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Study: Otters Help Combat Global Warming

By | September 12, 2012

Sea otters rest in waters near Sitka. A new study says otters help kelp growth, which reduces carbon dioxide, which causes climate change. Photo by Ed Schoenfeld, CoastAlaska - Juneau

A new study is adding another dimension to the sea otter debate. The research shows the marine mammals help reduce carbon dioxide in the atmosphere, a major contributor to climate change.

Jim Estes remembers taking a look around the bottom of Sitka Sound about 20 years ago.

“When we were diving in that area back in the early 1990s, the sea floor was just covered with urchins and there was virtually no kelp,” Estes says.

“Two years ago, when we went back and looked at the same sites, there was not an urchin to be found and there was kelp everywhere.”

Estes is a professor of Ecology and Evolutionary Biology at the University of California campus in Santa Cruz.

His latest research takes a look at kelp forests, and how much carbon dioxide they absorb. The otter connection comes because they eat sea urchins, which in turn eat kelp.

Working with existing data and other researchers, Estes took a look at coastal waters with no sea otters and those with a full population.

“The effects of sea otters in that system on carbon dioxide concentrations would be significant. And by significant, I mean whether or not you have otters in the system would account for roughly, approximately 10 percent of the total carbon. That’s a lot,” he says.

And by cutting carbon dioxide, otters also reduce ocean acidification, which results from CO2 dissolving in water.

“That’s a whole other area of work that we and others have been looking at. And if, for example, you look at pH, which is a measure of acidification, and you measure it inside a kelp forest and then a couple hundred yards away, it’s always higher within the kelp forest, which means the acidification level is lower,” he says.

He says the CO2 changes would be in affected coastal areas, not worldwide.

Otter populations are booming in Southeast Alaska. And that’s brought a lot of attention from fishermen, economic analysts and biologists.

“I heard about this research a couple years ago when [preliminary] findings were presented at a scientific conference. And we do work with one of the authors of the study,” says Verena Gill, the U.S. Fish and Wildlife Service biologist who headed up Southeast population studies.

That research shows 12 percent annual growth in the southern part of the region, and 4 percent in the north. Other coastal areas, such as Kachemak Bay near Homer, have seen even larger increases.

She says the new report is good research.

“I just think it adds another piece to the puzzle of the many jobs that sea otters do in a healthy marine ecosystem,” Gill says.

The new study focuses on waters from southern British Columbia to the end of the Aleutian Islands. Southeast and most other areas lost their populations to Russian and American hunters about a century ago. Otters were reintroduced to the outer coast almost 50 years ago.

In an earlier interview, Phil Doherty of the Southeast Alaska Dive Fisheries Association said their rapid spread and voracious appetite hits his members hard.

“The areas that are most affected are the areas that have the largest food source. And those are the species that we harvest … sea urchins, sea cucumbers and geoduck clams,” Doherty says.

Sea otters are a protected species and only Alaska Natives can hunt them. There are also strict limits on how their pelts can be sold. Some commercial fishermen and Native groups have called for measures allowing more to be harvested.

Otter supporters have fought for continued protection in part because kelp forests offer shelter that boosts salmon, herring and rockfish populations.

The new research adds to those arguments. But Estes doesn’t want to exaggerate impacts on the planet’s overall carbon dioxide level.

“It’s going to be pretty small. We haven’t made that calculation, but this is just a teeny little part of the world. So I don’t think the story really is relevant on a global scale. It’s just demonstrates a process on a local scale,” Estes says.

Ester co-authored the study with Chris Wilmers, another U.C. Santa Cruz professor, as well as researchers from other schools, including the University of Alaska Fairbanks.

The study first appeared in the publication Frontiers in Ecology and the Environment.

Earlier reports:

Feds try to clarify rules on use of sea otter

Central Council addresses Southeast sea otter issue

Otter measure drops whole-pelt sales provision

Report says sea otters hitting dive fisheries hard

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