Every year, scientists undertake a programme of work to assess the state of fish stocks in European waters. Marine Scotland Scientists at the Marine Laboratory in Aberdeen collect data on stocks in the North Sea and the West of Scotland. This information is combined with data from other European nations that fish in these waters, and is then considered by the International Council for the Exploration of the Sea (ICES).
ICES estimate the current state of the stock, and forecast what is likely to happen in the future. This process, known as stock assessment, aims to provide fishery managers in the Scottish Government and European Commission with the necessary information on which to base decisions on how much fishing should take place.
Stock Assessment
To determine the 'health' of a fish stock, scientists estimate the following levels:
- Fishing Mortality - A measure of the proportion of a fish stock taken each year by fishing;
- Spawning Stock Biomass - The total weight of mature fish (capable of spawning) in the population, and the minimum weight of mature fish required to ensure a sustainable fishery;
- Recruitment - The number of young fish produced each year which survive from spawning to enter the adult stock and the fishery;
- Landings - The total annual tonnage of fish taken from the stock and landed by the fishing fleet and biological data taken from samples of these landings.
Additional information is collected on when fish spawn, how long they live, what they eat, and changes in the marine environment that may affect fish stocks. The information required to carry out a stock assessment comes from a number of sources including:
- Market Sampling, where information on the length and age of fish is collected at fish markets, along with details of catches of the fishing fleets,
- Discard Sampling, to provide length and age information on fish that are caught that never reach the market. Discard sampling in addition to market sampling provides a complete picture of the effects of fishing on the stocks, and
- Research Vessel Surveys. Surveys provide information on the numbers of young fish (recruits) which are too small to be caught and landed by commercial vessels. They also provide information on changes in the distribution and abundance of the adult stock.