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Postrelease Survival, Vertical and Horizontal Movements, and Thermal Habitats of Five Species of Pelagic Sharks in the Central

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Postrelease Survival, Vertical and Horizontal Movements, and Thermal Habitats of Five Species of Pelagic Sharks in the Central 341 Abstract—From 2001 to 2006, 71 Postrelease survival, vertical and horizontal pop-up satellite archival tags (PSATs) were deployed on five species of movements, and thermal habitats of five species pelagic shark (blue shark [Prionace glauca]; shortfin mako [Isurus oxy- of pelagic sharks in the central Pacific Ocean rinchus]; silky shark [Carcharhinus falciformis]; oceanic whitetip shark Michael K. Musyl (contact author)1 [C. longimanus]; and bigeye thresher 2 [Alopias superciliosus]) in the central Richard W. Brill Pacific Ocean to determine species- Daniel S. Curran3 specific movement patterns and sur- 4 vival rates after release from longline Nuno M. Fragoso fishing gear. Only a single postrelease Lianne M. McNaughton1 mortality could be unequivocally doc- Anders Nielsen5 umented: a male blue shark which 3* succumbed seven days after release. Bert S. Kikkawa Meta-analysis of published reports Christopher D. Moyes6 and the current study (n=78 reporting Email address for contact author: [email protected] PSATs) indicated that the summary effect of postrelease mortality for blue * Deceased 3 Pacific Islands Fisheries Science Center sharks was 15% (95% CI, 8.5–25.1%) NOAA Fisheries 1 University of Hawaii and suggested that catch-and-release 2570 Dole Street Joint Institute for Marine and Atmospheric in longline fisheries can be a viable Honolulu, Hawaii 96822 Research (JIMAR) management tool to protect paren- Kewalo Research Facility/NOAA 4 Large Pelagics Research Center tal biomass in shark populations. 1125B Ala Moana Boulevard 108 East Main Street Pelagic sharks displayed species-spe- Honolulu, Hawaii 96814 Gloucester, Massachusetts 01930 cific depth and temperature ranges, 5 although with significant individual 2 Northeast Fisheries Science Center Technical University of Denmark temporal and spatial variability in National Marine Fisheries Service National Institute of Aquatic Resources vertical movement patterns, which Woods Hole, Massachusetts and Jægersborg Allé 1 were also punctuated by stochastic Virginia Institute of Marine Science 2920 Charlottenlund, Denmark events (e.g., El Niño-Southern Oscil- P.O. Box 1346 6 Department of Biology lation). Pelagic species can be sepa- Gloucester Point, Virginia 23062 Queen’s University rated into three broad groups based Kingston, ON, K7L 3N6, Canada on daytime temperature preferences by using the unweighted pair-group method with arithmetic averaging clustering on a Kolmogorov-Smirnov D distance matrix: 1) epipelagic max Although there is considerable dis- predators. Moreover, commercial and species (silky and oceanic whitetip sharks), which spent >95% of their agreement and uncertainty about the recreational fishing activities gener- time at temperatures within 2°C of current state of pelagic fish popula- ally remove the largest animals (i.e., sea surface temperature; 2) meso- tions (Burgess et al., 2005; Hampton parental biomass) and heavy selec- pelagic-I species (blue sharks and et al., 2005; Sibert et al., 2006), there tion pressure over several decades can shortfin makos, which spent 95% of is general agreement that large apex potentially cause evolutionary effects their time at temperatures from 9.7° predators, particularly sharks, are (e.g., heritable changes in life-history to 26.9°C and from 9.4° to 25.0°C, at greatest risk of overfishing (Baum traits such as body size, growth, respectively; and 3) mesopelagic-II et al., 2003; Baum and Myers, 2004; age-at-maturity, and fecundity; Law, species (bigeye threshers), which Camhi, 2008). Possessing life-history 2000; DiBattista et al., 2009; Genner spent 95% of their time at tempera- characteristics (e.g., slow growth, long et al., 2009). tures from 6.7° to 21.2°C. Distinct thermal niche partitioning based on gestation, late maturity) that evolved Large pelagic sharks, particularly body size and latitude was also evi- in the absence of industrial fishing, blue sharks, which form a large part dent within epipelagic species. pelagic shark species are susceptible of the international shark fin trade to overfishing, and declining trends in (Clarke et al., 2006), are generally some populations need to be reversed not targeted but are by far the ma- for parental biomass to rebuild stocks jority of the bycatch in pelagic gill (Camhi, 2008; Chang and Liu, 2009; nets and longline fisheries targeting Manuscript submitted 11 January 2011. Manuscript accepted 16 May 2011. Dulvey et al., 2008). With food web swordfish (Xiphias gladius) (Camhi, Fish. Bull. 109(4):341–368 (2011). models, Schindler et al. (2002) pre- 2008; Mandelman et al., 2008; Na- dicted that continued mortality of blue kano and Stevens, 2008). Effective The views and opinions expressed shark (Prionace glauca) in longline strategies to mitigate shark bycatch or implied in this article are those of the author (or authors) and do not necessarily fisheries in the central Pacific could requires