Revealing stock–recruitment relationships in lobsters and crabs: is experimental ecology the key?

Abstract

As is true for many fish and invertebrate fisheries, stock–recruitment relationships remain poorly understood for most commercially important species of lobsters and crabs. This paper gives a critical overview of advances in assessing the relative importance of pre- and post-settlement processes to the recruitment of 14 commercially and/or ecologically important lobsters and crabs. Three case studies (western rock lobster, Panulirus cygnus, blue crab, Callinectes sapidus, and the American lobster, Homarus americanus) are used to illustrate where standard fishery survey methods, combined with field experiments, have provided insights into the form of stock–recruit relationships and the ecological processes that influence them. It is notable that larval supply-dominated cases, such as that of P. cygnus, may be less common than those dominated by post-settlement processes, such as C. sapidus, in which strong compensatory processes lead to non-linear spawner-to-recruit or juvenile-to-recruit relationships. In other cases, such as H. americanus, the influence of post-settlement controls remains controversial. Significant settler or juvenile-to-recruit linkages have been reported more often than spawner-to-recruit relationships, most likely because pre-settlement processes often mask the latter. Innovative field experiments, early life stage monitoring and spatial modeling have improved our understanding of the influence of competition, predation, cannibalism, sociality and movements to the demography of some of these species. Field experiments have been more widely used by American and Australian than European investigators. Ecological experiments are not a panacea, though, and can lead to misinterpretation, especially of the relative importance of mortality and emigration. Uncertainties about age and the relevant spatial scale at which to evaluate stock–recruitment relationships have posed further challenges. This review underscores the need to design ecological studies at a geographic scale that will better reveal the stock–recruitment relationship.