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Hydrobiologia (2008) 601:137–141 DOI 10.1007/s10750-007-9260-5

INTERNATIONAL PIKE SYMPOSIUM

Current and future directions for pike ecology and management: a summary and synthesis P. Anders Nilsson Æ Christian Skov Æ John M. Farrell

Ó Springer Science+Business Media B.V. 2008

The pike (Esox lucius L.) is an exceptionally wellstudied species of fish. Its biology, ecology and management have been targeted in numerous studies during several decades (e.g. Crossman & Casselman, 1987; Raat, 1988; Craig, 1996 and references therein). Being a northern hemisphere circumpolar species, pike is the subject of research in many countries and cultures. A multitude of approaches to pike research have accumulated in the literature over the years. We do not seek to unify the body of international pike research, but rather advocate the

Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species P. A. Nilsson Limnology, Lund University, Ecology Building, 223 62 Lund, Sweden C. Skov Department of Inland Fisheries, Danish Institute for Fisheries Research, Technical University of Denmark, Vejlsøvej 39, 8600 Silkeborg, Denmark J. M. Farrell (&) Department of Environmental and Forest Biology, State University of New York, College of Environmental Science and Forestry, 241 Illick Hall, 1 Forestry Drive, Syracuse, NY 13210, USA e-mail: [email protected]

diversity of approaches to further the comprehension of the species and its interactions. Open communication channels between researchers from different countries or fields of pike research are of utmost importance for the facilitation and progression of pike research. This purpose was intended and served at the ‘‘International Pike symposium: Merging Knowledge of Ecology, Biology and Management for a Circumpolar Species’’, held at the 136th annual meeting of the American Fisheries Society in Lake Placid 2006. The objective of the symposium, ‘‘to create and facilitate information exchanges regarding northern pike biology and management across political and geographic boundaries’’, was certainly met by the participants who represented five countries in Europe (Denmark, Germany, Hungary, Sweden and UK), two provinces in Canada and six states from the east to west coast of the US in North America. The 28 presentations (Table 1) and two panel discussions during the symposium covered a wide variety of topics encompassing ecology, biology and management of pike. In the current contribution, we extract views and themes from the symposium in an attempt to summarise where pike research is at present, with reflections on where it may take us. We approach this intricate task by outlining the symposium communications on the ecology and management issues around the pike, some of which are published in this special issue of Hydrobiologia.

