Sexual segregation of pelagic sharks and the potential threat from fisheries. Biol Lett 5:156-159

Instituto de Investigaciones Marinas, CSIC, Eduardo Cabello 6, 36208 Vigo, Spain.
Biology letters (Impact Factor: 3.25). 05/2009; 5(2):156-9. DOI: 10.1098/rsbl.2008.0761
Source: PubMed


Large pelagic sharks are declining in abundance in many oceans owing to fisheries exploitation. What is not known however is whether within-species geographical segregation of the sexes exacerbates this as a consequence of differential exploitation by spatially focused fisheries. Here we show striking sexual segregation in the fastest swimming shark, the shortfin mako Isurus oxyrinchus, across the South Pacific Ocean. The novel finding of a sexual 'line in the sea' spans a historical longline-fishing intensity gradient, suggesting that differential exploitation of the sexes is possible, a phenomenon which may underlie changes in the shark populations observed elsewhere.

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Available from: Gonzalo Mucientes, Oct 08, 2015
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    • "Many species of elasmobranch are highly mobile (Templeman 1976, Gauld 1982, Grubbs et al. 2007, Gore et al. 2008, Mucientes et al. 2009) and display complex temporal and spatial movement patterns (Hyrenbach et al. 2000). However, site association is being increasingly recognised for many elasmobranchs , often associated with critical habitats and important life history stages. "
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    ABSTRACT: Identification and incorporation of residential behaviour into elasmobranch management plans has the potential to substantially increase their effectiveness by identifying sites where marine protected areas might be used to help conserve species with high migratory potential. There is evidence that the spurdog Squalus acanthias displays site association in some parts of its global distribution, but this has currently not been shown within the North East Atlantic where it is Critically Endangered. Here we investigated the movements of electronically tagged spurdog within Loch Etive, a sea loch on the west coast of Scotland. Archival data storage tags (DSTs) that recorded depth and temperature revealed that 2 mature female spurdog overwintered within the loch, restricting their movements to the upper basin, and remaining either in the loch or the local vicinity for the rest of the year. This finding was supported by evidence for limited movements from conventional mark−recapture data and from an acoustically tagged individual spurdog. Some of the movements between the loch basins appear to be associated with breeding and parturition events. This high level of site association suggests that spatial protection of the loch would aid the conservation of different age and sex classes of spurdog.
    Marine Ecology Progress Series 04/2015; 526:113-124. DOI:10.3354/meps11210 · 2.62 Impact Factor
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    • "For example, several studies have reported that large elasmobranch species tend to have a low reproductive and Sims, 2008; Noriega et al., 2011). Additionally, the formation of permanent or seasonal aggregations can increase an elasmobranch population's vulnerability to overexploitation (Wearmouth and Sims, 2008; Mucientes et al., 2009; Jacoby et al., 2011), especially when there is a high overlap between aggregation sites and fishing grounds (Jacoby et al., 2011). Elasmobranchs are a common component of the bycatch in tropical bottom trawling fisheries (Stobutzki et al., 2002; Walker, 2005). "
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    ABSTRACT: The elasmobranch bycatch associated with the Costa Rican deepwater shrimp fishery is mainly comprised of four species: Raja velezi, Mustelus henlei, Zapteryx xyster and Torpedo peruana. In data-deficient fisheries such as this one, knowledge of the reproductive ecology of a species may serve as a valuable management tool to determine its vulnerability and apply precautionary measures to ensure its long-term conservation. This study examined the reproductive ecology of R. velezi, M. henlei, Z. xyster and T. peruana based on data collected during demersal trawling along the Pacific coast of Costa Rica, Central America. A total of 290 trawls was analyzed at depths of 18–350 m (March 2010–August 2012). While R. velezi, M. henlei and Z. xyster matured at similar sizes (range: 37–60 cm TL), T. peruana matured at a larger size (70 cm TL in females). The four elasmobranch species exhibited strong sex and size segregation patterns, which were mainly influenced by depth. Adults were more common at depths >50 m, whereas neonates and gravid females were more abundant in shallow estuarine waters (<50 m). Moreover, large aggregations of immature R. velezi and M. henlei occurred near coastal wetlands, bays and estuaries of the central Pacific region. These results suggest that shallow estuarine habitats may be important for early life stages of demersal elasmobranchs caught in the Costa Rican trawling fishery. However, our knowledge of critical habitats for elasmobranch along the entire Pacific of Costa Rica is still limited, and thus future studies are needed to identify and understand the role of these habitats in the early life-history of sharks, skates and rays.
    Fisheries Research 09/2014; 157:96–105. DOI:10.1016/j.fishres.2014.04.003 · 1.90 Impact Factor
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    • "The potential role of sexual segregation in exploiting com - mercial shark species has rarely been acknowledged . In a study analyzing the commercial longline catch composition of Short - fin Mako Sharks Isurus oxyrinchus in the South Pacific Ocean ( Mucientes et al . 2009"
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    ABSTRACT: The international exploitation of the gonochoristic and sexually segregated spiny dogfish (Squalus acanthias) is driven by the European market, which favors large females. This sex-selective demand is likely affecting the fishery sustainability of the U.S. Atlantic stock, which is measured using the spawning stock biomass of adult females as a main reference point. A potential management strategy to enhance the fishery sustainability would be the development of a male-only directed fishery in areas characterized by a consistent and predictable presence of males, although this information is currently lacking. We conducted fishery-dependent surveys for spiny dogfish in the Cape Cod, Massachusetts area to assess if the percentage of males in the catch changes throughout a normal fishing day, an event frequently observed by local commercial longliners. A consistent seasonal (summer and early fall) diurnal shift in the sex ratio was found within 10 miles off the east coast of Cape Cod. This shift suggests the potential for a pilot study testing the viability of a male-only directed longline fishery in this area based on season and time of the day. Such a fishery would enhance the sustainability of the U.S. Atlantic spiny dogfish stock by reducing fishing pressure on adult females
    American Fisheries Society 144th Annual Meeting; 08/2014
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