Spatial Ecology of Juvenile Lemon Sharks (Negaprion Brevirostris) in Tidal Creeks and Coastal Waters of Eleuthera, the Bahamas
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Environ Biol Fish DOI 10.1007/s10641-010-9693-y Spatial ecology of juvenile lemon sharks (Negaprion brevirostris) in tidal creeks and coastal waters of Eleuthera, The Bahamas Karen J. Murchie & Emily Schwager & Steven J. Cooke & Andy J. Danylchuk & Sascha E. Danylchuk & Tony L. Goldberg & Cory D. Suski & David P. Philipp Received: 3 August 2009 /Accepted: 27 June 2010 # Springer Science+Business Media B.V. 2010 Abstract Fisheries exploitation and habitat alteration Bahamas. Eleven juvenile lemon sharks (766± are threatening lemon shark (Negaprion bevirostris) 127 mm total length; mean±SD) were captured from populations because they use nearshore regions as various tidal creeks within the 23 km study area and nursery sites. As such, there is a need for information were surgically implanted with acoustic transmitters. on the spatial ecology of juvenile lemon sharks to A series of 27 hydrophone receivers acted as a identify critical habitats that require protection, as passive monitoring array to detect tagged individuals well as to understand their basic ecology. The purpose as they moved among habitats. Findings suggest that of this study was to determine the habitat preferences juvenile lemon sharks tagged in this study prefer and movement patterns of juvenile lemon sharks shallow water habitats within tidal creeks, and along a sub-section of coastline characterized by typically display high site fidelity with occasional coastal flats and tidal creeks of Eleuthera, The forays to alternate habitats or creeks. In fact, more K. J. Murchie : E. Schwager : S. J. Cooke : A. J. Danylchuk A. J. Danylchuk Fish Ecology and Conservation Physiology Laboratory, Department of Natural Resources Conservation, Department of Biology, Carleton University, University of Massachusetts Amherst, 1125 Colonel By Drive, 160 Holdsworth Way, Ottawa, Ontario K1S 5B6, Canada Amherst, MA 01003-9285, USA T. L. Goldberg : D. P. Philipp Illinois Natural History Survey, * : : : K. J. Murchie ( :) S. J. Cooke :A. J. Danylchuk: Institute for Natural Resource Sustainability, S. E. Danylchuk T. L. Goldberg C. D. Suski 1816 S. Oak Street, D. P. Philipp Champaign, IL 61820, USA Flats Ecology and Conservation Program, Cape Eleuthera Institute, T. L. Goldberg Eleuthera, The Bahamas c/o Cape Eleuthera Institute, Pathobiological Sciences, School of Veterinary Medicine, 498 SW 34th St, University of Wisconsin, Ft. Lauderdale, FL 33315, USA 1656 Linden Drive, e-mail: [email protected] Madison, WI 53706, USA C. D. Suski : D. P. Philipp S. J. Cooke Department of Natural Resources and Environmental Institute of Environmental Science, Carleton University, Sciences, University of Illinois at Urbana-Champaign, 1125 Colonel By Drive, 1102 S. Goodwin Ave., Ottawa, Ontario K1S 5B6, Canada Urbana, IL 61801, USA Environ Biol Fish than 90% of tagged lemon sharks had the greatest nearshore areas (Compagno 1984). Neonates and percentage of detections located at a receiver at or juvenile lemon sharks are restricted to an area of close to the location where they were tagged. There about 6–8km2 during the first few years of their life, was no evidence of differences in diel or seasonal with their territory gradually increasing to 300 km2 as movement and habitat use. Knowledge gained from it nears maturity (Gruber 1982). Adults expand their this study will be useful for directing future conser- activity space to include deeper offshore waters, yet vation and management strategies including coastal return to the coastal zone for the birth of their young development plans and marine protected areas. (Gruber 1982). The early life history and spatial ecology of juvenile lemon sharks are better known Keywords Lemon shark . Acoustic telemetry. than arguably any other shark species as a result of Site fidelity. Nursery area extensive work by Samuel Gruber and colleagues on a population at Bimini, The Bahamas (reviewed in Sundström et al. 2001). Bimini is a cluster of islands Introduction that enclose a shallow lagoon habitat which provides nursery grounds for juvenile lemon sharks (Correia et Globally, sharks and other apex predatory fish species al. 1995). The collective research has revealed that are in decline (Baum et al. 2003; Christensen et al. juvenile lemon sharks in the Bimini lagoon demon- 2003; Baum and Myers 2004), largely as a result of life strate high site fidelity [i.e., temporal attachment of an history characteristics that make them vulnerable to individual to a space in its habitat (Carraro and fisheries exploitation (i.e., slow growth, late maturity Glastone 2006) and limited home ranges (Morrissey and low fecundity; Walker 1998; Kroese and Sauer and Gruber 1993a, b; Gruber et al. 2001)]. Given this 1998; Stevens et al. 2000). However, some shark information, the degradation of coastal habitats has species are also facing threats from habitat alteration the potential to reduce the ability of these sharks to associated with coastal development (Manire