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Table 1 Authors and titles of presentations (in alphabetical order) at the International pike symposium held at the 136th Annual Meeting of the American Fisheries Society on September 14–15, 2006 at Lake Placid, New York, USA Robert Arlinghaus, Michael Raghib-Moreno & Ulf Dieckmann, Recreational angling-induced evolutionary changes in sizeselectively exploited pike populations. John Armstrong, Liam Simms & Martyn Lucas, Phenotypic flexibility in metabolic rate of pike. Jakob Brodersen, Lynn Nilsson & Anders Nilsson, Food choice and development of juvenile pike in different habitats within a lake. John Casselman, Long-term northern pike recruitment dynamics: effects of water level, temperature, impoundment, and possible adaptation. John Cooper, Robert G. Werner, Jerry Mead, & John M. Farrell, Coexistence of northern pike and muskellunge during early life and the implications of habitat change. Julie Cunningham, History of northern pike in California. John Craig, The role of pike in structuring fish communities. James Diana, The history and philosophy of management for northern pike in Michigan. John Farrell, Lars Rudstam, John Cooper & Robert G. Werner, Physiological ecology of Age-0 esocids: laboratory measurements, model development, and field comparisons. Ryan Fitzpatrick & Dana L. Winkelman, Identifying sources of northern pike recruitment in the Yampa River using otolith elemental signatures. Lene Jacobsen, Christian Skov, Soren Berg & Anders Koed, Migration pattern of northern pike in brackish waters of southeast Denmark. Thomas Klefoth & Robert Arlinghaus, Do pike modify behaviour in response to human predation risk in an experimental catch-andrelease lake fishery? Carolyn M. Knight, Rodolphe E. Gozlan, Martyn C. Lucas, Does size matter? Population structure and spawning strategy in pike. Balazs Kucska, T. Mu¨ller & M Bercse´nyi, New results in intensive rearing of northern pike. Terry L. Margenau & Steven P. AveLallemant, Management of northern pike in Wisconsin—the people’s fish. Jerry Mead, John Farrell, and Brent Murry, Simulating the response of YOY northern pike production to water level management in the Upper St. Lawrence River. Marc Minglebier, Phillip Brodreau, & Jean Morin. A dynamic field model developed in a large river to predict northern pike spawning habitat from migration to hatching. Thomas Mosindy, The response of northern pike to a walleye population collapse in Shoal Lake, Ontario. Brent Murry, John Farrell, Kim Schulz & Mark Teece, Effect of maternal size and condition on the variation in egg nutrient content and larval success in northern pike. Anders Nilsson, Northern pike interference: levels and effects. Edmund Pert, Managing Pike in California: Lessons learned and current plans. Rodney B. Pierce and Cynthia M. Tomcko, Density of northern pike populations in relation to basin-scale characteristics of lakes. Rodney B. Pierce and Cynthia M. Tomcko, Production dynamics of northern pike. Rodney B. Pierce, Oviduct Insertion of Radio Transmitters - A new means for locating northern pike spawning habitat. Tamas Szabo, New method to improve the quality of northern pike (Esox lucius) eggs obtained by hormonally induced ovulation Christian Skov, Do pike really suffer in poor visibility? Ian J. Winfield, J. Ben James & Janice M. Fletcher, Northern pike in a warming lake: population dynamics from 1944 to 2005 in Windermere, U.K. Paul Venturelli & William M. Tonn, Diet and growth of pike after introduction into a fishless lake: early consequences for persisting in disturbance-prone lakes.

Ecology of pike One of the questions arising during a panel discussion at the symposium was ‘‘how many species of pike are there’’? Any seasoned interest in pike should of course lead to the conclusion that there is only one taxonomical species of pike, but the question was

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nevertheless valid considering the surprising variation in observations and findings among the international pike researchers. There was broad agreement that pike should not be viewed as a behaviourally, ecologically or physiologically uniform and static species. Pike are found in a variety of habitats, foraging on almost whatever prey is at hand,

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coping with a great range of variation in temperature regimes and their populations appear in many densities and size compositions. Moreover, there is an astonishing diversity of individual pike characters within populations. As pike grow, a broad range of sizes of these predators exists, each with different predator behaviours and specializations through ontogeny. Individual behavioural strategies may also vary within size classes, as, for instance, spatial behaviour and foraging tactics can be markedly different between similar-sized individuals. Furthermore, an individual strategy is rarely fixed, and individual behavioural tactics may change with environmental conditions and prey abundance or composition in a highly plastic and opportunistic fashion. The phenotypic variation and plasticity is also accompanied by a substantial prerequisite for local adaptation, further enforcing the view of pike as very far from a phenotypic unity. The pike’s character diversity and propensity for plasticity and adaptation, and the resulting potential for phenotypic variation was well reflected in the symposium presentations. For instance, the scope of pike for standard metabolic rate is highly diverse and adaptive among individuals depending on food and activity, potentially explaining earlier among-study differences (John Armstrong). Further, as shown by Lene Jacobsen, pike populations in the Baltic show high individual variation in migration propensity between fresh and brackish waters, where some individuals migrate in association with the spawning period, while others do not. In a presentation on within-population and size-dependent variation in movement strategies and home-range sizes, Carolyn Knight indicated that slow-growing individuals, particularly males, made longer excursions over larger home-range sizes. Moreover, pike early-life growth patterns were shown, in a presentation by Jakob Brodersen, to be clearly influenced by individual opportunism according to habitat-specific seasonal progressions of food availability and composition. Early-life potential for success was demonstrated and significantly affected by maternal effects, where egg nutrient conditions varied among broods (Brent Murry). John Farrell developed an energetics model for growth during early life history of pike, and compared temperature and body size effects on consumption and respiration to its close relative, muskellunge (Esox masquinongy, Mitchell), but

