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Fishing Worsens Forage Fish Population Collapses

07 April 2015

US - Fishing has exacerbated collapses in forage fish populations, leading to a need for more sustainable management practices, shows a new study from the University of Washington.

Forage fish include herring, anchovies and sardines.

Some of the largest fisheries in the world target these species, and they are also a key source of food for larger marine animals, including salmon, tuna, seabirds and whales.

Scientists have long known about wide fluctuations in the abundance of forage fish, including the occasional population collapse, so this study set out to determine whether collapses were entirely natural or related to fishing.

Lead author Tim Essington, a University of Washington professor of aquatic and fishery sciences, said: "We've identified the fingerprint of fishing on population fluctuations, finding that fishing makes the troughs of population cycles deeper.

"This is particularly important given the vital role these species play in food webs."

This showed that precautionary management may be particularly important with forage fish, so the researchers used simulations to look at a specific management strategy: suspending fishing when a population falls to less than half of its long-term average.

They found that this strategy would prevent 64 per cent of collapses, but would reduce the average catch by only two per cent over the long term.

"The good news is we find that simple strategies can avoid the worst of the ecological impacts, with little costs to fisheries," Mr Essington said.

"Widespread application of these types of strategies would sustain the benefits people get from forage fish while allowing for sustainable fishing."

Mr Essington and his colleagues reviewed a large global data set of 55 forage fish stocks. Of these, 27 had collapsed at some point, meaning they had fallen to a quarter or less of their average biomass.

To investigate whether fishing was involved, the researchers asked two questions.

First, what was happening before and during the collapse? They found that fishing was particularly intense, about 50 to 200 per cent higher than the average rate. 

Second, do these collapses follow a pattern that would be expected as part of a natural cycle?

To answer this, the researchers compared the forage fish fluctuations to simulations of natural, random fluctuations. 

They found that collapses were more common in the real stocks than in 97 per cent of the simulations, leading them to conclude that fishing is a likely contributor to forage fish collapses.

Forage fish eventually rebound, but the collapses deprive other species of food and fishermen of income for as long as the population is depressed, so management practices to reduce these fluctuations would be beneficial.

Further Reading

You can view the full report and author list by clicking here.

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