They spit through the air for fully twenty feet. The most remarkable exhibition of this that it ever was my fortune to witness took place in Biscayne Bay, near Miami [I believe this could have been in Bear Cut between Virginia Key and Key Biscayne where the Rosenstiel School now sits]. The school of mullet was fully an acre in extent. They went into the air in a mass, followed closely by tarpon. It was a wonderful sight, and meant a frightful mortality to the mullet, for the tarpon must have killed thousands of them. Some fishermen—the veterans, sometimes, but the new men always—are possessed with a wild desire to try and hook one when they see this preliminary performance. They may be seen frantically urging their boatman, first this way and then that, in the hope of cutting off a school in time to drag their bait before them, or to cast it among them. … As a result of this unseemly haste, it is not unusual to see an impatient fisherman hooked to a jewfish [now known as Goliath
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grouper], a follower of the tarpon, just at the time when the fish begin to feed and the propitious moment has arrived. I have seen the agony on his face while he tugged away at his jewfish, when the water all about was alive with tarpon, and a bait could not touch its surface before a fish would be there to take it. In fact, I have had the experience myself, and know the feeling. Now it would seem that a jewfish, weighing from one hundred to three hundred pounds, might furnish fairly good sport in itself. But it is not tarpon, and there is nothing more to say. —Charles F.W. Mielatz, “The Angler’s Battle Royal” (1903)
Not only are the great schools of tarpon and mullet that were once so common greatly reduced today, but the regional “jewfish” population is so depleted that it is now under a complete state and federal moratoria in U.S. waters. Causes for these observed declines are many. In addition to fishing and exploitation, other factors such as loss of critical juvenile habitats obliterated by coastal development, and loss of tarpon prey through overfishing, reductions in habitat quality and quantity, and declines in water quality. The reach of these systemic pressures is important to resource management and fishery sustainability. In Mexico, tarpon fisheries range from Tampico southward through the Bay of Campeche, around the Yucatán Peninsula and then southward to Belize. Mexico is home to several of the real granddaddies of tarpon tournaments, with the Veracruz Yacht Club in its 44th year, and the Coatzacolcos Yacht Club in its 55th year. These tournaments have historically been kill-oriented. New cars, abundant cash and other prizes have motivated anglers to bring their catches back to the dock to hang them for weighing and bragging rights. The residual impacts on the regional tarpon population of such negative behaviors are not clear, but I believe they clearly have direct impact on U.S. fisheries. I have personally observed more than six metric tons (>12,500 pounds) of very large tarpon killed at one single three-day recreational kill tournament at a single location, a coastal town, on the Gulf of Mexico. A
What this suggests to me is that, because of the highly migratory nature of the resource, it is highly vulnerable to considerable undocumented landings that may be significantly eroding the sustainability of home fisheries literally great distances away. Fishing lodges dedicated to tarpon sport fishing are found in choice locations just about everywhere the species ranges in western African and the Caribbean Sea; particularly in Belize, Honduras, Nicaragua, Costa Rica, Panama, Puerto Rico, Bahamas, Colombia, Venezuela, French Guyana, and south into Brazilian waters. But the most developed fisheries are in Florida and Costa Rica. In Florida, anglers spend hundreds of millions to billions of dollars each year to catch tarpon on rod and reel. Tarpon are singularly the most sought-after game fish off the Caribbean coast of Costa Rica. The potential impacts of directed-fishery catches, intensifying fishing effort, and insidious catch-and-release effects in the northern Caribbean region are largely unknown. What is known is that there has been substantial growth in technological capacity and potential fishing power of the fleets during these last several decades. In addition, virtually exponential increases in participants in the fisheries have been observed throughout the region. Unrestrained growth of human populations in the coastal zones has also accelerated habitat destruction, water-quality degradation, and disruption of prey-species dynamics. It has been noted that that post-release mortality is less for angled tarpon that have not been removed from the water and/or lifted up for photographs. In addition, aggressive angling techniques (e.g. use of heavy tackle) intended to shorten fight times may also help to substantially reduce release mortality because they reduce the build-up of lactic acid in the fish, reducing its vulnerability to predation by comigrating sharks after release. Recent studies have estimated catch-and-release mortality at about four percent, with three principal phases
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of stress to the fish: (1) capture—hooking, angling duration, water temperature, shark attacks; (2) handling—hook removal, air exposure, length of retention; and (3) release—revival and recovery, shark attacks. The impacts of catch-and-release fishing, while widely assumed to be negligible, remained largely unquantified for tarpon throughout its range. T h i s i m p o r ta n t q u e s t i o n m u s t s o o n b e addressed and quantified for fishery management because there is a large and growing number of participants in the fishery and seasonal catch-and-release tournaments in Florida, the southeastern U.S., Mexico, Trinidad, etc. Tragically, the true picture of the historical productivity—how good these fisheries really were—is now relegated to a collection of fading photographs. And paradoxically, as these tarpon fisheries were never really the focus of intense commercial fishing, the data fundamental to modern fishery stock assessments (catch, effort, size and age structure of the catches) and managing the resource in a sustainable way, were never collected. So for the most part, accounts of historical abundance of tarpon are found only in popular articles of the era, word of mouth or pure conjecture. The reality is that fishery catches and associated effort, the basis of estimating stock size and trends in abundance, have been poorly documented throughout the tarpon’s range. Lack of this essential information greatly hinders today’s assessment and management capabilities. One of the greatest challenges to fishery management that lies ahead concerns the sustainability of regional tarpon fisheries. With a catch-and-release ethic becoming more common, it may be that the impacts of recreational fishing on tarpon populations are minimal, but these need to be quantified. In general, rising exploitation pressures, rapid coastal shorelines along the migration routes, and significant environmental changes in coastal waters from rapidly growing human populations and climate change may threaten critical food supplies,
upsetting tenuous balances in the ecosystem. New information on migration, spawning areas, population dynamics and resource ecology is critically needed to support proactive fishery management strategies to conserve these precious resources. Unfortunately, the body of available scientific information lacks substantive data essential to predicting the future course of tarpon fisheries—imperative to making decisions concerning habitat preservation, stock management and conservation.
