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Range Extension of the Endangered Great Hammerhead Shark Sphyrna Mokarran in the Northwest Atlantic: Preliminary Data and Significance for Conservation

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Range Extension of the Endangered Great Hammerhead Shark Sphyrna Mokarran in the Northwest Atlantic: Preliminary Data and Significance for Conservation Vol. 13: 111–116, 2011 ENDANGERED SPECIES RESEARCH Published online January 27 doi: 10.3354/esr00332 Endang Species Res NOTE Range extension of the Endangered great hammerhead shark Sphyrna mokarran in the Northwest Atlantic: preliminary data and significance for conservation Neil Hammerschlag1, 2, 3,*, Austin J. Gallagher2, 3, Dominique M. Lazarre1, 3, Curt Slonim3, 4 1Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149, USA 2Leonard and Jayne Abess Center for Ecosystem Science and Policy, University of Miami, PO Box 248203, Coral Gables, Florida 33124, USA 3RJ Dunlap Marine Conservation Program, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149, USA 4Curt-A-Sea Fishing Charters, 117 El Capitan Drive, Islamorada, Florida 33036, USA ABSTRACT: We provide pilot data from a satellite-tracked great hammerhead shark Sphyrna mokar- ran in the Atlantic, representing the first such data on this species in the literature. The 250 cm shark was tagged off the coast of the middle-Florida Keys (USA) and transmitted for 62 d. During this time it migrated a minimum distance of ~1200 km northeast from the coast of Florida, into pelagic interna- tional waters of the Northwest Atlantic. When compared to the primary literature, this migration rep- resented a northeasterly range extension for this species off the continental slope in the Atlantic. The significance of this range extension is discussed in terms of the vulnerability of S. mokarran to target and non-target fisheries. KEY WORDS: Predator · Satellite tag · Argos · Shark · Habitat use · Elasmobranch Resale or republication not permitted without written consent of the publisher INTRODUCTION directly targeted in the Northwest Atlantic, S. mokar- ran is taken as bycatch in several fisheries and suffers The great hammerhead shark Sphyrna mokarran one of the highest discard mortality rates of any shark is the largest of the hammerhead species (family species in the Atlantic (National Marine Fisheries Ser- Sphyrnidae) and is widely distributed in coastal and vice 2002). In the Northwest Atlantic, S. mokarran pelagic tropical waters (Compagno et al. 2005). S. have been reported to experience greater than 90% at- mokarran is distinguishable from its smaller congeners vessel mortality rates in the US bottom longline fishery by a large sickle-shaped dorsal fin and broad cephalo- (Commercial Shark Fishery Observer Program as foil lacking a notch. Clarke et al. (2006) recently reported by Denham et al. 2010). A recent study esti- demonstrated that the shark fin trade is a major driver mated age and growth of S. mokarran based on verte- of global shark declines. Great hammerheads are brae removed from 216 sharks that were retained by highly sought after in the finning industry due to their research-fishing (Piercy et al. 2010). The study demon- large fins, and the high fin needle content (cartilagi- strated that great hammerheads have one of the oldest nous fibers) common to all hammerheads (Abercrom- reported ages (44 yr) for any elasmobranchs (Piercy et. bie et al. 2005, Chapman et al. 2009). Although not al. 2010). Additionally, S. mokarran only reproduces *Email: [email protected] © Inter-Research 2011 · www.int-res.com 112 Endang Species Res 13: 111–116, 2011 once every 2 yr, making this species vulnerable to rap- MATERIALS AND METHODS id over-exploitation and population declines (Stevens & Lyle 1989, Denham et al. 2010). To provide insights into the spatial habitat use of Recent studies have demonstrated that, globally, great hammerheads in the subtropical Atlantic Ocean, populations of great hammerheads have drastically we conducted a pilot study off the Florida Keys, USA. declined (Baum et al. 2003, Shepherd & Myers 2005, A male shark (250 cm total length) was tagged on Myers et al. 2007, Ferretti et al. 2008). In the Atlantic 20 February 2010, with a near-real time Smart Position alone, hammerhead stocks, including Sphyrna mokar- and Temperature Transmitting (SPOT5) satellite tag ran, have been estimated to have declined over 89% (Fig. 1). The shark was captured in US federal waters between 1986 and 2000 (Myers et al. 2007). This loss of off the reef edge in the middle Florida Keys (~24.69° N, apex predatory sharks in the Atlantic has been sug- 80.85° W; Fig. 2) using baited drumlines as described gested to induce major cascading ecosystem level by Hueter & Tyminski (2007). Drumlines were left to effects (e.g. Myers et al. 2007). Accordingly, the Inter- soak for 1 h before being checked for shark presence, national Union for the Conservation of