Habitat use, seasonality and demography of an apex predator: sevengill shark Notorynchus cepedianus in northern Patagonia

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

MARINE ECOLOGY PROGRESS SERIES

INTER-RESEARCH

Lugar: Oldendorf/Luhe; Año: 2018

0171-8630

Gaining insight on how species relate to their environment and other members of thetrophic community is critical for their management. We investigated habitat use, seasonal patternsof abundance and population structure of the broadnose sevengill shark Notorynchus cepedianusin the marine temperate environment of a northern Patagonian bay (Argentina). We expectedN. cepedianus to exhibit strong seasonality in the bay driven by the seasonal occurrence of importantmarine mammal prey. However, an alternative or complementary hypothesis arose from thepossibility that N. cepedianus uses the area seasonally as mating grounds. To explore these hypo -theses, a suite of baited remote underwater video stations and catch per unit effort data indiceswere used to estimate the seasonal relative abundance of the species inside the bay. Reproductivehormone levels were measured to determine reproductive status and maturity stages of the population.Results indicated that N. cepedianus uses the bay year-round, showing a peak abundanceduring spring when individuals aggregate, likely for feeding and mating purposes. Male andfemale total lengths at maturity were 170 and 190 cm, respectively. Contrary to other studies in theSouthwest Atlantic, population composition remained similar throughout the seasons, with adultsdominating over juveniles, and adult females prevailing in the population at all times. Consideringthe historical abundance decline recently reported for the species, protection and enforcementwithin protected areas across the Southwest Atlantic must remain of high priority in governmentinitiatives.