Manual of indicators and methods for assessing fish stocks using only fishery independent, survey based information

fish stock assessment trawl survey fish survey biological indicator spatial indicator stock status



This manual discusses the use of indicators for assessing the state of a fish stock. The
indicators envisaged are estimated from trawl surveys, or trawl-supplemented surveys such
as egg and acoustic surveys, in which catchability is maintained constant so far as practically
possible. A preliminary section considers factors that determine the appropriateness of a
survey for each species and indicator, and makes suggestions for statistical estimators for
quantitative and descriptive indicators. A widely applicable selection of biological and
spatial indicators is then documented in a standardised format that includes references to
examples of their use and modifications. The biological indicators include those relating to
quantity of fish, , and reproduction. The spatial indicators characterise the geographic
distribution of a stock and make allowance for low or zero densities of fish at some stations.
The final section of the manual presents several presentational and statistical methods for
assessing and interpreting trends in indicators. A stock simulation model is described that
may assist with determination of reference points for biological indicators. Since indicators
tend to be highly specific and normally many would be used to assess the state of a stock,
multivariate methods form an important part of this section. Indicators offer valuable
biological and geographic information for supplementing existing model-based stock
assessments. They are also likely to form an important component of an ecosystem approach
to fishery management, or they could be used pragmatically to tune harvest control rules in a
form of adaptive management.