HOW BIG DO TARPON GET? Anglers are constantly in pursuit of record fish. A review of the records can give us a sense of how big tarpon might get. The International Game Fish Association (IGFA) database for tarpon registers the all-tackle world record at a weight of 286.9 pounds (130 kilograms). It is a record held jointly with a fish from Lake Maracaibo, Venezuela, in South America, caught in 1956, and Rubane, Guinea-Bissau, western Africa, captured on March 20, 2003. The Maracaibo monsters—the largest thought to have tipped the scales at 283.4 pounds—are probably phenomena of the past. This waterway is now dammed, likely severely compromising its ability to produce exceptionally large fish. The fish from Guinea-Bissau currently stands as the IGFA all-tackle world record. In recent years, many of the line-class records have been replaced by big fish taken off the central western coast of African, particularly in Sierra Leone, Gabon and Guinea-Bisseau. Tarpon larger than 300 pounds have been reported taken in artisanal fishermen’s nets off Africa! In the northern Caribbean, Gulf of Mexico and southeastern Atlantic, the majority of the IGFA saltwater and saltwater fly-rod records have come from Florida Bay and the Florida Keys (U.S. state and regional angling records for tarpon are displayed on the next page.), where angling for tarpon is seasonally intense. Interestingly, most of these state records have
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State recreational angling records for tarpon around the U.S. southeastern Atlantic and Gulf of Mexico coasts. State
Weight (lbs.) Date Caught
Angler
Florida
243.0
1975
Gus Bell
Georgia
161.0
July 1995
C. Edwards
South Carolina 200.0
September 2008
S.B. Kiser
North Carolina 193.3
September 2008
Malcolm Condie
Virginia
130.0
1975
Barry Truitt
Alabama
203.0
Unknown
Unknown
Mississippi
167.0
May 2001
K. Goodfellow
Louisiana
230.0
August 1993
Tom Gibson
Texas
210.7
October 2006
Jeremy Ebert
Mexico
245.0
May 2007
Torneo 42 de Veracruz
World Record
286.9
March 2003
Max Domecq
been taken during the last 15 years; I think this is largely due to better fishing technique and high-performance tackle (lines, reels and rods). The Florida Fish and Wildlife Conservation Commission (FWC) Saltwater Record Program shows that the Florida state record tarpon of 110.2 kilograms (243 pounds) was landed on conventional gear at Key West, Florida, on February 17, 1975. This catch record and those from the above table suggests that Florida may not be home to the biggest tarpon in recent times, even within the regional ecosystem. Fly-fishing records are largely from Florida—the bulk from the Florida Keys—but several important ones from Homosassa, including the largest taken on a fly rod (202.5 pounds), in 2001. A.J. McClane, in the 1974 edition of his Standard Fishing Encyclopedia, wrote, following Kaplan (1937) that an individual tarpon of 98 inches in fork length (249 centimeters) and 352 pounds (159.7 kilograms) was reported taken by a commercial net fisherman from the Hillsborough River Inlet, Florida, on August 6, 1912. However, this report as far as I can ascertain, was unverified. Much earlier, in 1903, Charles Holder suggested that tarpon may reach a length of seven or eight feet and a weight of 400 A
pounds, and stated that Evermann recorded a tarpon weighing 380 pounds that had been harpooned. But there is no substantive evidence that supports the presumption that a behemoth of this magnitude may have existed within the past 150 years. While record keeping for tarpon has been habitually poor, I do think that there is a distinct possibility that a 325-pound fish may be out there somewhere, possibly in Central to South American waters or on the shores of western Africa.
How Big Was That Tarpon You Caught? Because catch-and-release angling is rapidly becoming a dominant ethic in tarpon fishing— both for organized amateur and professional tournaments, and in the course of ordinary recreational angling—to reduce stress on angled fish, a convenient way to precisely estimate the weight of the fish from other body measurements has long been of interest. A popular weight estimation formula, developed by William H. Wood—a pioneer of tarpon fishing—presented in Heilner’s Salt Water Fishing (1945), has been widely used. But as I will point out here, this formulation provides a negatively biased estimate of the fish’s weight, i.e., it substantially underestimates the true weight of the tarpon. Thus, to eliminate this dilemma, here I provide a reliable new estimator for gauging the weight of the tarpon you catch. Wood’s general formula was developed by implicitly assuming that the body shape of a fish can be approximated by two wedges placed base to base, and that the specific gravity of a fish is approximately 1.15, so that about 25 cubic inches of fish weighs 28.75 of seawater, or about one pound. With a little algebraic manipulation, body weight is estimated by
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Here girth and fork length are measured in inches and weight in pounds. The formula has been broadly applied to a number of species such as striped bass, marlin, tuna, etc. I found that for tarpon the reality is that this formulation is negatively biased, meaning that it underestimates the weight of a tarpon by about -13 percent on average, with increasing error in the estimate with increased size of the tarpon. I endeavored to develop an empirical function that efficiently estimated tarpon weight. To do so, I took a very different tack than Wood and used modern multivariate statistical methods coupled with precise measurements of tarpon weight (W, in kilograms), fork length (FL, in centimeters) and dorsal girth (G, cm) that I obtained from several reliable sources: (1) scientific studies in Florida; (2) the IGFA world-record database on Atlantic tarpon; and (3) data originating from regional Mexican tarpon kill tournaments (e.g., Veracruz Yacht Club, Coatzacoalcos) held during
How much does that tarpon weigh? Estimates of tarpon weight as a function of fork length and dorsal girth. Fork length is from the tip of the lower jaw to the fork in the tail. Dorsal girth is the circumference around the tarpon just in front of the dorsal fin. Weight isopleths are in pounds. In the example shown on the chart: fork length = 83 inches; dorsal girth = 42 inches; weight = 210 pounds.
