KRILL CAUGHT BY PREDATORS AND NETS - DIFFERENCES BETWEEN SPECIES AND TECHNIQUES

Samples of Antarctic krill collected from 6 seabird species and Antarc tic fur seal during February 1986 at South Georgia were compared to kr ill from scientific nets fished in the area at the same time. The leng th-frequency distribution of krill was broadly similar between predato rs and nets although the krill taken by diving species formed a homoge neous group which showed significant differences from krill taken by o ther predators and by nets. There were significant differences in the maturity/sex stage composition between nets and predators; in particul ar all predator species showed a consistent sex bias towards female kr ill. Similarities in the krill taken by macaroni (offshore feeding) an d gentoo (inshore feeding) penguins and differences between krill take n by penguins and albatrosses suggest that foraging techniques were mo re important than foraging location in influencing the type of krill i n predator diets. Most krill taken by predators were adult; most femal e krill were sexually active (particularly when allowance is made for misclassification bias arising from predator digestion). Because femal e krill are larger, and probably less maneuverable, than males, the bi ased sex ratio in predator diets at this time of year may reflect some combination of selectivity by predators and superior escape responses of male krill. Overall, adult, sexually active female krill, forming 40% by number of the local krill population, may comprise 60 to 70% by number and 75 to 88% by mass of the krill taken by their main seabird and seal predators at South Georgia al the time of peak local demand in February.