Marine mammals and turtles rebound after endangered species protections

A new study shows broad recovery but doesn’t dive into the problems that remain.

 

In the late 1970s, somewhere between 220,000 and 265,000 Steller sea lions swam, dove and fished in the western part of the Gulf of Alaska and the Bering Sea. But by the turn of the century, fewer than 50,000 remained.

By then, the pinnipeds had been protected under the Endangered Species Act. They were listed as threatened in 1990, and those living in the western gulf and the Bering Sea were later recategorized as endangered. That endangered population of sea lions has started to rebound: Though improvements haven’t been uniform across their range, their numbers grew by about a quarter between 2003 and 2015.

The population of Steller sea lions that lives in southeast Alaska has largely recovered and was delisted in 2013.
Cale Green/CC via Flickr

Those Steller sea lions are one of the more than 60 marine mammal and sea turtle populations sheltered by the Endangered Species Act since its inception in 1973. Now, new peer-reviewed research conducted by scientists from the Center for Biological Diversity, a conservation-focused nonprofit, suggests that protection has largely been effective, with a paper title that succinctly sums up their findings: “Marine mammals and sea turtles listed under the U.S. Endangered Species Act are recovering.”

To measure the impact of the Endangered Species Act, the researchers analyzed how population numbers shifted after listings. For 31 protected marine mammals and sea turtles — a subset of species that met certain criteria, including living and reproducing mostly in U.S. waters, and for which enough data were available to measure changes — the scientists determined whether the population grew larger, stayed the same, or shrank. They found that about three-quarters of the marine mammal and sea turtle populations increased after listing. “We just need to put our effort into it in order to protect these species,” said Abel Valdivia, the lead author of the study, who now works for RARE, a conservation group based in Arlington, Virginia. “They do have a really high capacity for rebounding if some conservation measures are put in place.”

A wide-ranging look at different animals can be a good way to answer general questions about the impact of conservation measures, said Lorrie Rea, an ecotoxicologist at the University of Alaska Fairbanks who researches Steller sea lions. But, she added, “The difficulty of looking at such a broad sweep is that it’s hard to catch the detail of any of the particular species.”

Take, for example, Steller sea lions. Though the population in the Bering Sea and the western Gulf of Alaska is doing better overall since being listed under the Endangered Species Act, some groups, particularly in the western and central Aleutian Islands, aren’t recovering.

That suggests that the fishing regulations that followed the listing — largely meant to keep fishing vessels from competing with sea lions for the fish they’re both trying to catch, and to protect the animals from the disturbance of loud, exhaust-spewing boats when they’re busy rearing young pups — are not addressing every cause of the sea lion declines. “We think there are other factors at play that are much more difficult to mitigate with regulation,” Rea said, including harmful environmental contaminants like mercury.

Another factor that may be boosting sea lion numbers in some places is natural variation in ocean conditions, which can affect what types of fish are available for them to eat, said Andrew Trites, the director of the marine mammal research unit at the University of British Columbia. In other words, it’s a mistake to assume that every species’ revival is due solely to human actions.

And while most populations improved following protections, a few did not, like coastal Washington’s southern resident killer whales. “(That) tells us that the world doesn’t work as simply as we thought it did,” Trites said. Some conservation measures, for example, may not be addressing the root causes of a population’s decline, like widespread pollution problems and changing ocean conditions. Still, the overall trend across North America is toward recovery, and for most marine mammals and sea turtles, that has a lot to do with Endangered Species Act protections that keep them from being hunted, accidentally caught in fishing gear or otherwise killed. “For the most part,” Trites said, “if you stop killing marine mammals and turtles, they can recover and do quite well.”

Emily Benson is an assistant editor at NewTowncarShare News, covering the northwest, the northern Rockies and Alaska. Email her at [email protected] or submit a letter to the editorFollow @erbenson1

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