2000–2009, where the fish are brought to shore and accurately weighed and measured. These data were used to parameterize a log-linear version of a generalized multivariate linear statistical model (Ault 2008): Where is natural logarithm of weight of the i-th observation, is natural logarithm of fork length (FL), is natural logarithm of dorsal girth (G), are parameters to be estimated, and is the lognormal error term. Higher-order terms were ignored because partial F-tests revealed that their inclusion into the model did not significantly reduce the mean squared error. We took advantage of the high correlation between weight, fork length and girth to produce the model
which produces very accurate weight estimates, such that more than 95 percent of all predicted weights are within two percent of the tarpon’s true weight over the size range of 10 to 93 in fork length (25 to 235 cm FL, i.e., approximately 10 to 93 in FL). To convert the model estimated weights to kilograms from natural logarithmic units, first take the natural exponential function . The conversion from metric to English units is relatively straightforward. For example, a tarpon that is FL=83 inches (210.82 centimeters) and G=42 inches (106.68 cm) would weigh W=210.8 pounds (95.6 kilograms), where pounds (lbs)=2.204622622 kg. Note that for the sample dimensions given above, Wood’s formula would have produced an estimated weight of 183 pounds, an underestimate of more than 13 percent. For the ease of angler’s use of my formula, here I have provided a surface plot of tarpon
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weight (W) as a function of FL and G in English units (pounds and inches). These should help take the guesswork out of how big that tarpon you just caught really was and hopefully help fishermen be more truthful about their catches— as we know, a difficult line to toe! A funny and perhaps tragic story surfaced after the development of my new formula. It comes from Belize. A couple of anglers had caught what they believed to be a world record fish on a fly one bright day on the water. They used the Wood’s formula to estimate weight and decided that their large tarpon was under the record by a number of pounds. Upon arriving back at the lodge and reporting their catch, they were asked if they had used the new Ault formula for weight estimation. To their chagrin, the Ault formula showed that they had returned what would have been the new world record to the sea without properly documenting their catch!
HOW OLD IS THAT TARPON? The actual ages of tarpon at a particular size—while of immense interest to anglers and scientists—have been difficult statistics to obtain and insufficiently documented throughout the range of the species. The majority of what we know scientifically about tarpon population dynamics and demographics (agegrowth, survivorship and births) comes from the seminal research of Roy Crabtree in Florida. More recently, these data from the global database of research studies were consolidated in my book Biology and Management of the World Tarpon and Bonefish Fisheries (2008), with a particular focus on Florida, the Gulf of Mexico and Bay of Campeche, Mexico. Crabtree’s estimates of age and growth of tarpon—from young juveniles to large adults— comes principally from specimens taken in southern and east-central Florida (i.e., the Florida Keys, Boca Grande Pass, and Indian River Lagoon). The A
smallest fish in length samples (sex undetermined) was 2.6 inches, while the largest male was 67.3 inches and the largest female was 80.5 inches. The distribution of length samples was bimodal, containing many small and a few large fish. By and large, these data do not give a representative picture of how old and large a tarpon may get, because they were biased toward small fish, lacked fish in the range of 35.4 to 47.2 inches, and contained few fish longer than 68.9 inches. Much of this simply had to do with the availability of large fish, because Florida, as I mentioned previously, may not presently have the largest fish in the region. Tarpon exhibit sexually dimorphic growth (sexes grow at different rates), with females growing to significantly larger sizes than males. I fit lifetime von Bertalanffy age-at-length growth functions for males and females using otolithaged tarpon data from Roy Crabtree’s Florida study and applying nonlinear regression methods. Weight-at-age was determined by evaluating a von Bertalanffy equation at age with the allometric (different parts of the body grow at different rates) function for weight dependent on fork length fit to thousands of data points from Florida, the International Game Fish Association (IGFA) world records, and Mexico. Crabtree’s detailed study of south Florida tarpon estimated ages for male and female tarpon and concluded that the oldest two females aged in their samples were 55 years old, at lengths of 70.9 80.5 inches fork length (FL), while the oldest male was estimated at 44 years old at 67.3 inches long. But an important point to make is that these fish were nowhere near the maximum lengths reached by tarpon, when in fact, the world record tarpon caught by Max Domecq in 2003 in Guinea-Bissau exceeded 98.4 inches (250 centimeters) FL. This suggests the maximum age to which a tarpon can live has been grossly underestimated. Some insight into this problem has been given by radiometric analyses conducted on tarpon during the last decade. These studies have suggested that female tarpon longevity may exceed
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82 years! Similar analyses on the Florida fish aged by otoliths to be 55 years—could have in fact have exceeded 78 years—and a male estimated at 36 years could have been up to or exceeded 41 years. These studies have concluded that a female tarpon that in the past we would have estimated to be 50.6 years of age, may have exceeded 78 years. Another insight into the extended lifespan of the species comes from a captive tarpon—captured in the wild in 1935 at about 59.0 inches in length—held alive at the John G. Shedd Aquarium in Chicago. Sixty-three years later, in 1998, it jumped out of the holding tank and died. Based on its size at capture, this fish was likely at least 10 years old when first placed in the aquarium, strongly supporting the revised notion that maximum age of the species exceeds 70 years. Other obvious issues concerning age and growth include the fact that samples available for earlier studies in Florida were highly selective towards tarpon shorter than 150 centimeters or 59.1 inches. In contrast, extraordinarily large tarpon are captured seasonally in the tarpon tournaments held at Veracruz and Coatzacoalcos, Mexico. More than 60 percent of the Mexican tournament-caught fish for the period 2000–2009 were longer than 175 centimeters or 68.9 inches, whereas only 24 percent of the Florida recreational catch exceeded this length
What are the Biological Implications of These Findings? The dynamics of fishery resources are defined by a series of inter-related population processes. Maximum age observed in a population relates to the average expected lifetime survivorship, a function of all sources of natural mortality (i.e., predation, disease, cannibalism, etc.) that reduce the probability of living. This instantaneous rate of natural mortality for tarpon, in fact, defines the maximum age and—by what was presented above—the maximum
possible size. Natural mortality also defines the stock’s sensitivity to exploitation. In general, populations of fish that live a long time and grow large—such as tarpon—tend to be extremely sensitive to even very low exploitation pressures. Practically, this means that even small amounts of additional mortality (read: that arising from fishing impacts) results in dramatic declines in the population’s spawning biomass. Reductions in spawning biomass affects the amount of births and survivorship of small “recruits” that support the future fisheries. In situations where the stocks have been fished for some time, for a big-game fisher, this means the probability of seeing fish that attain these maximum sizes/ages is greatly reduced; thus the reproductive contribution from these “big mommas” is greatly diminished. This points out the need to ensure that mortality rates are kept relatively low so that good fishing days and access to large fish are available today and into the indefinite future.
