A black group eel lurking in the Pacific Ocean seemingly couldn’t be stopped. A new study suggests it had a short lifespan. The eel was seen as long as 8 meters (26 feet) – and like many other large-bodied fish, a week or two.
But it got lonely after a few days. The fish died, and found itself trapped in the frigid waters about 250 miles east of Hawaii.
“For this type of fish, life on the edge for several days, with time to decay, and topographic stressors are all stressors that can lead to failures,” said Jesse Higgins, a scientist at Conservation International, who co-wrote the new study along with David Frank at the University of California, Davis.
Higgins, Frank and colleagues put 528 live specimens of the black group eel under the microscope in the hopes of determining why the fish failed, and what eventually killed it. The study, published Friday in Scientific Reports, laid out the fish’s distress to make sure they’d stay within the bounds of acceptable publication.
But what really concerns Higgins is the bigger picture of where these common-to-the-Pacific species go if they die.
“It’s a great thing for us to know how many of these species are out there, but the mystery isn’t about how many species are there but how many are out there and what the health of those species are,” he said. “A catastrophic failure is a story all by itself, but we don’t have any good ways to know that.”
Over the last decade, research has found dramatic declines in other species like black group eels, but that doesn’t mean they don’t live far enough offshore to be seen, Higgins said. Instead, it’s the conditions we have that are the real problem.
Humans have turned most of the open ocean into a home for big tuna and marlin. The black group eel usually needs deep, colder waters for its sort of escapement, the process by which an adult lives for a week or two at least until it can burrow down a reef. It’s unlikely this species would survive deep off the coasts of Washington or Alaska, he said.
“The closer we get to (that) scale, the more likely it is that we’re not going to have a functioning mortality system for these fisheries,” Higgins said.
Right now there is no way to work out a survival rate. But scientists hope to put together a better picture with next-generation undersea robots that allow detailed and real-time tracking of the environment.
Even if the black group eel does live, we can probably count it out for this predator-fishery as well. Higgins said there is an evolution argument for why black group eels simply aren’t big enough. A fish with a body size comparable to a black eel would need an ocean more than 300 kilometers long, or nearly twice as deep, to survive. They’d be able to hunt in that habitat and mostly fend off larger competitors, but after a couple weeks, they’d be too short for this remote ecosystem.
“We can see it’s driven by evolution, we’re just not going to see it on the screen,” Higgins said.