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close this bookA short review of precautionary reference points and some proposals for their use in data-poor situations (1998)
View the document(introduction...)
View the documentIntroduction
View the documentSome General Considerations
View the documentThe Role of RPs and Harvest Laws in Management
View the documentObjectives Underlying Formulation of Management and Reference Points
View the documentA Brief Classification of LRPs and their Applicability in Information-limited Situations
View the documentFunctioning of an LRP-based System
View the documentSpecific Problems and Approaches for Tuna Fisheries
View the documentReference Points from Size-and-age Data?
View the documentDiagnosis of Areas Where LRPs are Required
View the documentMultispecies RPs?
View the documentSpatial Information and Reference Points
View the documentRotating Closures and Gauntlet Models
View the documentDiscussion
View the documentReferences
View the documentAnnex: Alternative Closed-form Solution for FNOW

Reference Points from Size-and-age Data?

In absence of systematic age reading of, for instance, otoliths, size frequency data may be used to estimate age compositions as a base for VPA or other procedures. In practice, however, this is not extensively done for most oceanic or developing country species or for most invertebrates. It may nonetheless be possible to use catch size composition and growth curves determined from biological sampling or tagging to gain rough estimates of total mortality at age and age/size at maturity. Various common criteria have been proposed for estimating mortality from size compositions (e.g. Sparre et al., 1989) which will not be entered into here, but Die and Caddy (1997) note that combining mortality estimates with size at maturity leads to an LRP criterion in terms of a Z-based LRP, Z*, defined by the inequality or limit:

Z* < K(Linf - Lm)/(Lm - Lc)

where Lm is the mean age at maturity. This inequality seeks to establish a limit in terms of conditions whereby a 50% chance of spawning at least once in the life history is assured, with the implication that, if not respected, due precaution is not being exerted.

The plot of total production against total mortality also yields a useful TRP, the point of Maximal Biological Production, which Die and Caddy (1997) show to be a relatively conservative TRP that corresponds to somewhat lower levels of fishing mortality than at MSY.