The Invasion of the Lionfish – 2016 update
The first report of a lionfish in the northern Gulf of Mexico was in 2010. It was a small individual that struck more curiosity than anything else. By the end of the following week another was seen and now, here off the coast of Pensacola, are some of the highest densities found anywhere in the south Atlantic region. The massive expansion of lionfish in the Pensacola-Mobile area generated much concern with fishermen, divers, and local officials. State and local agencies, as well as nonprofits which formed after workshops on this issue, have been working on managing this invasion.
THE NATURAL HISTORY OF LIONFISH
There are actually 9 species of what are called lionfish. They are members of the Family Scorpaenidae, which include six species of native scorpionfish. The lionfish differ from local scorpionfish in having much longer dorsal and pectoral spines and rays. They also have a vertical striping pattern across their body which includes their head and fins – they are actually very beautiful. Of the 9 known species only 2 are believed to be in the Atlantic and Gulf. The Red Lionfish (Pterois volitans) is from the western and central Pacific, including the western coast of Australia. The Devil Fish (Pterois miles) is from the Red Sea and Indian Ocean. Visually separating the two locally is very difficult. Within their native range the Red Lionfish has 1 additional dorsal and anal fin ray; but where the two species overlap within their range identification requires genetic testing. DNA work suggests that over 90% of the lionfish in the south Atlantic region are the Red Lionfish. However, the appearance and natural history between the two species is very similar; so we treat them as “lionfish”.
In the Philippines a study found lionfish to be more common on reef associated habitat (sand patches, reef channels, and artificial reefs) rather than on the large coral reefs themselves. In Guam, which had fewer lionfish than the Philippines, they were more common in turbid water areas – such as river mouths and channels – when compared to large coral reefs. In the south Atlantic region several studies have looked at habitat preference. Here lionfish prefer aggregate reefs to patch reefs. They prefer hard coral structures over soft corals and structures that provide overhangs. Whether the reef is in a healthy state or not does not seem to matter. One local study found they do prefer artificial reefs to natural hard bottom. There are a couple of studies that have found lionfish in seagrass beds and mangroves. Most of these are smaller fish and suggest that they may begin life, as so many of native fish do, in these estuarine habitats and then move to nearshore reefs. Some studies support the argument that larger lionfish then move further offshore to deeper reefs; but not all studies agree with this scenario. In the Pensacola area, lionfish have been found mostly on artificial reefs beginning around 30 feet of depth, and increase in number and size as the water depth increases. Captures and sightings on inshore reefs and grass beds have been recorded, but are rare. Most studies suggest strong site fidelity; they do not move much from the reef they have claimed.
Their native range includes the Red Sea, Indian Ocean, and western and central Pacific. In the south Atlantic region, they are found across the south Atlantic as far north as North Carolina and east to Bermuda; there are few reports further north. They have invaded the entire Caribbean and Gulf of Mexico. Barriers to their continued dispersal are not fully understood. They do not seem to be impeded by estuarine water; one study has shown they can survive in water as low at 7‰. However, temperature may be a barrier. Thermal low tolerance has been found to be 10°C (50°F) and the fish stop eating at 16°C (61°F). These temperatures can be found across the continental shelf but may limit their distribution north and at depth.
Growth and Reproduction
Female lionfish become sexually mature at 180mm in length (7 inches), and this generally occurs within the first year. Lionfish have a complex courtship behavior that typically begins late in the afternoon and into the evening. Once courtship has been completed the female will ascend from the reef and release two egg masses covered in a gelatinous sac. The egg masses are buoyant and float in the ocean currents, contributing to their dispersal across a large area. Dissections of mature females indicate they are able to produce year round, and typically release between 25,000 and 30,000 eggs every 4 days; this equates to about 2 million eggs / female / year. This egg mass generally drifts for 26 days at which time the hatchlings (1.5mm or .06 inches) settle out. The time of hatching is temperature dependent and will occur at different rates regionally. Again, some studies suggest that young settle in shallower waters and move to deeper reefs over time, showing strong site fidelity.
Lionfish are venomous. The venom is produced by a spongy tissue located along the base of some dorsal and ventral spines; the first 13 dorsal spines – the first one each pelvic fin, and the first 3 of the anal. This spongy tissue is covered by sheath of skin. When the sheath is disturbed, the tissue ruptures and sends the venom along a groove on the exterior of the spine into the victim. The venom contains acetylcholine and a neurotoxin which is strong enough to ward off most predators. For humans it is quite painful but there are no cases of death. In one report, 117 hospital patients in Martinique (from 2011 to 2014) were surveyed. All of them reported marked pain and local edema. Paresthesia occurred in 90%, abdominal cramps in 62%, and in rare cases surgery was required to deal with other symptoms; most of the patients were male adults. This study found that if the wound was submerged in hot water within 3 hours, there was a significant reduction in pain. People should avoid contact with the dorsal and ventral spines of this fish.
