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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