THE AMAZING TARPON LIFE CYCLE Key life history and demographic data are needed to assess the risks of increasing and intensifying exploitation and environmental effects on tarpon fishery resources. Critical information underlying stock sensitivity to exploitation includes spawning stock biomass, stock and recruitment relationships, and the fecund potential of mature fish among other key aspects of population dynamics. Maturity and stock reproductive outputs are keystone population-dynamic variables of sustainability.
Maturity and Fecundity Tarpon lack external body characteristics that enable one to easily distinguish the sexes by eye. But tarpon are diecious (meaning the sexes are separate) and sex can be determined visually in mature specimens by internal
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inspection of the large white teste for males or an orange ovary for females. The gonad of a mature specimen is quite large, extending the entire length of the dorsal abdomen. In Florida, about 50 percent of male tarpon reach sexual maturity by 46.3 inches, and 50 percent of females are sexually mature by 50.6 inches. Male and female tarpon reach sexual maturity at approximately 13 years of age, but females attain a larger size at maturity due to their more rapid growth, and they ultimately achieve larger sizes. Crabtree thought that Costa Rican tarpon may reach sexual maturity at smaller sizes than those in Florida, although he noted that Florida fish were significantly larger than Costa Rican fish of similar age. Notably, his Florida sampling was selectively biased because fish were obtained primarily from tournaments and taxidermists, and thus selectively harvested for their larger sizes (at age). Tarpon in Brazil attain sexual maturity at 37.4 and 49.2 inches FL for males and females, respectively. Fecundity (amount of yolked eggs, or oocytes, a female of a given size produces) of Florida tarpon was estimated gravimetrically and found to be positively correlated with body weight; ranging between 4.5 to 20.7 million eggs per fish, a range that encompasses Babcock’s (1951) estimate of 12,201,984 eggs for a 142-pound 80-inch female tarpon. Minimum fecundity is 1,081,330 oocytes per female. While maximum fecundity was estimated at more than 20 million oocytes per fish, these estimates were not made on the largest fish in the population, so that maximum fecundity may be much greater for an older and larger tarpon. The high fecundity per female, however, reflects the uncertainty of survivorship in the sea. Each female produces millions of eggs, yet sustainability of the A
population at current levels requires that two fish must survive from each male-female spawning event to reach sexual maturity and repeat the cycle.
A handful of year-old and younger juvenile tarpon. Inland freshwater outflow, healthy estuaries and intact networks of coastal mangrove forests provide critical nursery habitats for the growing fish.
Tarpon Spawning: Where Life Begins The timing and locations of tarpon spawning have generally been inferred either from larval distribution patterns in the sea or the timing of maturity states observed in the gonads of mature adults. By all accounts, tarpon are oceanic spawners. Eggs are fertilized and life begins in the deep ocean, off the continental shelf. Planktonic leptocephalus larvae of tarpon are widely distributed and common in major western Atlantic Ocean currents. The one- to two-month phase of larval development occurs up to 250 kilometers offshore in warm, clear, high-salinity waters. The number of regional spawning sites, as well as the geographical extent of tarpon larval dispersal is presently unknown. Local oceanic eddies
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and gyres may entrain pelagic larvae stages and contribute to partial isolation of tarpon populations. But little is known about this earliest part of tarpon life history, partially because fertilized tarpon eggs have never been observed in situ and the specific locations where tarpon spawn have never been identified. The general impression of these locations has been somewhat confirmed around Florida by sampling of the upper near-surface of offshore waters to observe larval distribution patterns. The location of spawning areas represents a significant gap in our understanding of larval production and subsequent population recruitment of tarpon. Adults have been observed in large groups. Schools of gravid tarpon migrate from nearshore staging areas to form large pre-spawning aggregations approximately two to five kilometers offshore that may “daisy chain”—consisting of milling tarpon oriented in a similar direction and swimming in apparent circles—presumably before moving offshore to spawn. Mature tarpon migrate into Florida inshore waters from late February through early May each year to vigorously feed on energy-rich blue crabs, shrimp, mullet, ladyfish, etc., to build up the quality of eggs and sperm in their gonads before moving offshore for spawning. In southern Florida, tarpon have been observed days prior to the new or full moon in groups of several males surrounding one larger female, with the males bumping the female’s vents in attempts to stimulate egg release. This may represent pre-mating behavior. The exact timing, cues, and locations of tarpon spawning have not been described, although gonadal development and spawning may be triggered by lunar-tidal (or solunar) cycles. New data from our satellite-tracked PAT tagging program suggests that tarpon
The complex and remarkable tarpon life cycle begins with oceanic spawning: (upper) leptocephalus larvae; (middle) late-stage pelagic larvae; and, (lower) mature adult.
