A short review of precautionary reference points and some proposals for their use in data-poor situations (1998) |

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(L_{inf}- L_{m})/(L_{m}- L_{c})

where L_{m} 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.