Growth of juvenile Panulirus longipes cygnus George on coastal reefs compared with those reared under optimal environmental conditions

Abstract

The growth of a group of six juvenile western rock lobsters raised for 6 years in aquaria was well represented by the von Bertalanffy equation

l_t = 113.47{1-exp{-0.459(t-1.045)}]

Using single-moult increments as well as annual growth (determined by shift in modal length and returns of tail-punched and tagged individuals) growth of juveniles in the wild population was compared with that of those reared under near-optimal conditions. At three of the four localities studied, growth was retarded. Growth was most suppressed at the locality where the density of juveniles was highest. However, at a locality where nursery reefs carried relatively low densities in recent years, growth was still well below that achieved in aquaria.

Limited food resources on shallow nursery reefs was suggested as the main reason for the retardation of growth. Where the shortage was less severe, competition amongst juveniles resulted in the growth of younger age-groups (2+ and 3+ years) being more retarded than older juveniles, and that of females being more retarded than that of males. Upon emigrating to deeper waters (mainly at 5 and 6 years of age), juveniles showed a marked acceleration in growth rate. As juveniles have distinct growth phases with different environmental pressures applying at each, growth in the wild population at most localities is not well represented by a single von Bertalanffy equation.