Groupers could limit Caribbean lionfish invasion, study reveals
22 July 2011, by Tamera Jones
Groupers could help stem the rapid spread of the invasive lionfish which threatens to wreak havoc across the Caribbean, but only if they're protected from fishing, a study has concluded.
In the Exuma Cays Land and Sea Park – the oldest, largest and 'best-policed' marine reserve in The Bahamas – researchers found ten times fewer lionfish in parts of the reef where there are lots of groupers. Fishing has been banned in the park for 20 years, so it now boasts a healthy grouper population.
But on other reefs where fishing is rife, it's a different story: lionfish populations are exploding.
Lionfish are normally confined to the Indian Ocean and the western Pacific, where they're relatively rare. With colourful but venomous spines, the fish has proved a popular aquarium pet. But at some point in the early 1990s, the fish escaped into the wild; how this happened is a subject of much speculation.
'Where you see plenty of grouper, you see fewer lionfish.'
Dr Alastair Harborne, University of Exeter
Some think aquarium owners decided to release the lionfish when they got too big for their tanks, while others suspect that their eggs escaped somehow. Another idea is that when Hurricane Andrew demolished a Florida aquarium in 1992, a handful of lionfish were accidentally liberated.
Since then, the fish has invaded much of the Caribbean. It's not fussy about what it eats, devouring any small fish in its path. Nor does it care about where it lives, colonising both reefs and mangrove lagoons. This means young reef fish that typically shelter in mangrove lagoons before they set up home on coral reefs don't stand a chance.
'Lionfish appear to be devastating coral reef fish populations in the Caribbean, which could ultimately disrupt coral reef diversity and function,' explains Dr Alastair Harborne, from the University of Exeter, one of the authors of the study.
'They're voracious predators, so scientists are increasingly concerned about the effect they could have. In some experiments, lionfish have led to a 70 per cent reduction in native juvenile fish species,' he adds.
Working out how to control their population is clearly a top priority. Conservationists have taken a number of approaches, like holding harvest days, when locals are encouraged to spear the fish. 'They taste delicious once you remove the spines,' says Harborne.
But people are wary of handling lionfish, because their spines contain a nasty toxin. Instead, throughout the Caribbean, the grouper is the fish of choice. 'It's the cod of the Caribbean,' Harborne explains.
It's not clear which creatures prey on the lionfish in its home territory. But there have been a couple of cases of lionfish being found in the stomachs of Caribbean groupers.
This led Harborne and his colleagues to ask if groupers could be used to control the Caribbean lionfish invasion. Whether or not groupers prey on lionfish to a large enough extent to control the invasive fish isn't obvious. But predatory fishes have been used as pest controllers in other situations.
'The ban on fishing in the Exuma Cays Land and Sea Park gave us the perfect opportunity to ask if these groupers are actually reducing the densities of lionfish in these areas,' Harborne says.
During early summer 2010, the researchers surveyed 12 sites along a stretch of reef in Exuma Cays spanning 30 kilometres. They selected five sites with the marine reserve, and a further seven sites to the north of the park which are fished by locals.
They found more groupers in the Exuma Cays Land and Sea Park than reported almost anywhere else in the Caribbean, with a seven times lower biomass of lionfish within a 30 kilometre stretch of reef. 'Where you see plenty of grouper, you see fewer lionfish,' says Harborne.
But he admits that even when there are lots of groupers, you still get lionfish.
'Lionfish would still spread even in un-fished areas. What we really need is to get a lionfish fishery going in the Caribbean,' he says.
Peter J. Mumby, Alastair R. Harborne, Daniel R. Brumbaugh, Grouper as a Natural Biocontrol of Invasive Lionfish, PLoS ONE 6(6): e21510, published June 23, 2011, doi:10.1371/journal.pone.0021510
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