REPRODUCTIVE TRADE-OFF IN MALE ANTARCTIC KRILL, EUPHAUSIA-SUPERBA

Freshly caught male and female Euphausia superba from the same swarm e xhibited different rates of mortality subsequent to capture. Mortality was significantly higher for reproductive males (100%, n = 68) than f or females (3%, n = 186) within the first 3 d of capture. Total lipid and triacylglycerol levels in male, female and juvenile Euphausia supe rba were analysed and compared. All reproductive male krill analysed f rom this swarm had low lipid levels (1 to 3% dry weight) with negligib le triacylglycerol stores (0 to 2% of total lipid). Somatic lipid stor es in female and juvenile krill ranged from 8 to 30%, of which up to 4 0% was triacylglycerol. The levels of algal sterols in the digestive g land of males, females and juveniles indicate that all krill had been feeding recently. An analysis of the sex ratio of krill catches derive d from data collected over seven summers from the Prydz Bay region sho wed a decrease in the proportion of males with increasing size. There was a sharp decline in numbers of male krill once they attained a leng th of 51 to 55 mm. Low lipid levels in redroductive male krill may be due to reproductive costs. The resulting low storage-lipid levels are accompanied by high mortality in male krill.