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criticised its inability to represent individual variation. Egg, diet and larval development of pike and muskellunge were compared by John Cooper, who showed that under certain circumstances pike will hatch earlier in the season and grow faster than muskellunge, and that habitat change is promoting the species’ distributional overlap. Other presentations also made it clear that environmental variability, composition and change affect individual and population growth, where for instance water level, temperature and lake habitat and nutrient composition strongly affect pike recruitment and reproduction (John Casselman, Ian Winfield, John Cooper), and poor water visibility might have an unexpected positive effect on individual pike body condition in spite of the fact that pike are considered visually oriented predators (Christian Skov). Also, individual pike behaviour in terms of movement patterns and spatial distribution as well as foraging activity and prey preference reflect the propensity for plasticity and seems, at least partly, linked to intraspecific interactions and interference among pike individuals (Anders Nilsson). Clearly, the current scientific approaches to the understanding of pike ecology are highly influenced by the fascinating and diverse attributes of the study species.

Management of pike One of the remarkable twists to this symposium were presentations from managers from California and Colorado who viewed pike as an invasive species and highlighted their potential negative impact in systems following introduction. In all, four presentations looked at pike as an invasive, including introduction and success in a fishless lake (Paul Venturrelli), in California (Julie Cunningham and Ed Pert) where extreme lengths have been taken in attempts for eradication, and in Colorado where otolith microchemistry was used to understand recruitment patterns of invasive pike (Ryan Fitzpatrick). The ability of pike to reproduce and grow in these systems is astounding and threats on native fisheries resources and ecosystems are in the balance. In systems where pike are invasive and problematic, the emphasis of discussion was how to use what is known about this species to assist in the control of the spread of pike.

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In contrast to the above view, several papers focused on the decline of pike in their native ranges. This trend appears to be a fairly recent one and discussions focused on physiological tolerances and the effect of climate change and warming of aquatic habitats across the pike range. It was noted in one panel discussion that pike distribution is spreading north and it was predicted that difficulty in management would begin at the latitudinal fringes of their range and in waters prone to warming. This observation was supported by presented findings regarding the role of climate and prey base changes on pike in the south basin of Windemere in UK (Ian Winfield). A long-term perspective was also used by Thomas Mosindy to look at the pike population expansion following the collapse of a walleye population in a large Canadian lake. In addition to climatic forces, the role of flow regime interruption via dams and water levels management (John Casselman, John Cooper and Jerry Mead) on pike processes was a focus of several papers. Casselman developed pike recruitment indices from long-term data in the Lake Ontario-St. Lawrence River system and concluded changes in hydrologic and thermal regimes have a strong influence on their populations. Most waters today have water regulatory management in place and their influence on pike reproduction and critical habitat is a serious concern. Detailed modelling papers by Jerry Mead and Marc Mingelbier focused on pike habitat, water levels, and prediction of early life processes. Discussions of how to protect shorelines and restore habitat led to a consensus in the panel discussion that although technologies should be implemented, the focus should remain on habitat protection and restoration of natural flow processes to protect pike and the environment that sustains them. Several technological advances were presented, including a new method using oviduct insertion of miniature radio transmitters to locate spawning habitat of pike, as described by Rodney Pierce. In the area of culture, Tama´s Szabo´ presented a new method to improve pike culture through enhanced fertilization using hormone enhancement, and Balazs Kucska presented results on experiments designed to enhance pike pond production. The theme of the effects of exploitation and the need for pike to continue to provide recreational and commercial resources received a great deal of

