Southern sleeper shark

It was formerly sometimes viewed as conspecific with either the Greenland shark (Somniosus microcephalus), or the Pacific sleeper shark (Somniosus pacificus).[3]

It is known from depths of 400 to 1,100 m.[1][4]

Its length is up to 4.4 m (14 ft).[4] The southern sleeper shark differs from S. microcephalus in having more tooth rows in the lower jaw, a shorter interdorsal region, a more posterior first dorsal fin, and fewer precaudal vertebrae, and from both species in having lower dorsal fins.[3]

It feeds primarily on cephalopods, especially squid — including the giant and colossal squids — and fish; its stomach contents also less commonly contain remains of marine mammals and birds.[1] Based on its generally sluggish nature and the speed of its prey, it is thought to be an ambush predator.[1] A 3.6 m (12 ft) long female caught off the coast of Chile had a whole southern right whale dolphin in its stomach. This dogfish is sometimes taken as bycatch in the orange roughy and Patagonian toothfish fisheries; whether this poses a threat to the species is currently unknown.[1]

In June 2018 the New Zealand Department of Conservation classified the southern sleeper shark as "Not Threatened" with the qualifiers "Data Poor" and "Uncertain whether Secure Overseas" under the New Zealand Threat Classification System.[5] The IUCN also does not regard it as threatened, noting a widespread distribution and no indication of a declining population, but believes it is not naturally abundant and that much more data and understanding of its population, interactions and biology is needed.[1]