Eradication of the invasive lionfish is no longer possible in Bermuda waters, with steps now being taken to ensure their numbers are curtailed, the environment ministry has said.

A spokeswoman for the Ministry of Public Works and Environment said that while numbers of lionfish, which pose a threat to our native fish populations, have stabilised thanks to culling efforts by divers in the shallower depths, there remained work to do on managing the fish in deep water.

In 2019, the Government teamed for a research paper with local company Atlantic Lionshare which has been working on The Reefsweeper — a remote-controlled mini-submarine designed to hunt lionfish in deep water.

The spokeswoman said there were further measures being considered to create marine protection zones for local fish.

She said: “[At present] continuous culling by trained divers remains the most effective control method.

“Research into new technologies such as remotely operated vehicles for deepwater removals is under way, and measures to strengthen marine ecosystems and boost native fish populations that compete with lionfish, such as additional marine protected areas, are being considered.

“It is important to note that eradication is no longer possible. Lionfish now occupy the entire western Atlantic, from shallow waters to depths of 1,000ft, and their drifting egg sacs allow them to spread widely.”

Jaché Adams, the Minister of Public Works and Environment, said: “Like other jurisdictions in the region, Bermuda will need to continue long-term management and lionfish control programmes to reduce their impact on our native fish and invertebrate species and our marine ecosystems.”

Lionfish are native to the Indo-Pacific and may have made their way into Bermuda’s waters after escaping into the ocean from home aquariums.

The invasive species began to be detected here from about 2001.

While numbers initially remained low, their population began to surge between 2012 and 2015.

With no known predators in Bermuda the highly reproductive fish, which come with a voracious appetite, pose a threat to domestic fish populations by competing for the same food or targeting them as prey.

According to the Lionfish Taskforce, which collects catch and sighting data, 2,634 lionfish were caught or sighted locally last year and so far this year there have been 1,211.

Only about 6 per cent are sightings alone, the spokeswoman said.

She said: “At the time, [when lionfish numbers began to increase], new research improved our understanding of lionfish behaviour, particularly that dawn and dusk were the most effective times to target them, and the introduction of tournaments and a vendor programme encouraged regular removals, which increased catch rates.

“While culling has not eliminated lionfish, it has helped slow their population growth and keep numbers lower than they would otherwise be.

“Local studies show that lionfish expanded steadily from 2015 to 2019, but their numbers now appear relatively stable.

“Importantly, they are not as dominant on Bermuda’s reefs as in other parts of the Atlantic, likely due to culling efforts and the presence of relatively stable populations of native predators such as coney and red hind, which compete with lionfish for food and shelter.”

Lionfish have a broad diet which includes juvenile fish, shrimp and other invertebrates, but the spokeswoman said Bermuda has been “somewhat fortunate”.

She explained that lionfish here tend to favour deeper waters during the summer months when juveniles are most vulnerable in shallow water nursery areas.

Bermuda’s native mid-sized predators also appear to be producing enough offspring that the loss of some juveniles is not critically damaging to their populations.

She added: “Local scientific surveys have not shown significant differences in the abundance of juvenile fish at sites with lionfish compared with those without, and this is likely because lionfish do not generally cluster in large numbers around Bermuda, except in a few deep water hotspots where food sources are unusually plentiful.”

Atlantic Lionshare said in 2019 that surveys conducted three years earlier around the edge of Bermuda by the Nekton Mission showed lionfish present at depths as great as 300 metres.

A spokesman for the company said at that time: “There is an urgent need to harvest lionfish at depths beyond the limits of humans using dive gear.”

The Department of Environment and Natural Resources and the Bermuda Institute of Ocean Sciences tested lionfish traps in deeper waters, but the move came with the risk of by-catch.

The Reefsweeper was accordingly designed to be able to target the species.