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attention among symposium participants. During a panel discussion, a trend towards loss of large individuals in the recreational fishery was a concern among many participants and appears to be a consequence of overharvest in many waters. Several studies attempted to improve management by enhancing our understanding of variability and structure of pike populations among lake types. A presentation on habitat and ecological constraints for north-central Minnesota lakes indicated basin morphometry to have strong influences on pike population structure (Rodney Pierce). In these lakes it was also concluded by Pierce that angling selects the largest fish, a segment of the population with the lowest turnover and production. Reviews by James Diana showed how long-term management efforts have developed in Michigan, USA, and how population density and growth-based ecological groupings are used in angling management. Terry Margenau presented a historical review that chronicled a variety of management approaches used in Wisconsin, USA, including stocking efforts to sustain populations in developed areas. Both these papers indicated an urgent need to curb pike reproductive habitat loss. Changes in pike size structure due to angling likely have ecological consequences relative to population structuring. Stunted and overabundant populations are the norm in highly fished areas. One paper investigated the evolutionary consequences of harvest regimes (Robert Arlinghaus) with a life history modelling approach, where pike angling selection responses were predicted, suggesting a new and more complex view of angler effects on fish populations. Also, a study by Thomas Klefoth looked at anglerinduced behavioural responses by pike to disturbances, where catch and release angling was shown to greatly affect the spatial behaviour of pike individuals, with potential effects on interactions between pike and their prey.

Perspectives Pike have been studied from many scientific and management approaches for centuries, and the fascinating and intriguing pike will most certainly continue to attract the attention and interest of researchers in the future. The accumulated and expected knowledge on pike ecology, biology and

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management is considerable. However, comprehensive and general predictions of effects of pike on lake ecosystem composition and function and the role of exploitation are largely lacking, as pointed out in the presentation by John Craig and in one panel discussion of the symposium. Although having been the objective of many scientific projects through the years, we still cannot tell exactly how and by what mechanisms pike in general affect their prey and thereby trophic processes in their aquatic habitats. However, disappointing or discouraging this may be for managers and researchers, the prospect of achieving these generalizations is simultaneously a driving force and source of inspiration for pike researchers. Different pike populations rarely if ever have the same compositions and functions, and thereby do not affect their trophic systems in the same way, making studies of pike a line of inspiring challenges and mysteries. Specifically, we believe the pursuit of the explanations and mechanisms behind between-population discrepancies not only acts as an inspiration, but also holds a substantial key to the understanding of pike biology and ecology. Pike populations are made up of pike individuals, and the differences between population functions should be sought for in the astounding diversity of individual characteristics and variability. This diversity of individual characteristics and variability impedes simplified approaches to predictive and general population- or communitylevel models of effects on and of pike among aquatic ecosystems. It does, on the other hand, draw the attention to one of the themes dealt with during the symposium: it is crucial to evaluate and understand how and why individuals do what they do in order to comprehend how populations and communities work

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and interact. A thorough understanding of the mechanisms behind individual decisions and behaviours is necessary to predict how pike populations react to environmental variation, or how pike affect prey communities and trophic processes. Moreover, extrapolations from individuals to such higher-order processes are highly specific for spatially and temporally distinct events and populations, presenting a significant task for pike ecologists. Findings should, in order to enable reliable predictions of effects of pike in trophic systems, be evaluated alongside long-term data from both population- and ecosystem-level studies, as indicated and envisioned by Ian Winfield and John Craig during the symposium. Without the longer-term perspective and the bridging of order scales from individual to system levels, we may risk erroneous predictions and their subsequent social, economic and ecological consequences. Despite the striking challenges this approach introduces to the study and management of pike, the symposium leaves us with the notion that a major driving force behind the future progression of pike research is the splendid fascination arising from recognizing the multi-faceted attributes of the significant, circumpolar and captivating species.

References Craig, J. F., 1996. Pike: biology and exploitation. Chapman & Hall, London. Crossman, E. J. & J. M. Casselman, 1987. Annotated bibliography of the pike, Esox lucius (Osteichtyes, An: Salmoniformes) Royal Ontario Museum. Raat, A. J. P., 1988. Synopsis of the biological data on the northern pike, Esox lucius Linnaeus, 1758. FAO Fisheries Synopsis, No. 30, Rev. 2, 178 p.

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