Destructive lionfish are invading coral
reefs in the Americas, but fishing competitions can help to keep the
problem species in check.
12 September 2014
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| Pterois volitans - Green Photo Archive |
Stephanie Green plunged her hands,
sheathed in thick black gloves, into a cooler full of lionfish.
Skilfully avoiding its 18 venomous spines, she plucked one out
and laid it on a table to record its length. Nearby, volunteers were
chopping up the brown, red and white striped fish to make ceviche and
passing the dish into the crowd.
As they nibbled on the food, teams of
scuba divers milled around the scoring area. They checked out each
other’s catches and argued over who would be taking home the more
than US$3,500 worth of prizes from the 2013 lionfish hunting derby in
Key Largo, Florida.
“At the check-in time it’s a mad
rush, with teams coming in with coolers of fish, trying to beat the
clock,” says Green, the chief scientist of the contest and a marine
ecologist at Oregon State University in Corvallis. By the end of that
day last September, Green and the other scorekeepers had counted 707
lionfish, from one smaller than a golf ball to one that stretched
nearly two soccer balls long.
The hunting
competition is part of an effort to tackle an invasive species that
has been identified as one of the world’s greatest conservation
issues1. Since lionfish (Pterois volitans) first appeared on the
eastern seaboard of the United States in the 1980s, the voracious
predators have gobbled up coral-reef fish from North Carolina to
Venezuela. Officials responsible for protecting reefs have struggled
to find ways to control populations, and managers are embracing these
fishing contests in a handful of coastal communities.
The strategy is a bit of a gamble,
given that competitions to catch other invasive species — such as
pythons in Florida — have had limited success. But the data
collected by Green show that even one-day contests can effectively
knock down local populations. Her findings and those from other
hunting efforts offer lessons on how a little bit of reward money —
coupled with science and outreach — can help to keep invasive
species in check. “We can’t control lionfish in the entire ocean,
but derbies can have high impacts locally,” says James Morris, an
ecologist with the US National Oceanic and Atmospheric Administration
in Beaufort, North Carolina.
Like many
invasions, the lionfish conquest started small. The fish are normally
found in the western Pacific Ocean, Indian Ocean and Red Sea, where
predators and competitors keep the populations under control. Genetic
analysis2 suggests that roughly a dozen fish were first
introduced off the Florida coast, either accidentally or
intentionally released from aquariums. From there, the population
exploded. Lionfish spawn almost continuously, releasing 2 million
eggs a year, and they have few predators or competitors in their new
home.
“At first people thought they were
funny, beautiful,” says Mark Vermeij, a conservation biologist at
the Caribbean Marine Biological Institute on the island of Curaçao.
But opinions changed as the lionfish took over, he says. “Quite
quickly they were everywhere. They were like cockroaches.”
Since they were first spotted near Fort
Lauderdale, Florida, in 1985, lionfish have colonized more than
4 million square kilometres — throughout the Caribbean Sea,
the Gulf of Mexico and all along the Atlantic coastline of the
southern United States — and show no signs of relenting. Marine
ecologists worry that the invasion will eventually extend to Uruguay,
stopped only by winter water temperatures. It could become one of the
most ecologically harmful fish introductions in the western Atlantic,
says Mark Hixon, a marine ecologist now at the University of Hawaii
at Manoa, and Green’s supervisor at Oregon State. At some sites off
the coast of North Carolina and in the Bahamas, the populations are
5–15 times denser than in the fish’s natural range, sometimes
even reaching 400 fish per hectare.
The conquest
could have profound effects on the biodiversity of coral-reef
ecosystems. Lionfish consume whatever fits in their maws — and a
lot of it. A DNA analysis3 of the stomach contents of 157
lionfish caught in the Mexican Caribbean identified 43 crustacean and
34 fish species, including parrotfish, French grunt and graysby —
important sources of food for local people. Without natural
predators, a lionfish can gobble up 79% of the juvenile fish on a
reef in as little as five weeks.
Divers lay out their haul from a
single-day culling effort intended to drive down lionfish populations
around the Cayman Islands.
The feeding
frenzy could also lead to larger problems. Some of the fish they prey
on clean algae off coral reefs and are already overfished in the
Caribbean. Without these essential species, algae could outcompete
the corals. Simulations by Jesús Ernesto Arias-Gonzàlez at the
Center for Research and Advanced Studies of the National Polytechnic
Institute, in Mérida, Mexico, have shown that a lionfish invasion
would decrease the biomass of corals in a Caribbean reef by about 10%
within ten years4.
Out of control
Green did not set out to study
lionfish. She had just started a doctorate in conservation biology
when she travelled to the Bahamas in 2008 with her adviser Isabelle
Côté, a biologist at Simon Fraser University in Burnaby, Canada. A
student they visited was seeing lionfish all over her study sites.
