Today is Opening Day for local boaters, and it also marks the year's first four-hour shrimp season in Hood Canal, which can bring out close to 2,000 vessels if the weather is good.

The sudden burst of activity could be a shock to the half-dozen transient killer whales that have had Hood Canal pretty much to themselves for the past three months. The orcas — dubbed the "slippery six" — have come in from the Pacific coast to feed on the burgeoning harbor-seal population in the canal, a natural fjord that separates the Kitsap and Olympic peninsulas.

State and federal officials issued a joint news release advising boaters how to behave when they spot whales, and volunteers were organizing to hand out the rules at docks and marinas.

Bottom line: Keep your distance.

Orca expert Ken Balcomb says he doesn't expect a problem in Hood Canal.

"I don't think it's going to bother the whales a bit," he said from the Center for Whale Research on San Juan Island, where the region's salmon-eating resident orcas can be seen year-round.

"There will be a lot of vessel traffic, which might be kind of novel to them. Certainly in the past four months they haven't had a thousand boats in there," Balcomb said. "But I don't think it's any big deal. The openings are short."

Most shrimpers probably won't even see the killer whales, he added.

"Those guys are slippery when you're trying to find them," he said, and the recreational shrimpers will be busy with their boats, nets and catch.

"Their natural behavior down there has been pretty stealthy. They might pop up on one side of the canal and then show up 14 minutes later three miles down. They ride along with currents — at times they're doing 8-10 knots."

The orcas' 14-week stay is unprecedented, said Rocky Beach, wildlife-diversity manager for the state Department of Fish and Wildlife.

"They're called transients for a reason," Beach said, joking that "if they stay there much longer they'll be called resident transients."

The Hood Canal seal population has built up over the years and hunting is good.

"There are a couple thousand seals at least," Beach said. "That's reduced here in the last three months. It's a natural thing: Killer whales eat seals. It's the balance of nature."

The life-and-death struggles go on mostly below the surface of the 60-mile-long, 3-mile-wide channel, he said.

"You'll see whales transiting a straight line and all of a sudden they'll take a dodge on their course — out and around — and then you'll see an oil slick on the water and smell the distinctive smell of seal blubber," Beach said. "Then the birds come to eat the tiny pieces of meat" that bob up to the surface.

Boat traffic can interfere with the whales' ability to feed, communicate and care for their young. One concern is engine noise, as they use hearing as well as their sonar-like echolocation to hunt.

Gray whales have also been spotted in Puget Sound this spring, coming in to search for food during the annual migration from breeding grounds off Mexico to feeding grounds in the North Pacific.

The number of grays making inland-water forays has increased in recent years, and sometimes the foraging is desperate. One young animal died of starvation near the Puget Sound Naval Shipyard earlier this week.

Opening Day for boaters is an 85-year tradition of the Seattle Yacht Club — an excuse to get out on the waters of Lake Washington, show off the boat and party while watching the Windermere Cup crew races through the Montlake Cut.

Boaters can, of course, hit the water any time of the year. "This is a celebration of the change of weather," club spokeswoman Karen Kenyon said.

For recreational shrimpers, the Hood Canal opening has traditionally been the first in Washington's inland waters. In the past 10 years the number of people turning out "has increased wildly," said spokesman Doug Williams at the state Department of Fish and Wildlife.

The deep-water channel also produces "really big prawns," he said. "It's considered the blue-ribbon shrimp fishery in Washington state."

The Hood Canal harvest this year will be limited to 75,000 pounds each for nontribal and tribal harvesters, he said — 150,000 pounds total with no commercial fishery.

Turnout might dwindle some because this year, for the first time, there are simultaneous openings all over Puget Sound, Williams said. A reduced turnout could also mean additional openings later in the summer. Currently, there are just four four-hour openings: today, Wednesday, next Saturday and May 18.