Changes in maturation ages and sizes in crustacean and fish populations

The relationships between growth rates, fecundity and lengths and ages at sexual maturity are explored, with examples primarily in spiny lobsters, to illustrate the underlying principles involved. Changes in the dynamics of exploited populations of both fish and crustaceans often have important implications for egg production. Two independent processes are thought to be involved, genetic changes caused by the removal of certain genotypes by size-selective fisheries, and growth changes caused by altered stock densities and/or changed food availability. The impacts of these processes on maturity length appear to be antagonistic, giving rise to some contradictory effects in different exploited stocks, some stocks exhibiting increases and others showing decreases in length at maturity.