SEASONAL AND INTERANNUAL VARIABILITY IN KRILL (NYCTIPHANES-AUSTRALIS)STOCKS AND THEIR RELATIONSHIP TO THE FISHERY FOR JACK MACKEREL (TRACHURUS-DECLIVIS) OFF EASTERN TASMANIA, AUSTRALIA

Nyctiphanes australis was collected from the east coast of Tasmania be tween January 1989 and April 1991. Density and biomass were significan tly higher in autumn than in any other season. The population was domi nated by juveniles, except in autumn and spring 1990 when there was a significant increase in the proportion of adults. Our data indicated t hat N. australis does not regularly migrate vertically and that it for ms aggregations of particular size classes which vary both temporally and spatially. Stomach fullness in Trachurus declivis, a major predato r of N. australis, rose to a peak in autumn when N. australis stocks a nd the monthly catches by the fishery for T declivis were at their hig hest. The stomachs of T declivis were also dominated by adult size cla sses during this period. The virtual absence of N. australis in 1989 a nd the subsequent failure of the T declivis fishery in that year under line the interrelationship between these two species. We suggest that this was the result of an influx of subtropical northern waters low in nutrients onto the shelf, which corresponded with a major La Nina ''c old event'' at that time.