knowledge of species-specif- reflect the position of the National Marine adversely affect their populations ic horizontal and, more importantly, Fisheries Service, NOAA. and the role of this species as apex vertical movement patterns (e.g., Wat- 342 Fishery Bulletin 109(4) son et al., 2009). Knowledge of these vertical move- ogy and ecology of these apex predators (Bonfil, 2008; ment patterns may allow fishing crews to target the Bonfil, et al., 2008; Dulvy et al., 2008). Results from opportunity of mismatch between hook depth and the this study extend the work presented in Moyes et al. sharks’ vertical distributions and thus possibly mini- (2006) and are expected to be useful in the mitigation mize bycatch (Beverly et al., 2009). For effective man- of shark bycatch and mortality. agement measures to be implemented, it is also benefi- cial to have accurate estimates of both at-vessel and postrelease mortality rates (Carruthers et al., 2009). Materials and methods These data are necessary for estimating total fishery- induced mortality and for improving stock assessments Sharks were caught by pelagic longline fishing gear (Kitchell et al., 2004). Mitigation strategies could then (from March 2001 through November 2006) deployed be given special consideration for species with high from the NOAA research vessels Townsend Cromwell rates of postrelease mortality (Carruthers et al., 2009). and Oscar Elton Sette and by using methods described Information on postrelease mortality in blue sharks in Moyes et al. (2006). In brief, longline gear (~400–800 (Carey and Scharold, 1990; Weng et al., 2005; Moyes hooks per set) was deployed at night (usually immedi- et al., 2006; Campana et al., 2009a; Queiroz et al., ately after dusk) and retrieved in the morning. Because 2010; Stevens et al., 2010), bigeye threshers (Alopias we used four to six hooks between floats; hook depths superciliosus) (Nakano et al., 2003; Weng and Block, were generally <100 m as determined by attached time- 2004), shortfin makos (Isurus oxyrinchus) (Holts and temperature-depth recorders (Wildlife Computers, Red- Bedford, 1993; Klimley et al., 2002; Sepulveda et al., mond, WA). 2004; Loefer et al., 2005), and common thresher sharks Soak times ranged from 10 to 24 hours with an aver- (A. vulpinus) (Heberer et al., 2010) is available from age of 15 hours, and before 2004, we employed 15/0 size studies with acoustic tracking and pop-up satellite ar- circle hooks, squid (Illex spp.) bait, and green chemical chival tags (PSATs). In two studies (Moyes et al., 2006; light sticks attached to the monofilament nylon leader Campana et al., 2009a), the investigation of postrelease ~90 cm above each hook. However, because of regula- mortality of blue sharks released from longline fishing tions introduced in 2004 to reduce sea turtle bycatch gear was the primary goal, but mortality rates may in the Hawaii-based shallow-set (nighttime) commer- have been confounded by specific aspects of fishing cial longline fishery targeting swordfish (Gilman et al., practices (Musyl et al., 2009). Hook type, time spent 2007; Walsh et al., 2009), we began using 16/0 and 18/0 hooked on the line, fight time, leader material, fish circle hooks (no offset), and Pacific saury (sanma, Colo- size, and handling and discard practices can influence labis saira) as bait. In addition, to improve shark catch the at-vessel and postrelease mortality of pelagic shark rates by reducing bite-offs from monofilament leaders, species (e.g., Diaz and Serafy, 2005; Moyes et al., 2006; we added ~25 cm of seven-strand braided stainless steel Campana et al. 2009a; Carruthers et al., 2009; Heberer cable immediately above the hook. et al. 2010; Hoey and Moore1). Sharks were hoisted aboard by a sling and restrained Our goals were to measure postrelease mortality by the crew as described in Moyes et al. (2006). Sharks rates and vertical movement patterns in the five most showing an absence of movements or reaction of the commonly captured pelagic shark species in the Hawaii- nictitating membrane to light touching of the eye were based commercial longline fishery: blue sharks, big- deemed dead and were not tagged (i.e., these samples eye threshers, oceanic whitetip sharks (Carcharhinus would bias the postrelease mortality estimate). Tagged longimanus), shortfin makos, and silky sharks (C. fal- sharks were measured to the nearest centimeter for ciformis)(Walsh et al., 2009). All five species represent total length (TL), and hooks were removed by cutting a significant portion of the shark bycatch in global fish- them in half with bolt cutters unless they were too eries and their life history characteristics make popu- deeply ingested, in which case, the leader line was cut lations vulnerable to fishing pressure (Cortés, 2000; as close to the mouth of a shark as possible. PSATs Camhi, 2008; Dulvy et al., 2008; Stevens, 2008; Chang (model PTT-100, Microwave Telemetry, Columbia, MD) and Liu, 2009). Moreover, there is little or no informa- were affixed to the dorsal fin by drilling a 10–15 mm -di tion about their postrelease survival, population ecology, ameter hole near the base of the fin and threading sev- and movement patterns in the central Pacific Ocean.
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