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Shrinking fish at risk of being wiped out

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AS FISH get smaller under man's environmental impact they will become more prone to predators and a crucial food source will become more endangered than thought obvious, warn scientists.

Previous research has found some key fish species dwindle in size as larger specimens are trawled out and climate change affects the food chain.

But until now the broader impact of this shrinking has not been explored.

A team from Australia and Finland used computer simulation to predict what might happen should five species of fish decline in average length over a 50-year period.

The shrinkage was quite small, up to 4 per cent. Yet mortality from predators rose as much as 50 per cent, they found.

The repercussions for catches are significant.

Total biomass for four of the species declined as much as 35 per cent, and catches by the same margin, the researchers say in the Royal Society journal Biology Letters.

''Even small decreases in the body size of fish species can have large effects on their natural mortality,'' the team wrote.

The team looked at five southeast Australian trawl fisheries species - jackass morwong, tiger flathead, silver warehou, blue grenadier and pink ling.

Species biomass decreased for all but the grenadier, which also shrank in size but whose numbers actually rose up to 10 per cent as the fish moved to more coastal areas where it was less vulnerable to predators, according to the simulation.

Man is changing marine ecosystems worldwide - directly through fishing and indirectly through global warming, the researchers wrote. ''Fisheries management practices that ignore contemporary life-history changes are likely to overestimate long-term yields and can lead to overfishing,'' they warned.

AFP

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