LUNAR PERIODICITY IN CATCH RATE AND REPRODUCTIVE CONDITION OF ADULT EASTERN KING PRAWNS, PENAEUS-PLEBEJUS, IN COASTAL WATERS OF SOUTH-EASTERN QUEENSLAND, AUSTRALIA

This study examined the lunar and diel variation in catch rates and re productive condition of adult eastern king prawns, Penaeus plebejus, i n relatively deep (160 m) coastal waters off southeastern Queensland. Females numerically dominated catches over most of the lunar cycle and constituted 76% of the weight of the catch. Analysis of variance (ANO VA) revealed an interaction between lunar phase and sex; catches peake d during Lunar Phase 3 (full moon +/- 3 days) and were particularly ma rked for males. This was the only period during the lunar cycle when t he sex ratio approached 1:1. There was also an interaction between tra wl-time and sex; male catch rates were at a minimum early in the eveni ng, whereas female catch rates were at a maximum then and declined thr oughout the night. Trawler logbook catch rate data from the same area over a similar period indicated an interaction between lunar cycle and lunar phase. ANOVA revealed an effect of the interaction between phas e and sex on the incidence of soft prawns; the incidence of soft males increased during Phase 4 (half moon waning to new moon +/- 3 days). O vary weight also varied between phases and was higher during Phases 2 (half moon waxing to full moon +/- 3 days) and 4 (half moon waning to new moon +/- 3 days). Trends in the ovary weight and the incidence of histologically mature and ripe females suggested there are two periods of increased spawning activity during each lunar cycle. A cyclic regr ession fitted to the data explained 93% of the variation in the incide nce of ripe females between samples. The influence of these cyclic tre nds in catch rate and reproductive condition should be considered when monitoring the spawning stock in the fishery and when planning sampli ng strategies in any future reproductive studies.