DNA suggests marine reserves boost commercial fishing

If you protect fish, there will be more of them to catch. That's the reasoning conservationists have long used to persuade commercial fisheries of the benefits of marine reserves. Now they may have DNA confirmation.

Earlier research had shown that marine reserves result in larger fish that spawn more offspring, but researchers were left speculating exactly where the baby fish ended up and whether they truly help replenish other areas.

Now, with the use of new DNA profiling techniques, scientists have shown that by devoting less than a third of an area to a marine reserve network, you can double the number of juvenile fish that settle in the rest of the area. (Current Biology, DOI: 10.1016/j.cub.2012.04.008)

Garry Russ, one of the authors of the study, said he has spent the last 30 years contemplating how you can confirm exactly where fish born in marine reserves go. "To me, it's a little bit like the holy grail of marine reserves as fishery management tools," he says.

To nail the problem, Russ and colleagues at the ARC Centre for Excellence for Coral Reef Studies in Queensland, Australia caught 1620 adult coral trout and stripey snapper from a series of reserves on the Great Barrier Reef. Both species are popular with commercial and recreational fishing. They then took DNA samples from their tails, and released them alive. Later, they sampled juvenile fish from 19 locations throughout the region and checked to see if they were offspring of the fish in the reserves.

Though the reserves make up just 28 per cent of the area, the team calculated that about half of all juvenile fish were spawned by fish in the reserves ? showing that the protected areas "punch above their weight in replenishing fishery stocks", as Russ puts it.

But fisheries ecologist Colin Buxton from the University of Tasmania at Sandy Bay in Tasmania, Australia isn't convinced that these results show reserves will help commercial fisheries. If the adult population isn't suffering from a shortage of juvenile fish ? as he says is the case in the area studied ? then introducing more young fish won't help.

Buxton adds that the only effective way to maintain sustainable fish populations is to limit the number of fish taken out of the water.

Yet Russ believes the new findings provide strong evidence that marine reserves are a useful tool in maintaining fish populations. "Doubling the number of recruits coming into a population is almost always going to affect the adult population size quite substantially," he says.

Russ and his team next plan to look at the genetic makeup of the fisheries' catches to see if they are in fact being bulked up by fish breeding in the reserves. Their future research will also require them to cast a wider net ? to see just how far from the marine reserve fish spawned there will travel.

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