High mortality of adult female Magellanic penguins by gillnet fisheries in southern Brazil

Bycatch in gillnet fisheries is one of the main threats to several penguin species. Magellanic penguins (Spheniscus magellanicus) are caught by gillnets during their wintering in southern Brazil. However, current information is based only on a small number of sets observed during a single fishing trip. This study assesses bycatch rates of bottom and drift gillnets operating in southern Brazil, and describes the sex and age classes of individuals captured. In 80 bottom gillnet sets, 33 penguins were captured (85% adults), 14 were sexed of which 13 were females. In 41 drift gillnet sets, four penguins were captured, three of which were juveniles. The mean bycatch rates, measured as number of penguins km(-2) of net and number of penguins km(-2) h(-1), were significantly higher for the drift gillnets. Despite the lower bycatch rates, owing to the higher fishing effort in terms of number of boats, net length, net area, soak time and fishing season, the magnitude of penguin bycatch in the bottom gillnet fishery cannot be ignored. Despite based on small sample size, the predominance of adult and female Magellanic penguins as bycatch in gillnet fisheries in southern Brazil agrees with previous studies suggesting that females displace further north than males. In addition, such evidence contributes to the male-biased sex ratio in breeding grounds, and the long-term decline of major Patagonian colonies owing to higher female mortality during winter.