A COMPARISON OF ANTARCTIC KRILL EUPHAUSIA-SUPERBA CAUGHT BY NETS AND TAKEN BY MACARONI PENGUINS EUDYPTES-CHRYSOLOPHUS - EVIDENCE FOR SELECTION

Using stomach lavage samples from macaroni penguins Eudyptes chrysolop hus Brandt breeding at Bird island, South Georgia and concurrent net s amples caught within the penguin foraging range, we examined the poten tial selection of different length and maturity stages of Antarctic kr ill Euphausia superba Dana. Using Monte Carlo randomised simulation te chniques, we also determined the probability of obtaining length-frequ ency distributions of krill different from that obtained in the net sa mples. The krill taken by the macaroni penguins differed significantly from those caught in the nets. Small krill (28 to 38 mm) were absent from the stomach samples, whereas large krill (58 to 62 mm) were more abundant. Random sampling using Monte Carlo simulation techniques prod uced length-frequency distributions that were statistically different from the original distribution of krill caught in nets on 76 out of 10 0 trials. Nevertheless, these differences were smaller than those foun d between the penguin samples and net samples. Comparison of krill mat urity stages showed that krill taken by macaroni penguins contained 3 times as many female as male krill, whereas krill caught in nets conta ined nearly equal proportions. The differences in size and maturity of krill taken by penguins are discussed in terms of aggregated random s ampling, prey selection by predators, and evasion by krill of predator s and nets. We conclude that the differences are unlikely to be accoun ted for simply by sampling anomalies; the differences are more Likely to relate to penguins selecting larger, nutritionally superior krill, but might also reflect differential escape responses of particular cla sses of krill when evading penguins or nets.