“Nobody knew anything about them, the basics of where they were, or
what they ate,” says Green.
Green and Côté
wondered whether the native fish would return if they removed the
lionfish. In December 2009, they staked out 24 patches of reef and
arranged for scuba divers to prune the population of lionfish at the
sites every month for 18 months. They predicted that the culling
effort would need to remove 25–92% of the predators, depending on
the site, to keep them from consuming too much of the prey species.
By the end of the experiment, the native fish had rebounded by 50–70%
in the reefs that reached the targeted level of protection5.
Green and Côté were not the only ones
to hunt down lionfish. Earlier that year, the Reef Environmental
Education Foundation (REEF) in Key Largo, Florida, had started
running derbies in the Bahamas to increase local awareness of the
invasion. Green, who had been collaborating with the foundation
during her PhD, got involved in planning the first hunts.
She later decided to use the
competitions to test whether limited hunts could have an impact. With
the help of volunteers outfitted in scuba and snorkels, Green counted
lionfish at 60 sites before and after the derbies in Key Largo and
the Bahamas in 2012 and 2013. On the basis of a preliminary analysis
of the derbies, she says, “there were dramatic drops in the
densities of lionfish in the sites where people fish.” After the
competitions, lionfish densities were slashed by more than 60% over a
100–150 km2 area compared with pre-derby levels. “It’s
like pulling weeds from your garden,” she says. “You’re not
going to completely get rid of them, but below a certain level, they
won’t cause problems.”
Lionfish recolonized the sites within
six months, but the animals were significantly smaller, which helped
to reduce pressure on the reef. Smaller lionfish eat less, prey on
smaller fish and produce fewer young.
Ted Grosholz,
a marine ecologist at the University of California, Davis, says that
the data collected by Green and REEF support the idea that derbies
can effectively control lionfish populations in selected areas. They
also dovetail with results from other lionfish control efforts. When
the fish invaded the Dutch Caribbean in 2009, volunteers immediately
began to use spear guns to remove lionfish from the island of
Bonaire, but did nothing in neighbouring Curaçao. After two years of
spearfishing, Vermeij and his colleagues found that the lionfish
biomass in the treated areas of Bonaire was just one-third of that in
the unfished areas, and about one-quarter of what was seen in
Curaçao6.
On Target
The lionfish contests have been much
more successful than some other efforts that have used hunters to
control invasive species. In 2013, for example, the Florida Fish and
Wildlife Conservation Commission organized the first Python
Challenge, a month-long event with cash prizes that enlisted
professional and amateur hunters to remove Burmese pythons (Python
bivittatus). But the pythons proved tough to catch because they are
hard to spot in the Florida brush; the hunters caught just 68 snakes
from a population that is estimated at 30,000–100,000.
“Quite quickly they were everywhere.
They were like cockroaches.”
Jason
Goldberg, a biologist at the US Fish and Wildlife Service in
Arlington, Virginia, says that derbies could be improved by
incorporating the results of research. Organizers need to calculate
how many individuals to remove, whether it is better to cull older or
larger individuals and how their density affects the health of the
population. That information can then be used to set hunting targets
— and prevent the kinds of problems that arose when Australia
culled red foxes (Vulpes vulpes). The 2002–03 Victorian Fox Bounty
Trial removed one-fifth of the state’s red foxes but ended up
boosting the population because the survivors thrived when they had
less competition for food7.
Cash incentives can help by drawing
amateurs into efforts to control invasives. In the Pacific
northwest,
for example, anglers are offered $4–8 for every northern pike
minnow (Ptychocheilus oregonensis) they capture to deter the fish
from preying on young salmon. The programme has removed more than 3.9
million fish and slashed predation by 40%.
Goldberg says that research on lionfish
derbies should offer insight into how often — and when — they
should take place at each location. He adds that new steps might be
needed, such as encouraging commercial fishing of lionfish to make
the species more common in restaurants.
The lionfish invasion and the success
of the derbies has led to policy changes in Florida. In August,
wildlife regulators relaxed hunting restrictions in the state to
allow divers wearing rebreathers — devices that allow them to
remain in the water for longer — to harvest lionfish. It will also
now allow derby participants to spear lionfish in areas where
spearfishing is otherwise prohibited. “For marine protected areas
to function as conservation areas, it’s important that the biology
and ecology be conserved to the highest level possible, and that now
requires lionfish control,” says Morris.
With her results pointing in a positive
direction, Green intends to continue analysing data from lionfish
derbies, including an event in Key Largo on 13 September. When she
shares her research findings with the divers, it tends to fire them
up, she says. “There’s this good community feeling at the derbies
that this is a tool that can have a positive effect and help to
suppress the invasion.”
(source: NAT.COM)
