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Why stock assessment matters
Scientific advice typically guides appropriate catch or fishing-effort levels. It may also cover fishing-gear types and designs, closed areas, and closed seasons.
Scientists produce stock assessments through intergovernmental science organisations such as ICES and ICCAT. These assessments provide the basis for advice to fisheries managers.
What is a stock?
A fish or shellfish stock is a population of one species with common biological, migratory, reproductive, and genetic characteristics.
Some stocks are highly migratory and cover large areas, such as mackerel in the Northeast Atlantic. Others are more localised, such as haddock in the Irish Sea. Stocks of the same species can also overlap in space and time, as occurs with herring and monkfish.
Evidence used in stock assessments
Scientists combine biological, catch, and survey information to understand stock size, structure, distribution, and development.
Biological characteristics
Scientists examine growth rates, age at maturity, and natural mortality. Natural mortality includes deaths from causes other than fishing, such as predation and disease.
Commercial catch information
Landings and discarded unwanted catch show what fishing removes from a stock. Age-based sampling helps scientists assess individual year classes or cohorts.
Research surveys
Research-vessel surveys provide information on stock size, structure, distribution, and biology. Methods include acoustic, trawl, and underwater television surveys.
From assessment methods to scientific advice
Scientists benchmark the method for each stock, usually every three to five years. The selected method reflects the amount of information available. They generally update assessments annually with the latest data and use mathematical and statistical population models to combine the datasets. The results show how a stock has developed over time and support advice consistent with conservation and fishery objectives.