Variability in the population structure of Lutjanus adetii (Castelnau, 1873) and L-quinquelineatus (Bloch, 1790) among reefs in the central Great Barrier Reef, Australia

The recent age validation of the tropical snappers L. adetii and L. quinquelineatus has facilitated the comparison of growth, mortality, and age structures for both these species at the spatial scale of individual reefs. The age structure of both species among reefs within the Great Barrier Reef Marine Park was based on counts of annuli from sectioned otoliths. There was significant variability in growth, mortality, and age structures. Significant differences in mean length, age, and weight (independent of the sex of the fish) were observed for both species among reefs. Peaks in abundance of year classes were variable from reef to reef. Comparisons of the von Bertalanffy growth curves indicated that the pattern of growth in individuals of L. quinquelineatus was significantly different among reefs, whereas the pattern of growth in L. adetii was not. However, there were no significant differences in the mean length of the early age classes of either species among reefs. The mortality rates and hence survivorship of both L. adetii and L. quinquelineatus among reefs were highly variable. It is hypothesized that the varying age structures and mortality rates of both of these species at the spatial scale of individual coral reefs are determined by the nonequilibrial balance of variable recruitment interacting with density-independent mortality. Hence the effect of good recruitment years may persist in the age structure of populations over time.