Chapter 15
Incidental Catch and Ecological Observations of Juvenile White Sharks, Carcharodon carcharias, in Western Baja California, Mexico Conservation Implications
Omar Santana-Morales Centro de Investigación Científica y de Educación Superior de Ensenada
Oscar Sosa-Nishizaki* Centro de Investigación Científica y de Educación Superior de Ensenada
Miguel A. Escobedo-Olvera Centro de Investigación Científica y de Educación Superior de Ensenada
Erick C. Oñate-González Centro de Investigación Científica y de Educación Superior de Ensenada
John B. O’Sullivan Monterey Bay Aquarium
Daniel Cartamil University of California, San Diego
ABSTRACT Between 1999 and 2010, we documented incidental catch of 111 juvenile White Sharks (Carcharodon carcharias) during surveys of the artisanal and commercial fisheries along the Pacific coast of Baja California, Mexico and opportunistically collected stomach samples. Sharks *
Corresponding author (
[email protected]). 187
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Global Perspectives on the Biology and Life History of the White Shark
ranged in size from 123 to 274 cm total length (TL). Most (79.8%) were young of the year (YOY) (≤175 cm TL), and the remainder were juvenile White Sharks (JWS) (>175–300 cm TL). Of the four documented fishing-gear types, bottom gillnets represented 74.7% of the catch, followed by drift gillnet (18.0%), artisanal seine net (4.5%), and surface longline (2.7%). Catch data indicate that the continental shelf is an important habitat for YOY and JWS in the region, with a possible core nursery area in Bahia Sebastian Vizcaino, where 66 YOY specimens were documented. Stomach content analysis for 14 JWS agree with previous studies showing that the species feeds primarily on bony fish and demersal elasmobranchs. National (NOM-059 and NOM-029) and international [Convention on International Trade of Endangered Species (CITES)] regulations ban the capture and trade of this species. However, monitoring of all White Shark catches is complicated by the remote nature of the fishing grounds, as well as socioeconomic considerations. Our data suggest that future White Shark conservation must include cooperative research and management plans between Mexico and the United States. INTRODUCTION White Sharks (Carcharodon carcharias) are taken as bycatch in several fisheries worldwide, with gear that includes longline, gillnet, trawl, handline, and rod-and-reel fisheries, and they are also opportunistically fished for jaws and other curios (Bruce, 2008). Although widely distributed, the White Shark is an apex predator with a naturally low abundance, low natural mortality, and low reproductive potential (Bruce, 2008). Because of these life-history characteristics and the perceived declining trend in some aggregation sites and sport fisheries (mainly in Australia and South Africa), the White Shark was listed as “vulnerable” by the International Union for the Conservation of Nature (Anonymous, 2002; Fergusson et al., 2005). In addition, this species was included in Appendix II of the 2004 CITES of fauna and flora to monitor trade in its products (fins, meat, jaws, and teeth) and ensure that such trade does not contribute further to its population decline (UNEPWCMC, 2010). An important component of conservation efforts is an analysis of White Shark habitat utilization, and the fisheries that may operate in those habitats, to assess the potential for fishery interactions and develop strategies to minimize fishery-induced mortality. Juvenile habitat may be particularly important in this regard, because low juvenile natural mortality could make fishing mortality a more significant factor in population dynamics (Kinney and Simpendorfer, 2008). Thus, restricted fishing in juvenile habitats may be warranted as a management tool for this species (Mollet and Cailliet, 2002). However, the distribution of juvenile White Sharks (JWS) is not as well known as that of adults. Electronic tagging studies in the eastern Pacific have shown that juveniles occur mainly in nearshore waters (Dewar et al., 2004; Weng et al., 2007b; Chapters 14, 16, and 28, this book), whereas adults show a seasonal affinity for both nearshore and pelagic habitats, including deep sea habitats, and exhibit wide-ranging travels (Boustany et al., 2002; Weng et al., 2007a; Domeier and Nasby-Lucas, 2008; Jorgensen et al., 2010; Chapters 11 and 16, this book). In the northeastern Pacific, JWS of
