Abstract
AbstractThe Pacific sleeper shark Somniosus pacificus is one of the largest predators in deep Suruga Bay, Japan. A single individual of the sleeper shark (female, ~300 cm in total length) was observed with two baited camera systems deployed simultaneously on the deep seafloor in the bay. The first arrival was recorded 43 min after the deployment of camera #1 on 21 July 2016 at a depth of 609 m. The shark had several remarkable features, including the snout tangled in a broken fishing line, two torn anteriormost left-gill septums, and a parasitic copepod attached to each eye. The same individual appeared at camera #2, which was deployed at a depth of 603 m, ~37 min after it disappeared from camera #1 view. Finally, the same shark returned to camera #1 ~31 min after leaving camera #2. The distance between the two cameras was 436 m, and the average groundspeed and waterspeed of the shark were 0.21 and 0.25 m s−1, respectively, which were comparable with those of the Greenland shark Somniosus microcephalus (0.22–0.34 m s−1) exhibiting the slowest comparative swimming speed among fish species adjusted for size. The ambient water temperature of the Pacific sleeper shark was 5.3 °C, which is considerably higher than that of the Greenland shark (~2 °C). Such a low swimming speed might be explained by the ‘visual interactions hypothesis’, but it is not a consequence of the negative effects of cold water on their locomotor organs.
Highlights
The genus Somniosus is a widely distributed group of deep-water sleeper sharks belonging to the family Somniosidae, and five species have been recognized to date: S. antarcticus Whitley, 1939, S. longus (Tanaka, 1912), S. microcephalus (Bloch & Schneider, 1801), S. pacificus Bigelow & Schroeder, 1944, and S. rostratus (Risso, 1827)
The sharks cruised at 0.34 m s−1 with a tail-beat frequency of 0.15 Hz, both of which were the lowest values across all fish species, adjusted for their size; reportedly, the swimming performance of Greenland sharks was limited by cold waters (∼2 °C) (Watanabe et al, 2012)
The sharks cruised at 0.34 m s−1 with a tail-beat frequency of 0.15 Hz, both of which were the lowest values across fish species, adjusted for their size (Watanabe et al, 2012)
Summary
The genus Somniosus is a widely distributed group of deep-water sleeper sharks belonging to the family Somniosidae, and five species have been recognized to date: S. antarcticus Whitley, 1939, S. longus (Tanaka, 1912), S. microcephalus (Bloch & Schneider, 1801), S. pacificus Bigelow & Schroeder, 1944, and S. rostratus (Risso, 1827). The most well-studied species within the genus is the Greenland shark S. microcephalus, which is distributed in the North Atlantic and adjacent Arctic with a wide vertical distribution range from the surface to the deep sea and a maximum habitat depth of 2992 m (Watanabe et al, 2012; Mecklenburg et al, 2018). The swimming speed of Greenland sharks was estimated from video analyses, which showed the average swimming speed of 0.27 m s−1 (SD = 0.07; range 0.15–0.42 m s−1) and no significant correlation between shark length and swimming speed (Devine et al, 2018). Archival pop-off tag tracking of Greenland sharks in the high Arctic waters showed that the average distance travelled is 0.6–16.6 km day−1 (Fisk et al, 2012)
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