and meet their requirements for growth and survival. Gruber 1990; Camhi et al. 1998). Species which use The increase in tourism development in the nearshore regions as nursery sites (e.g., Castro 1993) Bahamas and other countries in the Caribbean is are particularly at risk as these habitats are essential for changing the connectivity and structure of coastal the growth and survival of juveniles and therefore the habitats (Buchan 2000). At present, 60% of The persistence of the population. Therefore, there is a need Bahamas gross domestic product of 2.7 billion is for information on the habitat selection and movement based on tourism (Buchan 2000). Therefore, devel- patterns of juvenile sharks in nursery habitats to opment of resorts, beaches, and leisure areas on identify critical areas that require protection, as well coastal zones is in high demand. As development as to understand their basic ecology if shark stocks are increases and coastal habitats become destroyed or to be managed successfully (Merson and Pratt 2001). fragmented, further information regarding lemon To date, there have been reasonably few studies on the shark movement and activities will provide a better topic, although recent advances in biotelemetry have understanding of how critical these habitats are to this made such research feasible (Voegeli et al. 2001; species. There is also increasing evidence that loss of Heupel et al. 2006). apex predators from coastal environments may induce Lemon sharks (Negaprion bevirostris)arean a number of cascades that could dramatically alter excellent example of a species that uses nearshore ecosystem structure and function (Jackson et al. 2001; lagoons, bays, tidal creeks, and other coastal areas for Myers et al. 2007). Hence, sharks and shark habitat juvenile habitat (see Wetherbee et al. 2007). This require protection from exploitation and habitat shark is common on Atlantic coasts from USA to destruction. Furthermore, the World Conservation Brazil, and possibly in some West African countries, Union/Species Survival Commission (IUCN/SSC) and in the Pacific from Baja, California to Ecuador rates lemon sharks as “Near Threatened”. As such, (Compagno 1984). Maturing between 11 to 13 years telemetric information on the spatial ecology of of age, or approximately 235 cm in total length juvenile lemon sharks beyond the waters of Bimini (Brown and Gruber 1988; Castro 1993), successfully (i.e., Sundström et al. 2001) will provide critical fertilized females will deliver 4–18 offspring in information needed to make informed decisions Environ Biol Fish regarding the conservation status and protection of were positioned vertically in the water column. In lemon sharks (Cooke 2008). water <1 m deep at low tide and at narrow choke Given the information above, the objective of this points, receivers were deployed horizontally or 5–10 study was to document the habitat use and movement degrees above horizontal, with the hydrophone patterns of juvenile lemon sharks in nursery areas oriented to maximize coverage and ensure continual near Cape Eleuthera, Eleuthera, The Bahamas. Unlike submersion. Range tests determined that receivers the earlier work of Gruber and colleagues that focused located in water greater than 1 m had a radius primarily on a single, predominantly closed lagoon coverage of 250 m, whereas receivers in shallow system and the use of manual tracking (but see water (<1 m) had a radius coverage of as little as Wetherbee et al. 2007), this study examines the 30 m, due to shoreline confinement. Although the movement of juvenile lemon sharks along a section range of coverage for receivers in shallow water or of open coastline with a number of discrete tidal positioned horizontally was considerably less, they mangrove creek systems using a passive acoustic did provide the necessary coverage to monitor choke telemetry array. This work will enable us to evaluate points (e.g., creek mouths), such that data correction the extent to which tagged individual juvenile lemon for receiver range was not required. Wind and wave sharks exhibit site fidelity in a relatively open conditions as well as water depth and tidal cycles environment, where the possibility of long-distance influenced the detection range of individual receivers movement exists. Furthermore, we will evaluate the (Heupel et al. 2006). Even at slack low tides, all of the diurnal and seasonal movement patterns of juvenile receivers were covered by at least 20 cm of water and lemon sharks to reveal any temporal trends in their had the potential to receive signals from tagged use of habitat. juvenile sharks. Receivers were deployed between November 2005 and May 2007 (5 in November 2005, 6 in February 2006, 15 in October 2006, and 1 in May Materials and methods 2007) as resources were available, and were visited regularly for downloading and cleaning. Study site and hydrophone array set-up Shark capture, tagging and passive monitoring This study was conducted along a 23 km stretch of the north coast of Cape Eleuthera, Eleuthera, The Juvenile lemon sharks were angled from Page, Bahamas (N 24 50 05 and W 76 20 32) (Fig.