Nature (IUCN) to reduce the stress of capture, before applying the Red List of Threatened Species lists S. mokarran as satellite tag. To limit bio-fouling of the tag, the trans- ‘Endangered’ with population trends decreasing glob- mitter was coated with Propspeed, a non-toxic, non- ally (www.iucnredlist.org). In November 2010, the metallic, anti-fouling agent comprised of several dif- International Commission for the Conservation of ferent types of silicone resins that inhibit attachment of Atlantic Tunas (ICCAT) adopted agreements to protect marine growth (Hammerschlag et al. 2010). The coated great hammerheads in Atlantic waters (www.iccat.int). SPOT tag was attached to the first dorsal fin of the In order to implement appropriate conservation man- shark (following Weng et al. 2005) using titanium bolts, agement strategies, the ICCAT Standing Committee neoprene washers, steel washers, and high carbon on Research and Statistics (SCRS) recommended steel nuts following Hanson (2001). The attachment immediate implementation of ‘research on hammer- metals were selected to ensure that the steel nuts head sharks in the Convention area (Atlantic) […] Based would corrode, resulting not only in tag detachment on this research, CPCs [contracting parties and coop- (Hanson 2001), but also to prevent any metallic corro- erating non-contracting parties, entities or fishing enti- sion from touching the shark fin (Hammerschlag et al. ties] shall consider time and area closures and other 2010). SPOT tags contain a saltwater switch, which measures, as appropriate.’ (www.iccat.int/documents/ activates the tag to transmit to an orbiting satellite recs/RECS_ADOPTED_2010_ENG.pdf) As such, there when above the water surface. Geographic locations of is a management and conservation push to identify the shark were determined by Doppler-shift calcula- and characterize areas important to the life history of tions made by the Argos Data Collection and Location hammerhead sharks in the Atlantic. Service whenever a passing satellite received 2 or The great hammerhead’s geographic range is known to extend throughout coastal warm temperate and tropical waters, occurring within latitudes 40° N to 35° S (Last & Stevens 1994). In the western Atlantic Ocean, they have been positively documented within coastal waters as far south as Uruguay and as far north as North Carolina (Compagno et al. 2005, Denham et al. 2010). While there have been a few individual reports of great hammer- heads north of the aforementioned range, these claims are either unsub- stantiated or not valid (see ‘Discussion’ for further details). This paper docu- ments a northeasterly range extension of Sphyrna mokarran, off the continen- tal slope in the Northwest Atlantic, and describes the possible significance of Fig. 1. Sphyrna mokarran. Tagged great hammerhead shark swimming off with these preliminary data for the conser- a SPOT5 satellite tag attached to its large sickle-shaped dorsal fin, which is vation of this species. characteristic of this species. Image courtesy of K. Slonim Hammerschlag et al.: Range extension in Sphyrna mokarran 113 Fig. 2. Sphyrna mokarran. (A) Southeastern USA, showing the known distribution of great hammerheads (red) based on Com- pagno et al. (2005). (B) Locations of a great hammerhead shark tracked with a SPOT5 satellite tag between 20 February and 22 April 2010. Tracks were filtered to provide 7 locations (stars) with accuracies ranging from approximately 500 m to 5 km. Loca- tions in the Atlantic (~500 km west of New Jersey) acquired from 20 to 22 April. Locations acquired in the Florida Keys region be- tween 20 February and 18 March. The straight-line distance from the locations recorded in the middle of the Northwest Atlantic to the initial tagging location in the Keys was ~1200 km. See ‘Results and Discussion’ for further details more signals from the tag at the surface. With each RESULTS AND DISCUSSION position, Argos provides an associated accuracy esti- mate for the following location classes (LC): LC 3, The shark was tracked from 20 February to 22 April <250 m; LC 2, <500 m; and LC 1, <1500 m (www. 2010, providing data on date and time of surfacing as argos-system.org). Argos does not provide estimates well as ambient water temperature at transmission. for LC 0, A, B, and Z; however, it has been reported in The shark provided 45 total position estimates during the literature that LC A is accurate to approximately this period, but tracks were filtered to remove positions 1 km radius and LC B is accurate to approximately with accuracy estimates below LC B. This provided a 5 km radius (Tougaard et al. 2008). Class Z indicates data set of 7 spatial locations (Fig. 2) with accuracies that the location process failed and estimates of posi- ranging from approximately 500 m to 5 km. This error tion are highly inaccurate. scale, when compared to the scale of shark movement,
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