exhibit extremely deep-diving behaviors (to 475 feet) a few days before new and full moons, which we speculate facilitates extrusion of eggs and sperm from the ripe gonads of spawning tarpon. Indirect evidence of the timing of spawning comes from observations of partially spent females with ovaries containing what are k n ow n a s “ p o s t - ova r i a n fo l l i c l e s ” a n d
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“advanced vitellogenic oocytes,” observed in both Florida and Costa Rican waters. A “gonadosomatic index” (GSI) is used by biologists to visually determine whether male or female tarpon are ready to spawn. A GSI increases as the gonad fills with developed eggs (yolk filled egg with complete chorion) or sperm, and peaks in Florida for both male and female tarpon during May. Spent (spawned-out) females make up less than 25 percent of the catch from May through July, but more than 90 percent of the catch in August. This strongly suggests that Florida tarpon spawn from April to July, and by August most fish are either spent or recovering. Interestingly, by July these mature fish have left Florida waters and migrated northward to feed in the forage-rich waters of the south Atlantic or the northern Gulf of Mexico. Direct evidence of tarpon spawning comes from the capture of leptocephalus larvae in oceanic surface waters over depths of 90 to 1,400 meters, with sea surface temperatures of 27 to 30° Celcius and salinities of about 36 parts per thousand (pure seawater). Tarpon eggs hatch in about 24 to 48 hours after fertilization. Tarpon size (length) at hatching is at about 0.1 inch, and a 0.2-inch larva was collected that retained a portion of its yolk sac. Larval collections have indicated that tarpon in Florida waters spawn offshore from May through August, with some spawning occurring perhaps to October. But larval tarpon have also been collected off North Carolina—an indication that tarpon spawning may also occur along the U.S. south Atlantic coast from Florida to Cape Hatteras. Alternatively, this may reflect northward advection from Florida spawning grounds via Gulf Stream currents during the 15 to 27 day (mean 20 days) larval stage duration. Notably, tarpon larvae have been found present in the Gulf Stream as late as November, although the location where these may have been spawned is unknown. Leptocephalus larvae have extremely high growth rates, yet may remain in the plankton for about a month before undergoing metamorA
phosis into their juvenile form. Otoliths of tarpon leptocephali collected from south Florida found that their ages ranged from two to 25 days for sizes ranging from 0.22 to 0.96 inches, respectively. Tarpon may be batch spawners (i.e., multiple spawns of an individual in a year). Costa Rican tarpon have been suggested to spawn yearround as reproductively active females were observed in all months. Gonads of tarpon caught off the northeast coast of Brazil suggest that reproduction probably occurs from October to January, while in Puerto Rico tarpon may spawn be year-round, but with peaks in March– May and July–September. Larvae are ultimately transported inshore where metamorphic juveniles are typically found in bays and coastal waters. Tarpon larvae do not move inshore until they undergo metamorphosis to the juvenile stage—a critical period influencing whether the pelagic larvae successfully transit to demersal habitats. During this period of metamorphosis the transparent leptocephali shrink from approximately 2.8 to 1.3 centimeters, perhaps in response to signals associated with inshore waters such as reduced salinity or turbidity. Once metamorphosis is complete, positive growth begins again. Back-calculation of hatching dates from the otoliths of young tarpon for tarpon in south Florida suggests it coincides with the June–August period. Recruitment—survival of metamorphic tarpon larvae from oceanic environs to inshore settlement as a recognizable juvenile tarpon—is highest from July–October, corresponding with the summer hurricane season. Summer tropical storms, hurricanes and associated flooding from storm surge may push metamorphic tarpon into interior streams and pools where the growth into the juvenile stage may be triggered by contact with a freshwater environment. The biophysical processes that interact to transport and ultimately deliver pelagic leptocephalus larvae inshore to juvenile habitats are complex, including significant advection by wind-
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induced currents associated with hurricanes. Size at recruitment to the population is 2.3 to 3.0 centimeters, which corresponds to age of recruitment of 25 to 31 days, respectively. Recruited juvenile specimens in Georgia have been found as small as 1.96 centimeters, and provided the following weight-length equation for tarpon ranging from 19.6 to 273.5 millimeters. Once inshore metamorphic larvae-juveniles appear to thrive in anoxic freshwater swamps where they live for the first one to two years of life, gorging on prey and being relatively immune to piscatorial predation, but keeping a watchful eye on wading and diving birds such as herons, egrets and cormorants.
Where are the Nurseries? Juvenile tarpon occur widely, but prefer a relatively warm estuarine or mangrove environment. They feed at or near the surface and readily capture insects that fall into the water. Small juveniles are restricted to the salt marshes and shallow mangrove-lined estuaries and stagnant pools of varying salinity where predator pressure is low and food supply high, such as the Everglades and the Big Cypress Swamp in south Florida. As facultative airbreathers (able to breathe air but not restricted to doing so), tarpon can tolerate harsh habitats characterized by anoxia, periods of extremely shallow water, and low oxygen and high hydrogen sulfide concentrations. Young-of-year (YOY) tarpon have been reported from as far north as North Carolina, but also Georgia, Florida, Mississippi and Texas, including inland reservoirs (via introductions), the Caribbean islands (e.g., Puerto Rico, U.S. Virgin Islands), and Central America. Generally, water temperatures below 10°C (50 ° F) are lethal to tarpon, which helps to explain their constrained northward distribution. Episodic kills of juvenile tarpon during cold winters are common in central and southern Florida, Texas, and northern Mexico in
areas where young fish lack access to deeper, warmer waters. Juvenile tarpon have been seen in Mississippi during the past few years, presumably deposited inshore in swamps during the extremely intensive hurricane seasons in 2004 and 2005 that included the monster tropical cyclones or hurricanes, Katrina and Rita. New data have even shown recruitment of small juvenile tarpon to Texas estuarine waters (William Dailey, personal communication). It is interesting to speculate as to how and when these young-of-the-year juveniles might ultimately contribute to the regional migratory group dynamics. Late juvenile tarpon depend on deep-water habitats such as canals and sloughs for emigration to coastal bays. Juveniles have been found to inhabit mud flats in Puerto Rico during times when connections exist among mud flats and adjacent lagoons, June through February. Storms may flush the juveniles into new habitats, providing them with additional food resources. Emigration from juvenile habitats may be mediated by increasing food requirements. While adult tarpon are common in Costa Rica, Nicaragua and Panama, juvenile tarpon are considered rare to almost absent in these areas.
