Do otters eat a lot of rockfish?

Here’s some irony. Rebounding rockfish populations have created a concern that river otters may be eating enough to hamper continuing population growth.

“It’s more of a lack of information,” said Joe Gaydos, director and chief scientist of SeaDoc Society. Predation on rockfish populations is poorly understood. “It’s better to take a look at the issue.”

Banning commercial fishing for rockfish on the U.S. side of the Salish Sea and creation of several marine protected areas probably have been effective in boosting the number of rockfish.

But then there are those hungry otters.

“River otters are not true marine mammals,” Gaydos said. Although they can fish in the ocean, “they can’t go so far out from shore that they can’t get back for a drink of fresh water.”

“They look exactly like otters in rivers in Montana or Illinois. They are very different than sea otters, which are true marine mammals,” he said.

While river otters spend time on land, their hydrodynamic body layout is well-adapted to swimming and hunting for food. They have a long, powerful and flexible tail and webbed feet designed for speed and efficiency.

Fortunately for our endangered rockfish, though, these members of the weasel family seem to specialize in the small lower intertidal and shallow subtidal fish such as the gunnels, sculpins and pricklebacks.

SeaDoc funded research in the San Juan Islands that was published this year in Aquatic Mammals Journal. Researchers visited otter latrines around the San Juan Islands. Otter scat was examined for fish bones and otoliths (ear bones) to determine species and age of prey.

Otters are indeed seafood fanatics: fish were present in 100 percent of the samples, and provide the majority of an otter’s diet. Most of the fish were not rockfish, however, and only up to 22 percent of any scat had rockfish bones.

Researchers found that rockfish occurred most frequently in samples from San Juan Island (22 percent), and most rarely (2.7 percent) from Fidalgo Island. Also encouraging was that otoliths showed that less than half the rockfish taken by otters were adults, the breeders that are critical to replenishing rockfish stocks.

There will be additional research because there is still a concern that rockfish populations will be easier targets for river otters (and other predators) who are attracted to an increasing food source.

After all, Gaydos said, “If you don’t look, you don’t know.”

Join the flock: Oct. 18 is Birds at the Burke day at the Burke Museum of Natural History and Culture in Seattle.

All-day activities include examining hundreds of bird specimens, including delicate eggs with their nests; making a birdfeeder, joining an indoor bird-watching experience, learning how to be involved with Citizen Science projects, and watching as birds are prepared for research.

Live bird shows will be at 10:30 a.m., 12:30 p.m., and 2:30 p.m. Photographer and author Paul Bannick will talk about owls and woodpeckers at 11:30 a.m. and 1:30 p.m. For more information, go to www.burkemuseum.org or call 206-543-5590.

Wildlife to-do list: The state Fish and Wildlife agency offers ideas for your helping backyard wildlife as you’re preparing for the first cold snap:

Leave some “dead heads” on flowering plants to provide seeds for birds and other animals.

If you must rake leaves off grass lawns, just pile them under some shrubs, bushes or other nooks and crannies to provide homes for insects that birds love to eat.

Leave a portion of your lawn unmowed in which small animals can hide or forage.

Save just a little of that dead bramble thicket. It’s a great winter cover.

Fall is a good time to plant shrubs, so replace invasive, exotic Himalayan and cutleaf blackberries with native plants of higher wildlife value such as blackcap (native black raspberry) or red raspberry; native currants or gooseberries found in your area; or native roses such as Nootka or baldhip.

Columnist Sharon Wootton can be reached at 360-468-3964 or www.songandword.com.