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Look out for the little guys - smaller fish more vulnerable than thought

By Martin Leggett - 02 May 2011 19:0:1 GMT
Look out for the little guys - smaller fish more vulnerable than thought

The shoals of smaller fish swimming at the bottom of the food chain may be more prone to population collapse than previously thought. That's according to a wide-ranging study of 200 scientific analyses, published today in the online Early Edition of Proceedings of the National Academy of Sciences. The evidence of small-fry vulnerability, was fished out by a team led by California's Stanford University. And it runs contrary to the accepted notion that it is the big boys of the marine world - such as shark, tuna and marlin - that are most at risk from man's exploitation of the oceans.

The researchers were looking across the breadth and depth of 50 years of global fisheries data, taking advantage of a new data set - from Dalhousie University, in Halifax, Canada - which was assembled in 2009. When this was combined with scientific assessments on marine ecosystems from the UN's Food and Agriculture Organization, the team had access to a huge amount of information.

From this they hoped to net vital signs of how population crashes are playing out across different types of fisheries - and so perhaps work out the best methods to prevent further collapses of these essential marine resources. Co-author Malin Pinsky said ''We looked at everything from small species to really large species and asked how frequently fisheries collapses occur for the whole range.''

What they found came as something of a surprise. Small fish populations, such as sardines and anchovies, with their rapid life-cycles, have always been thought to have been able to recover from damage faster than larger predatory fish. Previous studies have seen those at the bottom level of the food chain recovering in five years or so. Big fish at the top of the food pyramid can take fifteen years to regain population levels.

But when looking at the whole range of data, and the frequency of fisheries' collapse - as this study has done - it can be seen that it is the small fish that are suffering. They are twice as likely to be hit by major population knock-backs as their bigger brethren. ''We were expecting to see a strong pattern with large, top predators showing the highest probability of collapse,'' said Pinsky, ''We were really surprised to find that just isn't the case.''

That matters because, small fishes are a critical component of the overall food web, one that supports birds and marine mammals, as well as larger fish species. With a relatively low number of species of smaller fry, dramatic falls in populations could eventually produce even bigger waves higher up the food chain. ''There are relatively few species at that level in the food chain, so if one of them collapses, it can have a big impact,'' Pinsky said. ''It is a big deal.''