Groupers help cull lionfish


Since venomous lionfish
began invading Cayman’s reefs back in early 2008, divers have seemed to be the
only line of defence against them, but groupers are now joining the fight.

On Little Cayman, dive
masters have begun feeding lionfish to groupers and hope the large fish will
teach other groupers to do the same.

It started with the divers
feeding dead lionfish to the tame Nassau groupers that interact with divers at
Bloody Bay Wall, explained dive master Ron Thompson at Little Cayman Beach
Resort’s Reef Divers.

“In the beginning, we fed
our friendly groupers, mainly Benji and Mini-Me, the dead lionfish that we had
previously caught and killed. The instructors would… take the nets down with
the dead lionfish and open the bags up when the groupers came to see us.

“Once they got used to the
idea of dead lionfish, we then progressed to live lionfish from the nets,” Mr.
Thompson said.

“Even more recently, they
have started to take live lionfish from the reefs if the dive masters point
them out,” he said.

He explained that prior to
trying to teach groupers that lionfish were a tasty snack, the dive masters had
never fed the groupers anything.

“Groupers have a nuclear
hunting behaviour with other creatures, such as moray eels. They hunt together.
The groupers use us as hunting partners as we used to point squirrelfish out to
them to hunt,” he said.

However, despite the fact
that the groupers are eating lionfish pointed out by divers, it is not known if
they are taking the spiny, poisonous lionfish of their own accord, without
divers pointing to them, but Mr. Thompson said he believed it was quite likely.

“Groupers are quick to learn
and often mimic the behaviours of other groupers,” he said.

The Marine Conservation Law
was amended following the arrival of the invasive lionfish in Cayman to allow
divers to hunt and remove them from the reefs. Lionfish have voracious
appetites and can wipe out juvenile and small fish species on a reef in just

Department of Environment
staff say it is vital to control the lionfish population because the fish can
lay 30,000 eggs in one spawn and they can spawn every month. The department has
been running a series of seminars to educate people about lionfish and certify divers
to catch them.

The courses teach divers how
to locate and capture lionfish in clear, plastic nets without getting stung,
and what to do if they are stung.

And even though lionfish
stings are extremely toxic to humans, the groupers do not seem to suffer any
ill effects from ingesting the fish. “If fact, the Nassau groupers now get very
excited if they see the dive masters coming with a net with their new tasty
treat,” said Mr. Thompson.

Dive masters on Little
Cayman have also been feeding dead lionfish to other marine species, including
green, spotted and viper morays, octopi, lobsters and reef sharks.

“While we do try and catch
as many lionfish as we can, we are trying to promote the groupers and other
marine life to hunt them as well. It may take time but we are trying to find a
natural solution to this problem,” Mr. Thompson said.

Mark Hixon, a marine biologist
at Oregon State University, who has visited Little Cayman twice this year to
study the impact of the lionfish, said he hoped the groupers would teach each
others by example to consume the invaders.

But he said that, for now,
divers culling lionfish is the best means of keeping their numbers down.

“Culling is very effective over
small areas, but complete eradication is unlikely unless natural controls –
predators, competitors, parasites, diseases – kick in,” he said.