Revisiting taxonomy of cephalopod prey of sperm whales caught commercially in subtropical and Southern Ocean waters

Abstract

The sperm whale is the largest toothed whale that feeds almost exclusively on oceanic cephalopods. Since it was actively hunted commercially, considerably more is known about its food than for many other large marine apex predators. However, the use of those unique dietary information is today hampered by out-of-date cephalopod taxonomy. Here, the names of cephalopod prey of sperm whales were revisited by reviewing taxonomic investigations and tracking over time the names of sclerotized beaks that accumulate in predators’ stomachs. The study focused on the seminal investigations by Clarke (1980) and Clarke and MacLeod (1982), which form the basis of our knowledge on the feeding habits of sperm whales in the Southern Hemisphere. Forty-five different beaks were identified, of which the labelling of 24% taxa is valid today, 7% are still undetermined, and the name of the 69% remaining beaks had to be changed due to improvement in both taxonomy (31%) and beak identification (27%), and to initial misidentifications (11%). Few taxonomic changes occurred at the family level, but changes at the species level are substantial and reveal the dietary importance of poorly known squid species (e.g. Galiteuthis suhmi, Histioteuthis macrohista). Within the southern subtropics, sperm whales feed primarily on five histioteuthids, with Histioteuthis atlantica ranking first numerically, and on octopoteuthids, cranchiids and onychoteuthids. In contrast, whales caught in the Antarctic prey mainly upon three species of Southern Ocean endemics, the cranchiid Mesonychoteuthis hamiltoni, and the onychoteuthids Filippovia knipovitchi and Moroteuthopsis longimana. In conclusion, revisiting taxonomy allowed a better understanding of the deep-sea ecosystem by improving our knowledge on oceanic cephalopods and on the feeding habits of sperm whales, a cephalopod predator that has a key trophic role in the oceans.