CHANGES IN THE SIZE STRUCTURE, SEX-RATIO AND MOLTING ACTIVITY OF A POPULATION OF ORNATE ROCK LOBSTERS, PANULIRUS-ORNATUS, CAUSED BY AN ANNUAL MATURATION MOLT AND MIGRATION

Each spring, most 2-year-old (2+) Panulirus ornatus undergo a maturati on molt and then migrate from the fishing grounds in Torres Strait, wh ich changes the size structure, sex ratio and molting activity of the lobster population. These changes are reflected to varying degrees by changes in the catch of Torres Strait lobster fishermen. The migration begins between early August and early September each year, and depart ure is spread over 4 to 8 weeks. More females migrate than males; thus the sex ratio of the remaining population becomes biased toward males . The maturation molt occurs during one to three peaks in molting acti vity among lobsters about to migrate. These peaks coincide with a gene ral lunar rhythm in the molting activity of the lobster population, wi th peak rates of ecdysis about 1 week after each full moon.