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Chapter 9 - Large Pelagic Fisheastern Atlantic births may occur more frequently in thefall and winter (Compagno 2001). Gestation period isthought to be about 12 months long, and females givebirth to two fully developed pups per litter that are 100to 140 cm long (Gruber and Compagno 1981; Compagno2001). Juveniles of this species are both coastal and oceanicand most are found along the eastern Atlantic coastand Gulf of Mexico just outside 200m depth contour(Kohler et al. 1998). Adults are marine and can rangefrom inshore shallow depths of 1 m to the high seas atdepths of 500 m, but mostly below 100 m (Compagno2001). Maximum published total length for females is 422cm; males 357 cm (Compagno 2001); and weight is 363.8kg. These animals feed on squid and pelagic fishes (e.g.herring and mackerel), small billfishes and bottom fishes(e.g. hake) (Compagno 2001; NMFS 2009). Many scientistsbelieve that they stun or kill their prey with theirlarge, elongated tail fin; bigeye thresher caught by theirtails on longlines and sport fishing supports this theory(Compagno 2001).Thresher Shark (Alopius vulpinus)Thresher sharks are circumglobal in tropical to cold-temperateseas (Compagno 2001). They are found in coastalwaters over continental shelves and around islands, wherethey are abundant inshore, but have been found up to366 m (Strasburg 1958; Compagno 2001). These sharksthroughout the Northwest Atlantic, mostly along or withinthe 200 m depth contour (Kohler et al. 1998; NMFS2009). The thresher shark has a thermoconservationmechanism, meaning that they are able to maintain a bodytemperature above ambient water temperature (Sepulvedaet al. 2005).At this time, there is limited information on threshershark breeding grounds within Northwest Atlantic. Thesize at which they reach sexual maturity at about 330 cmin males and 260-450 cm in females, which may vary byregion (Collette and Klein-MacPhee 2002). These sharksare ovoviviparous and female sharks have an average littersize of 2-4 pups per litter (Collette and Klein-MacPhee2002). Juveniles are marine and often found inshore andin warm shallow bays (Compagno 2001). These animalsshow spatial and depth segregation by sex (IUCN 2007a).Adult thresher sharks are apex predators at the highesttrophic level of Atlantic sharks (Estrada et al. 2003).These sharks may cooperate with each other to hunt and,like the bigeye thresher, stun their prey using their largetail fin. Thresher sharks may grow to a total length of600 cm (Collette and Klein-MacPhee 2002). This speciesfeeds on schooling fishes, including squid, herring,mackerels, bluefishes, clupeids, and occasionally seabirds(Compagno 2001).Porbeagle (Lamna nasus)The porbeagle shark is commonly found in deep, coldtemperate waters of the North Atlantic, South Atlantic,and South Pacific Oceans (Castro 1983). This species iscommon in pelagic waters (from coastal waters up to 300m), and is most abundant on the continental shelf, buthas occasionally been found far from land (Castro 1983;Compagno 2001; Collette and Klein-MacPhee 2002).Porbeagles are thermoconserving and can maintain bodytemperatures that are 7-10 o C warmer than ambient watertemperatures (Carey and Teal 1969). The porbeagle generallyprefers waters colder than 18 o C (Collette and Klein-MacPhee 2002). Porbeagle may occur singly as well as inschools and feeding aggregations (IUCN 2007a). Taggingdata suggest maximum travel of 1000km (Campana et al.2003). Porbeagle populations of the Northwest Atlanticare mostly separate from those of the northeast, andpopulations in the northern hemisphere are most likelyseparate from those in the southern hemisphere (Franciset al. 2008). They tend to come inshore and to the surfaceduring summer months, but stay at depth in offshore watersduring winter (Collette and Klein-MacPhee 2002).In the Northwest Atlantic, porbeagle sharks breed betweenNew Jersey to Newfoundland from fall to winterand pregnant individuals are caught from Massachusettsto Maine year-round (Campana et al. 2003). Gestationlasts between 8 and 9 months (Francis et al. 2008). Thesesharks are ovoviviparous and oophagus during late stageof development (Collette and Klein-MacPhee 2002).The pelagic, obligate marine juveniles are born in springto summer and there are approximately 4 pups per litter9-32Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report