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

NELSON BOVCON; ALEJO J. IRIGOYEN; DE WYYSIECKI AGUSTIN; TROBBIANI GASTÓN; AWRUCH CYNTHIA; ARGEMI FEDERICO; JAUREGUIZAR ANDRES

Conferencia; Sharks International Conference; 2018

Understanding patterns of habitat use and seasonal dynamics of marine species, and gaining insight on how they relate with the environment and other members of the community is critical for their management. This study investigates the habitat use, seasonal patterns of abundance and population structure of the broadnose sevengill shark, Notorynchus cepedianus, in a marine temperate environment of a northern Patagonian bay (Argentina).A suit of baited remote underwater video stations (BRUVS) derived and catch-and-effort data indices were constructed to estimate the seasonal abundance of the species inside the bay. Reproductive hormone levels were used to determine reproductive status and maturity stages of the population. Results indicated that N. cepedianus uses the bay year-round, with a peak of abundance during the spring season when the species aggregates. This peak of abundance coincides with the presence of mature adults, a high frequency of regurgitation of pieces of southern elephant seal (Mirounga leonina), and the presence of mating scars on large females suggesting that sevengill sharks aggregate in Caleta Valdés with feeding and mating purposes. In this time of the year, elephant seals arrive to Valdés peninsula to breed and moult, and by late spring pups get into the sea for the first time and hence are vulnerable to predation by sharks. Male and female sizes at maturity occurred at 170 and 190 cm of total length respectively. Conversely to other studies in the Southwest Atlantic, population composition remained similar throughout the seasons with adult individuals dominating over juveniles and adult females prevailing in the population at all times. All recaptures (~7%) occurred inside the bay suggesting both long- and short-term site fidelity in the timescale covered by the study (i.e. between field trips, and seasons). Considering the historical abundance decline recently reported for the species, protection and enforcement within protected areas across the Southwest Atlantic must remain as high priority action in government initiatives.