Sea Lion Decline: 'Autopsies From Space' Starts Pointing Fingers

For decades, experts have known that the Stellar sea lion (Eumetopias jubatus) has been facing major and startling declines in population. However, unlike with most major predator species, what is driving these animals' decline remains a mystery. Now data from an ongoing investigation has come in, and it reveals some startling findings.

According to the NOAA Fisheries and the Ecological Society of America (ESA), Stellar sea lions as a whole are only threatened at worst, when it comes to overall prevalence, and maintain healthy and potentially increasing populations along the coasts of southeast Alaska, British Columbia, California, and Oregon.

However, things are not looking so good for sea lion groups in the western distinct population segment (W-DPS), consisting of the central and western Gulf of Alaska, the Aleutian Islands, and the coasts of Japan and Russia.

In fact, according to the NOAA, the ESA, and even the IUCN Red List, W-DPS Stellar sea lions have seen a whopping 80 percent decline in the last three decades, first being labeled as "threatened" and then "severely endangered."

Strangely, only rarely did experts ever see a W-DPS Stellar's corpse, and what few samples were ever examined showed a healthy animal which died of natural or expected causes. Of course, as the IUCN reports, the animals have always been threatened by hunting and disease, but the NOAA and ESA even saw to enact fishing restrictions in some Alaskan waters to ensure that the sea lions had enough to eat; starvation, of course, being a suspected cause of this inexplicable decline.

However, new data 10 years in the making has offered a way to observe and record these sea lion deaths, and is indicating that predators may be playing their part.

Markus Horning, an expert of wildlife ecology at Oregon State University, recently wrote in The Conversation how he and his colleagues surgically implanted small electric transmitters into the bellies of Stellar sea lions living in the W-DPS in the hopes of learning more about how and why these animals are disappearing.

"Don't worry, we checked that [the implant] does not alter the behavior or survival of the animals," he reassured readers. "After all, we don't want to influence the data we need!" (Scroll to read on...)

According to Horning, these tags eventually float to the surface after their host dies, freed by decomposition, dismemberment, or out the backside of a larger predator.

"No matter where these sea lions go, we eventually get a sad email that confirms one of our study animals has died," he added. "Since tag data is relayed by satellites, we call these 'autopsies from space.'"

Since the project began in 2005, 17 of these tags have sent their morbid emails out, with two tags boasting insufficient data. The remaining "good" data has shown that 15 sea lions died of something perfectly natural: predation.

"We could only guess who might have done this: killer whales, white sharks, salmon sharks and maybe sleeper sharks have all been reported as predators of sea lions," said Horning.

However, he added that that last predator, the Pacific's little-understood, cold blooded, and incredibly patient sleeper shark, looks to be a prime suspect.

That's because some of the most recently recovered tags claim to have spent days upon days in a dark, airless, and cold environment before suddenly finding sweet freedom and returning to the ocean surface. Even the stomachs of aggressive surface sharks are warmer than the chilly deep sea, so Horning and his team found themselves only with sleeper sharks to blame.

And while that doesn't sound like particularly important news, the expert is quick to point out that the sluggish sleeper shark was once a common bycatch in local fisheries. With fishing restrictions put into place in the W-DPS, they may only exacerbate the problem, as more sharks will be left to prey on the vulnerable Stellar sea lion population.

Horning adds that he hopes the "autopsy from space" revelation might affect future fisheries management decisions, even if it didn't exactly get to the bottom of the disappearing sea lion mystery.

You can learn more about the investigation and its implications by watching a recent presentation from Horning here.

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