SEATTLE — Federal biologists plan next month to attach tiny satellite devices on Puget Sound’s endangered orcas off the West Coast to better understand where they go during winter. But some whale experts worry the tags — about the size of a 9-volt battery with two darts — could injure the orcas.

While dart tags have been used on other whale species, this is the first time they would be used on the southern resident killer whales that frequent the inland waters of Washington state and British Columbia.

Brad Hanson, a wildlife biologist with the National Oceanic and Atmospheric Administration Fisheries Service in Seattle, and his colleagues received federal approval last month to implant the transmitters on the dorsal fins of up to six orcas.

The orcas spend summer months in Puget Sound, but “that’s only half the story,” Hanson said, adding “we don’t know where they spend the bulk of their time.”

Tracking the animals in the winter would pinpoint their range of travel and help inform their critical habitat, he said. Visual sightings and ship surveys have shown the animals travel as far south as Monterey, Calif., and as far as the north coast of British Columbia during winter, but the information isn’t sufficient, Hanson said.

Ken Balcomb, senior scientist with the Center for Whale Research in Friday Harbor, Wash., said the dart tags are too invasive.

“I don’t believe the injury to the animals is warranted,” said Balcomb, who keeps a running census of the orcas. “It’s an injurious process. It sticks barbs in the whales that are serious attachment devices that do cause injury and can potentially become infected.”

Balcomb had applied for a federal permit in 2008 to tag the Puget Sound orcas because he believed at the time the devices were not harmful. He received federal approval in 2009, but he later declined to tag any orcas after witnessing injuries and wounds to other tagged whales.

“If you take the diameter of a golf ball, that’s the spread of tissue damage from each of two barbs. These will heal over time if they don’t get infected. Some of the barbs don’t come out,” Balcomb said.

The whale’s tissue will be impacted but will heal, Hanson said. “Within a few weeks, it basically heals back up, so you’re left with a couple of marks,” he added. They’re within the range of scars and marks that whales encounter naturally.

Hanson proposes tagging up to six orcas — adult males or non-reproducing females. He has been tagging 15 species of whales, such as humpbacks and blue whales, under a five-year federal permit. Puget Sound orcas were added to more recently.

Dr. Pete Schroeder, a veterinarian who has studied marine mammals for decades, said he doesn’t believe tags are harmful. It would be like a pinprick to such a multi-ton animal, and “it would have no lasting effect,” he said. “Any time the skin is broken, there’s a route for infection. That doesn’t negate the animal’s ability to fight infection,” Schroeder said.

Hanson will go out on a research boat for three weeks in February to try to find the whales off the Pacific Northwest coast, a task not without challenges, he said.

Researchers will use a cross bow or an air gun to shoot the dart tags, which have two barbs about 6 centimeters long. The tags provide information for between 16 and 94 days and usually fall off as the whales swim, Hanson said.

Balcomb and other orca advocates questioned whether the benefits were worth harming the orcas, whose population now stands at 89.

“What are we going to do with the information?” he asked. “Are we going to designate habitat if we get more information?”

In its comment letter to NOAA on tagging orcas, officials at The Whale Museum on Friday Harbor advocated more passive measures to track the whales, such as listening to their distinctive sounds. They said NOAA has spent thousands of dollars on surveys that found the whales in shallow waters of the West Coast, but little has been done to protect them from naval warfare training in the area.

“Therefore, we cannot see a compelling need to use an invasive technique to show similar data trends when the existing data observations were not used, or were not adequate, to take conservation measures that would have prevented potential impact to whales in areas and times of the year when they have been demonstrated to use the area,” they wrote.

“You’re dealing with an endangered species, so you really should look at the less invasive ways first,” said Fred Felleman, an environmental consultant who is on the museum’s board.