An Alternative Perspective on Recruitment Overfishing and Biological Reference Points

Abstract

Biological reference points are used to guide fisheries management decisions. The reference points most often used are expressed in terms of fishing mortality rate (F). Fmsy relates to the maximization of sustainable yield. In principle, it is a most useful reference point, but in practice it is difficult to estimate. Fmax and F0.1 relate to certain levels of yield per recruit and are easily estimated, but they ignore conservation of the resource. Recruitment overfishing has usually been understood to occur when a population has been fished down to a point where recruitment is substantially reduced or fails. It has not been used as a basis for a biological reference point because the definition is vague and cannot be readily related to fishing mortality. Levels of spawning biomass below which recruitment seems to be reduced have been used, but their determination from available data is usually difficult and controversial. We propose an alternative definition of recruitment overfishing in terms of the level of fishing pressure that reduces the spawning biomass of a year class over its lifetime below the spawning biomass of its parents on average. Conventional models and types of data can be used to determine this level of F, denoted as Frep, which clearly relates to the replacement of spawning biomass and thus to sustainability of a population and yield in the long term.

Beyond connectivity: how empirical methods can quantify population persistence to improve marine protected‐area design

“…1) is correct. It is straightforward, however, to account for density-dependent recruitment (i.e., density-dependent survival of juveniles or larvae recruiting into the adult population) in the persistence criterion (Sissenwine and Shepherd 1987). Even with density dependence, it is ultimately the density-independent survival rate (i.e., the survival rate at very low recruitment) that is important for persistence, because the behavior of the population at low densities is what matters for persistence.…”

This is more difficult than we thought! The responsibility of scientists, managers and stakeholders to mitigate the unsustainability of marine fisheries

“…Values for spawning stock size and recruitment in turn came largely from retrospective analysis using constant parameter values for natural mortality, and often constant values for growth or size-at-age. Thus, RPs based on SRRs constructed from historical SR data, such as F REP (Sissenwine & Shepherd 1987) are only as good as the SRR generating them. It is not intended to criticize this particular RP, just to illustrate that RPs derived from models are not infallible or necessarily better than those obtained using judgement, historical experience and common sense.…”

Population size and exploitation of giant squid (<i>Dosidicus gigas</i> D'Orbigny, 1835) in the Gulf of California, Mexico

“…It is more reliable then to avoid recruitment overfishing, which is defined as the level of fishing pressure that reduces the spawning biomass produced by a year class over its lifetime below the spawning biomass of its parents. Recruitment overfishing, implies exploitation of fishery resource at such an intensive level that compensatory stock responses are insufficient to maintain a normal pattern of recruitment (Overholtz et al, 1986;Sissenwine and Shepherd, 1987).…”