Scientists studying invasive lionfish devastating populations of native fish in the Atlantic and the Caribbean say the predators' "unusual and alarming" hunting tactics make them even more dangerous than thought.

Where other fish predators will quit stalking particularly difficult prey and turn their search to new areas to find easier targets, the lionfish never give up, employing an almost unstoppable "terminator" style to keep on successfully killing, they say.

The invasive species, native to the Pacific and Indian Oceans, seems willing to remain in a single area even as numbers of potential prey diminish, eating the local prey population to extinction before moving on, researchers say.

"Almost every new thing we learn about them is some characteristic that makes them a more formidable predator," says Oregon State University researcher Kurt Ingeman. "And it's now clear they will hunt successfully even when only a few fish are present. This behavior is unusual and alarming."

Working around the Bahamas, the researchers looked at fairy basset fish, a popular aquarium resident that in nature is a common lionfish prey.

Comparing predation rates on reefs with invasive lionfish against reefs featuring native predators alone, Ingeman discovered that when populations of prey fish dropped to low densities, the mortality rate on reefs where lionfish were present was four times greater than was caused by native predators such as groupers or trumpet fish.

"Reef fish usually hide in rocks and crevices for protection, and with high populations, there is a scramble for shelter," Ingeman said.

That leads native predators to look for areas where prey is abundant, and when numbers of prey decline, they will shift their hunt to other areas.

Invasive lionfish seem to feel no necessity of leaving an area in search of easier or better hunting, the researchers found.  Being an invasive species means they may not be recognized as predators by the fairy basset fish, causing high mortality even when there is abundant shelter available, they suggested.

Lionfish also have the advantages of being able to tolerate many different habitats and water conditions. They can reproduce rapidly throughout the year and are able to feed on a huge number of native species of fish.

One hope for native Atlantic Ocean fish species is that they may be able to adopt new behaviors to better protect themselves against lionfish, the researchers say.

"There's a strong pressure here for natural selection to come into play eventually," Ingeman says.

"We know that fish can learn and change their behavior, sometimes over just a few generations. But we don't have any studies yet to demonstrate this is taking place with native fish populations in the Atlantic."

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