Habitat use, seasonality and demography of an apex predator in a marine temperate environment: the case of the sevengill shark Notorynchus cepedianus in northern Patagonia

Gaining insight on how species relate to the environment and other members of the trophic community is critical for their management. This study investigated habitat use, seasonal patterns of abundance and population structure of the broadnose sevengill shark Notorynchus cepedianus in the marine temperate environment of a northern Patagonian bay (Argentina). We expected N. cepedianus to exhibit strong seasonality in the bay driven by the seasonal occurrence of important marine mammal prey. However, an alternative or complementary hypothesis could be related to the possibility that N. cepedianus uses the area seasonally as mating grounds. To explore these hypotheses a suite of baited remote underwater video stations and catch and effort data indices were used to estimate the seasonal relative abundance of the species inside the bay. Reproductive hormone levels were employed to determine reproductive status and maturity stages of the population. Results indicated that N. cepedianus uses the bay year-round, showing a peak of abundance during spring when the species aggregates, likely for feeding and mating purposes. Male and female sizes at maturity occurred at 170 and 190 cm of total length, respectively. Contrary to other studies in the Southwest Atlantic, population composition remained similar throughout the seasons, with adults dominating over juveniles and adult females prevailing in the population at all times. Considering the historical abundance decline recently reported for the species, protection and enforcement within protected areas across the Southwest Atlantic must remain of high priority in government initiatives.

Palabras clave
Baited remote underwater video station
Catch per unit effort
Caleta Valdés