Vital Feeding and Nursery Habitats Juvenile tarpon biology presents an enigma. It should be considered a top priority to determine the locations of essential nursery habitats for this species. Loss of nursery habitat is a significant concern for conservation of coastal species and it can undermine even the most restrictive management strategies to sustain adult stocks. Quantifying the extent of available nursery habitat supporting tarpon populations, along with the extent of spatial variability in their contribution to adult recruitment, would greatly support conservation efforts for this species. But a host of population biology questions remain. For example, what other biological and physical processes (e.g., hurricanes) link to habitats and their variability and
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regulate tarpon population abundance? Why do tarpon recruit to the exploited phase—the fishery—so late in life (i.e., at the size/age of sexual maturity) in the Florida Keys? Where are they before they arrive on the fishing grounds, i.e., what are the essential habitat(s) for immature tarpon? Otolith chemistry analyses may hold great potential in these investigations.
WHAT EXACTLY IS A “RESIDENT” FISH? Tarpon have been suggested to have resident and migratory or mixed populations. We believe these perceived differences are due to life stage. Immature tarpon don’t appear to migrate great distances per se. On the other hand, mature adult tarpon (longer than 60 inches or 150 centimeters) are primarily coastal fishes inhabiting nearshore waters and bays over a wide range of salinities (fresh to hypersaline) and temperatures (17 to 36°C). These relatively large fish can appear tens to hundreds of kilometers offshore; they are fully capable of migrating thousands of kilometers. During these offshore migrations they appear to prefer the 26°C isotherm. For the most part, those fishes that have been described as “resident” have been assumed by observers to stay in a general area and not move. By and large, this movement (or lack of) has not really been quantified, but I believe these fish to be immature tarpon less than the minimum size/age of sexual reproduction. Recall from above that I said these were fish about 46.3 inches in length for a male and 50.6 inches for a female. That’s a pretty big tarpon by most standards. I think people have confused these ontogenetic behaviors because a full-migrating tarpon is likely to be one greater than 110 pounds and five feet in length. So when people say tarpon are available all year round at specific locations in south Florida, for example, they usually mean small immature tarpon. A
TARPON AS BOTH PREDATOR AND PREY The tarpon’s superior mouth and large proportioned jaw allows it to capture food (normally whole prey items) from below via suction, particularly with a well-lighted background. Like most large marine fishes, the diet of the tarpon changes according to life stage. There is disagreement over leptocephalus larvae food habits and requirements; some reports conclude that they do not feed, while others suggest that first feeding larvae consume protozoans, rotifers, larvacean houses and fecal pellets. Juvenile tarpon are crepuscular, normally feeding first at sunset and then into the night if sufficient light is present. Generally characterized, the diet of juvenile tarpon is “carnivorous, but predominantly piscivorous.” Among juvenile tarpon there is a strong preference for small (0.6- to 3.0mm) cyclopoid copepods and fishes (73 percent and 22 percent, respectively). The remaining five percent of their diet consists of mosquito larvae, ostracods and small shrimp, which fluctuate seasonally with bursts in production. Shore birds, ospreys and eagles are the principal predators of juvenile tarpon. The surfacerolling habits of tarpon make them excellent targets for fish-eating birds. As tarpon grow and age the predator field changes. The size of prey consumed by tarpon increases proportional to their size. As a tarpon grows, fishes such as mullets (Mugil spp.), mollies and killifishes (Poecilia spp. and Gambusia affinis) become primary prey items. Adult tarpon (longer than 50 inches) feed on mullet, menhaden, blue crab, silversides, marine catfish, shrimp (pink shrimp in Florida, brown and white shrimp in the northern Gulf and Texas), ribbonfish (e.g., off Veracruz in the spring) and menhaden, among other species. Sharks, particularly great hammerhead (Sphyrna mokarran) and bull (Carcharhinus leucas),
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Timeless predator and prey: Tarpon feast on small baitfish such as mullet, while the tarpon chasing mullet are themselves pursued as prey by large sharks.
are known predators of adult tarpon, especially those that have been injured through hooking or releasing by anglers. We have noted these attacks to be especially pronounced on migrating fish that seem to be traveling in a virtual biological soup of predators and prey—baitfish, kingfish, tarpon, sharks—and marine mammals such as dolphin. Studies of feeding habits have identified the primary prey items for all life stages of tarpon. Continuing research should further assess the status of these prey species populations, the impacts of directed harvest on these pray species, and define trophodynamic links between predator and prey stocks. Bottom-up forcing in these food webs may determine productivity and community dynamics. Therefore, anthropogenic nutrient inputs, pollution and habitat destruction in coastal waters could potentially influence stock dynamics of prey and predators. An integrated-systems approach to these scientific investigations would be a critically needed shift towards an ecosystem-based perspective in management of these fisheries.
A TITANIC TARPON In 2009, a tagged tarpon, T-118, made the most incredible journey that we have recorded since we began satellite-tagging tarpon in 2001, one of 139 silver kings. When satellite tag T-118 began transmitting data on September 15, 2009, it had traveled more than 2,200 miles from where we originally attached it to a 98-pound tarpon caught on fly aboard Bob Stearns’s boat six months earlier in Whitewater Bay, Florida. This was likely the greatest distance ever covered by a tagged tarpon. T-118 began transmitting data precisely on schedule, six months after the catch. At the time, it was located well into the North Atlantic (near 40.5 degrees north and 54.5 degrees west), some 800 miles east of Cape Cod and only 250 miles southwest of the location where the Titanic sank almost 100 years ago. Now the question begs: How did it get there? And did the tag remain on the tarpon throughout the entire six months—or did it pop off at an earlier date and drift the remaining distance?