Predator – Prey
There is little known about the predator-prey behavior of lionfish in their native range. We do know locally that they are ambush hunters and voracious eaters. The smaller lionfish seem to prefer invertebrates while the adults prefer fish. One DNA barcode study identified fish species from 5 different orders, 14 families, 22 genera, and 34 species. The most common were gobies and cardinal fish and there is evidence that they may be cannibalistic. There were 45 crustacean markers but the exact identification is unknown. There are few natural predators – probably due to the venom they possess. Their stomachs can expand 30 times the original size, which allows them to literally gorge on reef fish and then fast for long periods. Predation has been found by members of the grouper family but these fish do not prey on lionfish frequently. It is not quite understood what controls their population numbers. Local experiments and sightings suggest that grouper, sharks, and maybe triggerfish prey on them.
INTRODUCTION TO THE UNITED STATES
Initially several methods of introduction were considered but it is now believed that the cause was the aquarium trade. There is little genetic diversity within the lionfish captured over the region suggesting a small localized release. Earliest records of lionfish in the region were from 1987, suggesting the release was from southeast Florida. Whether the release was intentional or not is not known. Following the Gulf Stream, the dispersing egg masses moved north to the Carolinas, east to Bermuda, south to the Caribbean, and have now entered the Gulf of Mexico. The movement in the Gulf was along the southwest coast of Florida north to the panhandle, over to Texas, and south to Mexico. It is one of the most rapid invasions of a marine fish ever recorded.
WHY IS IT CONSIDERED INVASIVE?
The term invasive means different things to different people – but most consider it bad. Here we will define an invasive species as a non-native creature that is causing environmental or economic problems – possibly both. So what about the presence of lionfish is a problem?
Well, one of the first indicators is its rapid expansion – this is an indicator of an invasive problem. One study initially found lionfish in the Atlantic at densities of 21 fish / hectare in 2007. By 2008 those same locations had between 150-350 lionfish/hectare. On many studied reefs, lionfish are the most common predators, displacing native species. One study from the northern Gulf found the presence of lionfish forced red snapper to move farther away from reefs and over open sand. Their voracious appetite can (and has) reduced the forage fish on the reefs. Many of these forage fish consume algae that would otherwise overgrow the coral themselves. The heavy fishing pressure on snapper and grouper leave open areas for lionfish to colonize. This rapid colonization can hinder any efforts to restock grouper and snapper on those reefs. This invasion is can alter the entire reef community.
SO WHAT CAN BE DONE – A MANAGEMENT PLAN
There does not appear, at the moment, to be an attempt by local predators (grouper, etc.) to prey on these fish and thus control their populations. Therefore, most management plans call for human intervention. There are different opinions as to how many should be removed but the range is from 25% of the population/month to 75% of the population / year. Not knowing the population makes effective management more difficult. Though there are reports of lionfish biting hook and line, occurrences are rare and it appears that standard fishing tournaments will not be affective at this time. The most effective at the moment is spearing or capturing via a hand net using SCUBA. Since the onset of the lionfish invasion, spear fishing tournaments either targeting lionfish, or including them as a category, have removed as much as 75% of the known local population. These have been very effective however they are localized and infrequent. Drifting egg masses can replace these populations between tournaments and will need other management practices in order to stabilize the lionfish populations in the region. Divers are more interested in removing lionfish if there is an incentive to do so. Currently the Florida Fish and Wildlife Conservation Commission offers several incentive programs as well as the annual LIONFISH REMOVAL AND AWARENESS DAY. At this event, held the weekend after Mother’s Day, the public is made aware of the issue and a tournament is held to remove them across the state. In 2016, 8089 lionfish were removed during the event in Pensacola.
Developing the fish as a commercial seafood product is also being explored. In Florida, diver/harvesters are required to have a salt water products license in order to sell their catch. There is no season or bag limit – though removing within national and state parks, as well as marine preserves is illegal without permission. There are currently several wholesale and retail seafood markets who are certified to purchase from local divers. The issue, at the moment, for this management practice is price and the number of certified harvesters to collect. Lionfish is currently quite expensive to harvest and many local restaurants are not willing to pay the high prices. However, there are markets outside of Florida who are willing to pay – and they are. The development of a lionfish trap would reduce the cost of harvesting the fish and thus make more available in local markets. Several federal and state agencies are currently funding trap experiments.
Finally, there is the idea of marketing the removal of lionfish as a tourist adventure. “Lionfish Trips” are being offered in several locations within the state.
It does appear that the lionfish will be here to stay. However, to avoid potential harmful impacts to our reef ecosystems, a good management plan will need to be enacted. Such plans have been developed on the local, state, and federal levels.
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