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A new study has shown that it is not just the big fish that matter in marine ecosystems and that catches should be cut in order to safeguard marine fish stocks.

The study which was funded by the Marine Stewardship Council (MSC) and lead by an international team of scientists found that fishing methods that remove smaller fish can have severe impacts on their ecosystems.

Anthony Smith and colleagues looked at five different ecosystems around the world and subjected species at the bottom of their food chain such as krill, anchovies, herring, mackerel, sardine and capelin to varying degrees of fishing pressure.

They found that fishing the most plentiful fish in an ecosystem, or the ones that are most highly connected in the food web, tends to have the largest impacts on those ecosystems, having a knock on effect on mammals, seabirds, and larger fish.

At present around 30% of the global fishery production comes from smaller fish where they are used to produce fishmeal and also as a food source especially in the developing world.

The study used computer modelling on fish in Peru, Australia, southern Africa, the California current and the North Sea. It showed that harvesting these fish at the so-called 'maximum sustainable yield' had significant effects and as much as a 60% change in biomass could be seen in some ecological groups when there was just a 25% decrease in the numbers of the smaller (lower trophic level) fish.

The team suggested that catches should be severely cut and in places backed up by no-fish zones such as seen in the North Sea where fishing of sand eels is banned to protect breeding sebirds.

By halving the exploitation rates of certain low-level species, Smith and his colleagues say that fisheries could still achieve 80% of their maximum sustainable yields while also lessening the impact on marine ecosystems. This in turn may bring associated long-term economic benefits as well as the recovery of some larger fish species which have been depleted by over-fishing.

Their findings should help to inform harvest strategies that could ensure that fisheries maintain substantial yields while also protecting ecosystems from collapse.

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