Diet overlap among top predators at the South Orkney Islands, Antarctica.

BERTOLIN M.; CASAUX R.

Workshop; The CCAMLR Ecosystem Monitoring and Management Working Group; 2018

AbstractIn order to understand interspecifictrophic relationships among top predators, we analyzed diet information on nine bird and two seal species collected inthe austral summer from 1996 to 2000 at South Orkney Islands. Overall, the dietof most of the predators was mainly composed of krill, fish or penguins. There-occurrence of prey among predators was intermediate and ranged from 25.3 to 36.7and fish, krill and squid re-occurred most frequently. The re-occurrence offish among predator pairs was low and ranged from 8.1 to 28.1. The species thatre-occurred most frequently were the nototheniids Gobionotothen gibberifrons, Nototheniopsnudifrons and Nototheniops nybelini,and the myctophid Electrona antarctica.Prey overlap was greatest between Chinstrap and Adélie penguins. Most predatorpairs had high overlap of fish prey. Predators that could forage on demersal orwater column prey had yearly variable diets. This variability may be explained byfluctuations in krill availability. In years when krill is scarce (e.g. 2000),these predators can diversify their diet by increasing the consumption of fish,which increases the re-occurrence of these preys in the diets. Our samples suggestthe recovery of G. gibberifrons stocksaround the South Orkney Islands and draw the attention to the potential increaseof interspecific food competition among predators under scenarios of decreasingkrill availability.