Implications of protracted recruitment for perception of the spawner-recruit relationship

In European lobster, Homarus gammarus, wide growth variation means that ann ual recruitment to a fishery (individuals reaching legal size in the same y ear) consists of at least six year-classes (individuals hatching in the sam e year). In this paper, a simple simulation analysis is used to explore the effects of uncertainty about the specifics of this protracted recruitment pattern on the way that we perceive the spawner-recruit relationship. In th e simulation, if the age range of recruits is underestimated or a simple co rrection for growth variation is applied by averaging numbers of recruits a cross years, a spawner-recruit relationship with artefactual curvature and noise arises. Growth variability is typical in animal populations and probl ems with protracted recruitment may occur in any situation where recruitmen t is based on size. Asymptotic spawner-recruit curves may not necessarily r eflect density-dependent compensatory mortality and resilience to harvestin g. The evidence presented here has important management implications for lo bster and other exploited species.