Luiz Rocha, the curator of ichthyology at the California Academy of Sciences, writes from Belize, where he conducts research on the social wrasse, one of the world?s most endangered fish.
Saturday, Dec. 22
Despite the occasional swollen, painful sting, we have had little problem putting our hands on the invasive lionfish here in Belize. During our last day of diving we collected another 17. We would have collected many more if we had additional divers.
They are everywhere, and in much greater numbers than their native range in the tropical waters of the Indo-Pacific. We think that two factors are influencing their numbers in the Caribbean: they are released from competition and the Caribbean prey is ?na?ve.?
They are not the first invasive species to encounter a lack of natural predators and competition combined with easy prey. A similar pattern was observed in the brown tree snake, which was accidentally introduced to the island of Guam shortly after World War II. The invader found a forest free of predators, and stocked with plenty of unwitting prey (native forest vertebrate species). They reached such high numbers that many native species were driven to near extinction. They also tended to climb utility poles, shorting circuits and causing power outages.
In its natural range, the brown tree snake was never able to dominate so completely. There, young snakes faced a shortage of juvenile lizards, their primary food source.
Diversity plays a natural role in controlling lionfish numbers?in its native habitat. Sometimes four different lionfish species coexist in a single dive area.?These species have similar diets, so they compete for the same resources with one another, and also with other ambush predators.?And some of these ambush predators, like large groupers and sharks, eat lionfish in their native range. But these threats are absent in the Caribbean.?There, the Red Lionfish (Pterois volitans) dominates, and has few competitors and would-be attackers.
Also, like the bird with no natural fear of the brown tree snake, the social wrasse seems unaware of the threat a lionfish poses ? often straying dangerously close to them.
Our last morning in the field was dedicated to carefully preserving and packing the stomach contents of 51 lionfish ? the partially digested bounty of our trip. Among those contents, we found at least 20 critically endangered social wrasses. That number makes the social wrasse the most common prey item found inside lionfish in the area.
As I prepare to leave the Carrie Bow Key field station, my mind turns to the question of what to do about this invasion in progress. And a lot of readers asked about potential solutions. One might be gastronomical.
These are tasty fish. Since we only needed their stomachs for the research, we also carried out a little experiment for the palate: we had lionfish ceviche, fried lionfish and lionfish sashimi with a bit of soy sauce and wasabi. It was simply delicious in every preparation. The consistency of the meat is excellent, especially for sashimi, and its very mild taste reminds me of pricey red snapper and rockfish.
A large-scale commercial catch would potentially mitigate population growth. But there are complications. First, these fish are small, and economic viability would require catching them in high numbers. This might seem like a good thing, given that the objective is to keep their numbers down. But their poisonous spines make these fish very hard to handle even when they are being cleaned. (I?ve got some first hand experience with that issue.)
Capturing them also poses another problem. While they are extremely easy to catch with a spear, they only eat live fish. So hook and line will not work. You?ve got to get in the water, up close and personal. But even with all of those limitations, demand will certainly move things the right way, so I encourage everyone to ask for lionfish in Caribbean sea food restaurants.
Some readers also mentioned the practice of feeding them to groupers and sharks. While this seems like a nice option at first, the groupers and sharks in many areas are learning to seek divers for a free food handout rather than acquiring a taste for the lionfish. Most locations of the Caribbean are so overfished that it is hard to find large fish to offer dead lionfish to in the first place.
One reader made another very important point. This invasion likely started with an aquarium release, and the lionfish is not the only invasive aquarium fish present in tropical waters. There are dozens more, including tropical Indo-Pacific angelfish, butterflyfish and surgeonfish. I know aquarium owners do get attached to their fish. They might think that the most humane thing to do when a fish grows too large for its tank is to release it in the nearest large body of water. But doing that will only contribute to the invasive species problem. So here is my suggestion if you have an aquarium fish that is becoming a problem for any reason, just take it back to the aquarium store where you bought it. Store owners will gladly take the fish back most of the time as they can try to resell it to someone with a larger tank.
Regardless of what we do, one thing is certain: the lionfish (as is the case with many other invasive species) is here to stay. They have such a broad habitat and depth range that specialists now agree that it is impossible to eradicate them. All we can do is try to control their numbers. We are confident that the ecosystem in Belize will adjust and nature will find a way. The better question is: how long will this take and just how much will the Caribbean fauna?particularly, the social wrasse?suffer while it does?
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