First Record Of Swimming Speed Of The Pacific Sleeper Shark Somniosus Pacificus Using A Baited Camera Array

The Pacific sleeper shark Somniosus pacificus is one of the largest predators in deep Suruga Bay, Japan. A single individual of the sleeper shark (female, similar to 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, similar to 37 min after it disappeared from camera #1 view. Finally, the same shark returned to camera #1 similar to 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 degrees C, which is considerably higher than that of the Greenland shark (similar to 2 degrees 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.