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From the data we recovered by satellite— including temperature, depth, light levels and salinity—we are certain that the tag was attached to the tarpon in mid-August when the fish was some 1,200 miles north of its tagging location in the coastal waters of southern Virginia near the Chesapeake Bay, not an unusual destination for some of these coastal wanderers. Not enough information and data exist, however, to explain exactly what happened after that. Unfortunately, T-118 has not yet been physically recovered. Considering its location in the northern reaches of a huge ocean, it may never be found. If that’s the case, much of the data permanently stored in memory will remain unavailable. T-118 transmitted for 10 days before its batteries ran out. That’s usually enough time for recovery by a search party, had it washed up on a beach. That obviously did not happen in this case (although some tags are eventually recovered and returned by beachcombers long after battery failure). After leaving Virginia, T-118 traveled at least another 1,000 miles eastward before it began uploading to the satellite. Perhaps not ironically, this is the same route followed by the warm current of the Gulf Stream—and its temperature in the mid-70s is well within a tarpon’s comfort zone. Our experience shows that PATs have proven that tarpon are indeed incredible long-distance travelers, and it is entirely possible that this fish went the distance. It might well have been under way to some unknown destination when the PAT finally popped off. (After all, folks are still scratching their heads about how the 72pound tarpon caught near Cork, Ireland, in the mid-1980s got there). PATs are tough, durable instruments, and we would not be surprised if T-118 does turn up on some European shore years from now. Until then, we’ll just have to guess as to what exactly happened. A
SOLVING THE MIGRATORY PUZZLE We now know that tarpon frequently travel hundreds to thousands of miles between seasonal spawning and feeding sites, sometimes in time periods as short as two months. For example, tarpon tagged in the southern Bay of Campeche, Mexico, in May have reached Louisiana and Mississippi waters by July and August; tarpon tagged in the Florida Keys in late May have reached the Chesapeake Bay by late July; and, tarpon tagged in Trinidad have ventured north of Martinique in the Windward Antilles Islands. Migrating tarpon typically arrive in the lower Florida Keys in mid-April, but this is highly regulated by water temperature. We suspect they are coming from the Caribbean Sea (Cuba, Yucatan, Belize, Honduras, Nicaragua, and Costa Rica), a question that forms the next critical frontier for our tagging research. When the tarpon are in the Keys they are feeding on mullet, shrimp and ladyfish, but particularly focus on blue crabs at night. Interestingly enough, the timing of their arrival corresponds to the out migrations of mature and gravid female blue crabs from the coastal bays and rivers to the ocean to spawn. The crabs are energy-rich, egg-laden morsels consumed by tarpon in mass quantities to build their own gonads just prior to spawning and to prepare for the migrations ahead. Tarpon typically leave the Keys when water temperatures exceed their preference. We find that typically late May to the middle of June. They are at St. Lucie Inlet by late June, moving northward on the Atlantic coast, and pulling out of Boca Grande Pass about the same time to the end of June. Tarpon tagged in south Florida and the Keys in April and May have migrated to Chesapeake Bay—and others to the Mississippi River—by July and August. Both of the latter groups presumably are searching oiland-protein-rich menhaden stocks to rebuild
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the gonads after late-spring to early-summer spawning. This prepares their bodies for the long return migrations ahead, as the various connection points relate to seasonally available, energy-rich food resources. With the tarpon’s propensity for international travel and long lives (80 and more years), they are especially susceptible to even low levels of exploitation. Tarpon migration distances can also be impressive, with surprisingly large distances of up to 50 miles covered per day. Therefore, extractions from the populations in Mexico, the Caribbean or Central America may directly impact U.S. tarpon populations. This downturn in tarpon numbers could have a huge negative economic impact in the U.S., as recreational fishing in Florida alone has surpassed the economic impact of that state’s citrus industry. Trinidad, the Dominican Republic and even Cuba share tarpon migrations with U.S. tarpon. An area of historical importance is Port Aransas. Historical data indicates that tarpon fishing was excellent along that portion of the Texas coast until the early 1960s. While southof-the-border commercial fishing for tarpon likely was the most insidious culprit for the fishery’s tragic decline, other factors such as water diversions, the shrimp industry and other impacts may have destroyed habitat and impacted juvenile tarpon. Add to that coastal development, the oil trade and commercial over-fishing, and it’s not hard to see how tarpon populations off Port Aransas—and anywhere—can be swiftly devastated.
