Further Perspectives on Yield per Recruit Analysis and Biological Reference Points

Abstract

Spawner–recruit relationships (SRRs) are indeterminate for most species. Earlier workers proposed solving "amount of harvest" problems for such cases by tacitly assuming that the SRR is density independent (a straight line through the origin) for the available data. I extend that concept and demonstrate a technique for solving "method of harvest" problems when the SRR is indeterminate. This technique uses spawning biomass per recruit, rather than fishing effort, as the benchmark for comparing alternative methods of harvest. Yields from different harvesting methods are deemed comparable only when they produce the same spawning biomass per recruit. If the comparisons are consistent over the entire range of spawning biomass per recruit values, one can evaluate the relative merits of competing methods of harvest without the benefit of spawner–recruit data. Although this technique does not determine the optimal gear selectivity, it allows comparisons of sustainable yields from currently available gear types. The technique is particularly useful for analyzing fishery allocation and by-catch problems. Two life history parameters, critical age (age at which a cohort maximizes its biomass or dollar value) and the age at 50% sexual maturity, may be most important in determining the optimal method of harvest (fishing gear selectivity).