EVERETT — Whale watchers and tour-boat operators are concerned about the effect the latest round of sonar testing at Naval Station Everett could have on marine mammals.

A loud “pinging” sound has been heard on board several different boats in the area, including the Mukilteo-Clinton ferry, over the past week and a half.

The sound was so loud that Carl Williams, a tour captain for Island Adventures, heard it on the third deck of his boat moored in Everett near Anthony’s restaurant.

“You can hear it while you’re walking on the dock,” he said.

It’s coming at a bad time, say Williams and others who keep an eye on marine mammals. It’s the beginning of the migratory season for gray whales, several of which venture into Possession Sound and Port Susan to feed on their way north.

At least one whale has been spotted in the area over the past week.

“It’s disturbing, it’s very disturbing,” said Susan Berta, co-founder of the Orca Network in Greenbank.

The testing was first heard Feb. 29 and has been heard several times since. It originated on the USS Shoup, a destroyer stationed at Naval Station Everett, said Sheila Murray, a spokeswoman for the Northwest region of the U.S. Navy.

The testing has been done on and off for years but is relatively infrequent and only takes place with special permission of the Pacific fleet commander in Hawaii, she said.

“The Navy’s been doing this type of activity as long as Navy ships have been in Puget Sound,” Murray said.

The Shoup was at the center of a sonar controversy in 2003. The ship was testing its mid-range sonar in Haro Strait between Vancouver Island and San Juan Island. At least 11 porpoises stranded themselves and died on a nearby beach at the time. A pod of killer whales also was seen “speed swimming” away from the ship, said Shane Aggergaard, owner of Island Adventures, which runs tour boats out of Anacortes and Everett.

Reports by the Navy and National Marine Fisheries Service were inconclusive on whether the sonar was connected to the porpoise deaths.

Passengers and crew on the Mukilteo-Clinton ferry heard the pinging for about an hour Feb. 29, ferry spokeswoman Marta Coursey said.

Williams said he first heard the sound on his tour boat on Feb. 29 and two more times, the most recent being Wednesday. It continued for about three hours in the afternoon each time, he said.

“The first day it was louder and shorter, the second day not as loud but longer,” he said. On Wednesday, “it was not as loud but continuous.”

Howard Garrett of the Orca Network said he heard the sound onboard a boat with others in Possession Sound on Wednesday. The group put a hydrophone — a device used for listening to sounds from underwater — into the sound and connected it to a microphone.

“It still hurts my ears,” Garrett said the next day, adding that the volume was turned all the way down. “They slowly ramped up and lengthened the duration” of the pings over about three hours, roughly from 2 to 5 p.m., he said.

The group also saw at least one gray whale — he’s not sure if it was the same one seen twice or two separate whales, Garrett said.

At first, the sonar showed no apparent effect on the whale, which seemed to be feeding in the water near Tulalip Bay, he said. When the sonar grew louder after about 20 minutes, though, the whale turned and swam north toward Port Susan, Garrett said.

There’s a group of gray whales that visits Possession Sound and Port Susan on their migratory trip every year, whale watchers say.

Normally about a dozen stop over, said John Calambokidis of Olympia-based Cascadia Research. About six of them are the same whales every year and about six are different, as identified by photos, he said. A trio of regulars has been spotted so far this year, Calambokidis said.

He said that gray whales hear at a lower frequency than dolphins, porpoises and orcas, so the mid-range sonar of the Shoup might not affect them as much, he said.

“I don’t think we know what effect it might have in this circumstance,” he said.

Aggergaard said he understands the Navy’s need to test the sonar but said it shouldn’t be done during migratory whale season, which runs March through May.

“This group of gray whales that come in there are pretty unique, and we’re pretty protective of them,” he said.

Williams, the boat captain, said it could spook the whales from making future visits.

“The repercussion could be next year, we might not see them come back next year,” he said.

Murray said that before and during testing, the Navy stations someone on the ship to look for whales, dolphins or porpoises. Passive sonar and aircraft, if available, also are used.

If any whales or dolphins are seen within 1,000 yards the power on the sonar is turned down, she said. Within 500 yards the power is turned down more, and within 200 yards it’s turned off.

Sonar testing is specifically allowed by federal law off the coast of Washington, Oregon and Northern California, she said. It is not specifically allowed by law pierside but it is not prohibited, either, she said. It is not allowed in inland waterways or the Strait of Juan de Fuca, she said.

The Navy is applying for a permit that would specifically allow the testing pierside in Everett, she said. It would seek a waiver under the Marine Mammal Protection Act to allow some instances in which the sonar testing likely will in some way affect animal behavior.

Sonar is more essential now than ever in detecting newer, quieter submarines that are being used by more than 40 countries, according to a Navy website.

“Active sonar is the only effective means available today to detect, track, and target modern subs under all ocean conditions,” according to the site.

Bill Sheets: 425-339-3439; sheets@heraldnet.com.