A MAGICAL TEMPERATURE BAND Our PAT-tagging research has shown that migrating tarpon have an innate desire for water temperatures of 26° C (about 79°F). Tarpon seek this almost magical temperature band. They can suddenly materialize, seemingly overnight, in good habitats with food in this attractive water temperature. This figure 26°C
is also, surprisingly enough, the lower-bound temperature that tropical storm forecasters use to predict hurricane formation and generation. The temperature preferences of tarpon might suggest that tarpon may be one of the first and most prominent species to be affected by climate changes. How tarpon know where and when to locate such specific temperatures is quite another mystery. Undoubtedly, it’s a physical signal dictating when and where to spawn, and what types of food may be available for consumption along their annual migration routes. It’s not that temperature provides a specific limit per se, as tarpon can be found in waters as warm as 90° F. They also often make seasonal feeding sorties into very warm waters pursuing oil-rich prey such as menhaden, an extremely important food for silver kings. This magical temperature band has undoubtedly been imprinted into the tarpon’s genetic makeup. Tarpon exceeding 100 pounds are wellknown shallow-water inhabitants, especially in the Florida Keys and Caribbean. PAT tagging has shown that migrating tarpon are deepwater fish, too. Tarpon spend a lot of time in depths of 30 to 100 feet—we have documented impressive dives of greater than 450 feet. Their deepest dives usually occur at night. Some of the deepest-diving tarpon have been documented during migrations north from Mexico, during presumed spawning off Florida, and also fish from Trinidad crossing between islands in the Antilles chain. We think that most deep dives relate to spawning activities, but perhaps it’s instead for safety or a reaction to currents or prey abundance. Migrating tarpon also appear to follow welldefined deep-water paths. We documented offshore tarpon up to 50 to 100 miles apart rising and diving synchronously in the water column, which may indicate some bizarre natural order to their behaviors. The more information collected, the more questions arise—it’s like a giant, never-ending
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Above: Migrating tarpon reliably follow a temperature band of 79°Fahrenheit and can appear overnight like magic. This shows seasonal migrations (April to October) from 2001–2009 determined by University of Miami scientists using PAT-tag technologies. The white wedge shown between Cuba and the Yucatan represents the suspected northern boundary to seasonal migratory
jigsaw puzzle. Nonetheless, a critical scientific mission is being pursued to ensure sustained regional fisheries for the valuable and powerful silver king.
SHARED REGIONAL POPULATIONS A host of regional locales in the Gulf of Mexico and northern Caribbean Sea tout tarponangling opportunities as a means of attracting traveling sportsmen and other tourists. Few data are currently available to quantify their economic significance to regional communities, the size of these charter fleets, or their impacts on local stocks. What is known is that in the United States alone, tarpon sport fishing conA
areas for Atlantic tarpon during November to March. Right: Twelve monthly snapshots of regional sea surface temperatures for 2008 from Advanced Very High Resolution Radiometer (AVHRR) satellite sensors for the Caribbean Sea, Gulf of Mexico and southeastern United States.
tributes more than $6 billion annually to the regional economies of coastal southeastern United States and Gulf of Mexico—providing a livelihood to tens of thousands of Americans from Virginia to Texas. Although primarily a catch-and-release fishery in U.S. waters, sustainable tarpon populations are under threat from numerous sources including: (1) losses of critical natal habitat; (2) unnecessary harvests in certain states due to lack of regulations; and (3) commercial and subsistence harvests by long-lines and gill nets in Mexico, Cuba and the broader Caribbean. Evidence of non-sustainable U.S. tarpon fisheries already exists. As we have seen in the stark example of Port Aransas, once known as the “Tarpon Capital of the World” and host to presidents and potentates
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for its exceptional tarpon fishing through the 1950s, the fishery has declined so greatly that today the catch of a single tarpon warrants special mention. Our satellite-based tagging research has shown that tarpon undergo extensive long-range migrations throughout the Gulf of Mexico, southeastern Atlantic U.S. coast (seasonally as far north as Virginia), and Caribbean Sea. This means that all these tarpon fisheries rely on a single, shared regional population. Thus a sustainable future requires an integrated regional, national and international management strategy. Regulations in many U.S. states and neighboring countries are either nonexistent, or not adequate to sustain tarpon population levels. To protect these vital fisheries and their associated economies, Atlantic tarpon, the silver king of legend and lore, must be declared a game fish at the federal level. This action is necessary to conserve tarpon for the recreational, economic and environmental benefit of present and future generations. Tarpon are prized saltwater fish that can live in excess of 80 years and grow to well over 250 pounds, making them especially susceptible to overfishing. Formal gamefish status would spur states and countries to collaborate on the enactment of integrated regulations to protect tarpon fisheries, and allow negotiations to begin to ensure tarpon receive sufficient regional protection. Gamefish status for tarpon would further efforts to curb overfishing, and advance cooperative conservation based on sound science, in collaboration with state, territorial and local governments, the private sector, and others as appropriate. Finally, gamefish status for tarpon would also support the federal government’s new Ocean Action Plan. Because tarpon live in coastal wetlands and estuaries as juveniles, and nearshore and coastal oceanic habitats as adults, they are ideal indicators of coastal ocean health and the effects of climate change. Declaration of tarpon as a game fish will also underscore our commitment as a people to conserving the nation’s fragile natural resources. It A
would encourage—and provide a measure for— cooperative conservation between federal and state agencies. This is vital to ensure sustainable fisheries. Tarpon are valued for different reasons in different countries and by different cultures. This reality requires a unique blend of extensive international cooperation between anglers, guides, scientists and fishery management agencies to ensure their sustainability.
HELP US HELP TARPON To become involved in this new and exciting conservation adventure, you can “adopt a tarpon” by donating the cost of one or more satellite PAT tags and even joining us on an expedition to observe tag deployment. All donations will go directly to the purchase, testing, programming, deployment and recovery of the tags. Donations involving sponsorships of tags are handled by Bonefish & Tarpon Trust for the Center for Tarpon and Bonefish Conservation Research at the University of Miami. The Trust provides the UM Center a dollar-for-dollar match of your donation. All donors receive a handsome commemorative plaque and a letter documenting their tax-deductible gift. In addition, participants receive timely updates of research results on www.tarponresearch.com. Jerald S. Ault, Ph.D., is a professor of marine biology and fisheries at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science and lives on Key Biscayne, Florida. Dr. Ault is an internationally-renowned fisheries scientist who has published more than 90 peerreviewed scientific papers as well as some 200 more book chapters, technical articles and computer software on the biology, modeling, assessment and management of marine fisheries, particularly tropical coral-reef ecosystems. He is a Fellow of the American Institute of Fisheries Research Biologists, founding and executive committee member of the Bonefish & Tarpon Trust and editor of the book Biology and Management of the World Tarpon and Bonefish Fisheries by CRC/Taylor & Francis (2008).
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Ned Johnson with a fine lower Keys tarpon.
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