Reproduction, abundance and feeding habits of the broadnose sevengill shark Notorynchus cepedianus in north Patagonia, Argentina

Abstract

Broadnose sevengill sharks Notorynchus cepedianus caught in a recreational fishery during a 3 yr period in Anegada Bay, Argentina were examined. Monthly variations in abundance were found, with the highest mean abundance in April. Neonates and juveniles were common in the study area, indicating that Anegada Bay is a nursery area of N. cepedianus. Male and female sizes at maturity were 170 and 224 cm total length (TL), respectively, similar to other studied regions. Liver size was sexually dimorphic, with adult females having larger livers, which might allow for the max- imization of oocyte size/number. Individuals 170 cm fed mostly on carti- laginous fishes and marine mammals. All size groups preyed on marine mammals, which may be a result of the local availability of small calves of La Plata River dolphins Pontoporia blainvillei. Possi- bly, the pattern of habitat use of Anegada Bay by P. blainvillei is affected by N. cepedianus. The pro- portion of individuals with prey within the stomach was negatively correlated with TL. As indicated by prey remains found within stomachs (most were in pieces) and by the location of the fishing hook in sharks (most were hooked in the mouth), N. cepedianus extensively handles its prey with the mouth before swallowing it, which is consistent with previous observations. Anegada Bay may be an important area for conservation of N. cepedianus in the SW Atlantic given the high abundance of juveniles and subadults.