The Optimal Recovery of a Semelparous Fish Population with Delayed Recruitment

Research PaperAnnual recruitment of the New Zealand longfin eel (Anguilla dieffenbachii) has decreased by around 75 percent since heavy levels of commercial fishing began in the early 1970s. Given the unsustainability of existing regulatory policy, a deterministic multiple-cohort bioeconomic model is developed and applied to this system to gain insight into the optimal age structure and harvest profile for this species. This model illustrates that the rapid recovery of this fishery would rely on the ability of managers to sufficiently limit the harvest of more valuable year classes to allow for the rebuilding of spawning biomass. The importance of decreasing the degree of exploitation within the fishable population and lessening the time that longfins are available to harvest through higher minimum weight restrictions is also highlighted. The need for conservative management is reinforced when uncertainty regarding the effect of exploitation on fecundity and barriers to the successful instigation of these policies are considered