Trends and Dynamics of the Spiny Lobster, Panulirus Argus, Resource in Banco Chinchorro, Mexico

Using information on catch per unit effort, size, and age structure, a suite of quantitative tools were employed to detect trends, and model the dynamics of the spiny lobster, Panulirus argus, resource in Banco Chinchorro without assuming that equilibrium conditions apply. A multiseasonal depletion model was fitted to monthly catch rate (CPUE) data, with catch in numbers and effort measured as fishing trips, for five successive seasons 1988–1989 to 1992–1993. The depletion model captured seasonal and interannual variations of catch rates and provided point estimates of recruitment per fishing season from 43,870–241,150 individuals. The model considered two month-specific values of the catchability coefficient q, whether or not a month showed peaks in catch rate. Monthly fishing mortality rates F were also derived, and F-values per fishing season varied from 0.30–0.38 season⁻¹. These estimates were consistent with those obtained for age-based methods; conversely, they were quite different from those previously estimated by methods assuming equilibrium conditions. Data on commercial size grades were available for two pairs of consecutive fishing seasons, 1983–1984, 1984–1985 and 1989–1990, 1990– 1991. Mean recruitment length to the fishery has declined between 1983–1991. Age-based methods with growth parameters for Cuban lobsters provided total (Z) and by-fishing (F) mortality rates, which also declined over the same period, assuming a constant natural mortality rate (M) applies. Overall, this study suggests that fishing effort and fishing mortality must be maintained at levels closer to those applied in the period 1988–1993. A current issue in population dynamics, namely, open versus closed populations, and their consequences for management and for further research are discussed.