Population ecology and fishery potential of the spiny lobster Panulirus penicillatus at Enewetak Atoll, Marshall Islands

The spiny lobster, Panulirus penicillatus, was studied at Enewetak Atoll during 1978–1979 to evaluate aspects of population ecology and fishery potential. Declining catch/effort was used to estimate a total population at risk of 5,500 individuals during August–September 1979 for the windward half of the atoll. Number caught per man-h⁻¹ was highest on the northern reefs (ca. 4 ± 1 (SE)) and lowest on the southern reefs (ca. 2 ± 1 (SE)). The sex ratio was skewed, with 71% females out of 791 lobsters collected during the study. Lobsters were tagged with a coded pattern of holes punched in the telson segments and change in carapace length of tagged individuals was used to estimate parameters of the Brody-Bertalanffy growth equation: S_max = 146.5 mm and K = 0.211 yr⁻¹ for carapace length of males and S_max = 96.5 mm and K = 0.580 yr⁻¹ for females. The natural mortality rate coefficient, M, is 0.284 yr⁻¹ for males and 0.244 yr⁻¹ for females; about 25% mortality per year. A dynamic-pool model was used to evaluate characteristics of yield related to potential fishing intensity. Maximum yield per recruit would be with a fishing rate coefficient, F, of about 0.5 to 0.6, which would yield an average weight of lobsters of about 450 g. Radionuclide levels in the muscle are low and lobsters from the windward reefs of Enewetak would be acceptable for human consumption. We conclude that P. penicillatus could support a modest fishery that would yield about 1 metric ton (total wet weight) per year for the windward half of the atoll.