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Northern range extension and genetic validation of the Antarctic sleeper shark Somniosus antarcticus (Somniosidae) in northern Chile

aquaculture-fisheries-and-fish-science
biogeography
conservation-biology
marine-biology

Abstract

Sleeper sharks (family Somniosidae) are large, slow-growing deep-sea sharks with poorly resolved taxonomy. Within the genus Somniosus, the large-bodied subgenus Somniosus includes S. microcephalus, S. pacificus and S. antarcticus. In the southeastern Pacific, records from Chilean waters have usually been attributed to S. pacificus or Somniosus cf. pacificus, but have seldom been supported by detailed morphological or genetic data. Here we report the first confirmed record of Somniosus antarcticus from northern Chile, based on an adult female and a near-term male pup incidentally captured by a deep-sea longline fishery off Antofagasta (22°15′S, 70°45′W) at ~1000 m depth in 2023. The pup was preserved whole and examined using 64 morphometric characters, tooth counts, dermal denticles and spiral valve turns. It showed a cylindrical body, short rounded snout, spineless dorsal fins, hook-like dermal denticles, and a 40-turn spiral valve that characterizes S. antarcticus and distinguishes it from small-bodied Rhinoscymnus species. Genomic DNA was extracted from the pup and from the caudal fin of the presumed mother. A 639 bp fragment of the mitochondrial COI gene was sequenced for both individuals; the sequences were identical and matched reference Somniosus sequences from Antarctica and New Zealand with ≥99.7% similarity. Phylogenetic analysis placed the Chilean haplotype within a Southern Hemisphere Somniosus clade, consistent with S. antarcticus sensu Yano. This record extends the confirmed distribution of S. antarcticus in the southeastern Pacific by approximately 1350 km northward, provides the first verified small male from Chilean waters, and highlights the need for integrative morphology–molecular approaches to document deep-sea shark bycatch and clarify species boundaries in Somniosus. Similar interactions with sleeper sharks have been documented in the same Patagonian toothfish longline fishery in austral Chilean waters, suggesting that Somniosus spp. may be a more widespread component of deep-sea bycatch than currently reported.
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