Feeding habits of the blue shark, Prionace glauca, and salmon shark, Lamna ditropis, in the transition region of the Western North Pacific

Abstract

We describe the feeding habits of 70 blue sharks (Prionace glauca) and 39 salmon sharks (Lamna ditropis) caught at 0-7 m depth at night by research drift gillnets in the transition region of the western North Pacific during AprilMay of 1999 and 2000. Blue sharks of 50-175 cm total length fed on a large variety of prey species, consisting of 24 species of cephalopods and 16 species of fishes. Salmon sharks of 69-157 cm total length fed on a few prey species, consisting of 10 species of cephalopods and one species of fish. Important prey for the blue sharks were large, non-active, gelatinous, meso-to bathypelagic cephalopods (e.g., Chiroteuthis calyx, Haliphron atlanticus, Histioteuthis dofleini and Belonella borealis) and small myctophid fishes. Important prey for the salmon sharks were midsized, active, muscular, epi-to mesopelagic squids (e.g. Gonatopsis borealis, Onychoteuthis borealijaponica and Berryteuthis anonychus). Our results suggest that blue sharks feed on cephalopods mainly during the daytime when they descend to deep water. Salmon sharks may feed opportunistically with no apparent diurnal feeding period. Blue sharks and salmon sharks have sympatric distribution in the transition region in spring; they have different feeding habits and strategies that reduce competition for food resources.

Vertical distribution, behavior, chemical composition and metabolism of Stauroteuthis syrtensis (Octopoda: Cirrata) in the northwest Atlantic

“…In response to disturbance caused by the submersibles, Stauroteuthis syrtensis inflated its web complex and exhibited the ballooning behavior noted previously (Vecchione & Young 1997, Johnsen et al 1999. Thus, observations in the present study supported the hypothesis that these behaviors may function as an alarm response to deter or confuse predators, such as Cuvier's beaked whales Ziphius cavirostris and blue sharks Prionace glauca (Vecchione & Young 1997, Johnsen et al 1999, Santos et al 2001, Kubodera et al 2007. Observations also indicated that slow sculling of the paired fins, medusoid contractions of the web, and rapid fin sculling were similar to patterns of locomotion reported for another deep-water cephalopod, Vampyroteuthis infernalis (Seibel et al 1998).…”

Feeding chronology of six species of carcharhinid sharks in the western North Atlantic Ocean as inferred from longline capture data

“…Additionally, studies utilizing stomach contents to examine the feeding chronology of large-bodied species almost exclusively focus on neonates and juveniles (e.g. Medved et al 1985, Cortés & Gruber 1990, Bush 2003, Barry et al 2008, Kubodera et al 2007, TorresRojas et al 2010, with the notable exception of Barnett et al (2010) who examined stomachs from all size classes of broadnose sevengill sharks Noto rhynchus cepedianus. Conversely, our method includes all life stages that are susceptible to longline gear.…”

“…For example, Sciarrotta & Nelson (1977) tracked 14 blue sharks Prionace glauca in the eastern Pacific Ocean and found these sharks to be most active during nocturnal periods, as indicated by increased frequency of dives through the water column. This finding led the authors to conclude that while blue sharks feed during all hours of the day, peak feeding occurs at night; however, based on analyses of stomach contents, Kubodera et al (2007) concluded that blue sharks in the western Pacific Ocean feed primarily during the day.…”

“…For example, Sciarrotta & Nelson (1977) tracked 14 blue sharks Prionace glauca in the eastern Pacific Ocean and found these sharks to be most active during nocturnal periods, as indicated by increased frequency of dives through the water column. This finding led the authors to conclude that while blue sharks feed during all hours of the day, peak feeding occurs at night; however, based on analyses of stomach contents, Kubodera et al (2007) concluded that blue sharks in the western Pacific Ocean feed primarily during the day.While analyses of stomach content and telemetry data have provided valuable information on the feeding chronology of sharks, an overlooked method of examining diel feeding activity is the use of baited hooks which, with the exception of foul hooking, require that a shark voluntarily approach and actively attempt to feed in order to be captured. To our knowledge, only 2 studies have investigated diel trends in catch rates, albeit briefly, of a shark species using baited gear (Medved & Marshall 1981, Heithaus 2001.…”

Stable isotope analysis of vertebrae reveals ontogenetic changes in habitat in an endothermic pelagic shark

“…This suggests that stable isotope composition of juvenile sharks reflects use of the NPTZ nursery. The NPTZ is a dynamic and productive oceanic region bounded by the subarctic and subtropical frontal zones that has been shown to be an important foraging area and migratory corridor for a variety of pelagic predators [42], including juvenile salmon sharks [12,35]. rspb.royalsocietypublishing.org Proc.…”