Predation on the St Joseph Callorhinchus capensis by Cape fur seals Arctocephalus pusillus pusillus in Namibia

Abstract

Chondrichthyans form an important part of marine food webs as top predators and mesopredators. However, little is known about chondrichthyans in Namibian waters and the roles they play in ecosystem function. During efforts to disentangle Cape fur seals Arctocephalus pusillus pusillus from fishing gear or plastic debris, 11 incidents of seals impaled by the dorsal spines of St Josephs Callorhinchus capensis (order Chimaeriformes) were recorded. These observations overlapped with mass die-offs of the seals owing to food shortages, as indicated by large numbers of emaciated seals and widespread miscarriages of seal foetuses. This suggests that the St Joseph is not a desirable prey species for Cape fur seals, though this chimaera may provide a source of food, especially when preferred prey species are unavailable. This is the first published record of Cape fur seals feeding on chondrichthyans in Namibian waters. Documenting these types of food-web linkages between pinnipeds and chondrichthyans will allow for a better understanding of how impacts on their populations may more broadly affect Namibia’s marine ecosystems.