Scientists worry Hood Canal may suffer extensive fish kills

Scientists worry Hood Canal may suffer extensive fish kills

By By Craig Welch, Seattle Times environment reporter
22 September 2010

 

The bottom fish are at the surface once again, milling about in massive clusters along the upper reaches of Hood Canal, trying to avoid death by suffocation.

The quillback rockfish, copper rockfish, ratfish, Dover sole and eelpouts have moved up from the canal’s deep water in their seasonal trek away from an oxygen-starved dead zone.

But this year, if conditions don’t improve soon, this new location could prove exceptionally deadly, and to far more creatures than in recent memory.

Scientists have been warning for weeks that poor flushing of the canal last winter combined with the expected influx of deep ocean water may set the stage for substantial fish kills in the canal this year. Oceanographers and scuba-diving biologists said Tuesday that conditions are right on the edge.

"We’ve never, in recent years, seen it like this," said Jan Newton, an oceanographer at the University of Washington. "The thing that concerns us is that this could last for a while."

Monday, for the first time this season, a few hundred dead fish washed up along the shores of southern Hood Canal. This phenomenon has occurred virtually every year of the past decade, a combination of natural processes and increased pollution in the canal by humans.

By Tuesday, however, conditions had deteriorated, and low-oxygen water had also killed thousands of shrimp and several hundred more fish.

"I called Monday’s event a minor fish kill," Wayne Palsson, a fish biologist with the Washington Department of Fish and Wildlife, said Tuesday. "Today we woke up to a more extensive event — a few hundred dead fish here, a few hundred there. But this thing is still in its onset."

From Hoodsport to Potlatch State Park and then back up the canal’s hook to Twanoh State Park, low-oxygen waters over the past few weeks have driven fish to the top 20 or 30 feet of water. State divers a few weeks ago saw just three or four bottom-dwelling rockfish in one spot just below the surface. Tuesday, divers in the same spot saw dozens and dozens.

"There are hundreds of fish hanging out in shallow water where the current comes over the rocks," said Palsson, who dove into the canal to document fish movements. "They’re just sitting there with their mouths open letting the water pass over their gills. It’s quite a sight."

Every summer, algae blooms and then dies and decomposes, using up oxygen in the southern part of the canal. Eventually, winds and an influx of dense ocean water help flush this mobile floating "dead zone" out of the canal. Newton and other scientists recently determined that 10 to 30 percent of the nitrogen that fuels this dead zone is the result of pollution from humans.

But last year saw less upwelling of cold dense water into the canal, meaning less of the low-oxygen water got flushed out. As a result, by the end of this summer, the dead zone extends about three times deeper into the water column.

As dense upwelling Pacific Ocean water again begins to work its way into the canal, scientists are concerned it could push the low-oxygen zone closer to the surface — to the very place fish and other creatures come to escape the dead zone.

"We won’t know until we see what happens, but the fear is that the low-oxygen water comes to where the fish have been hiding out until things get better," said Al Devol, another UW oceanographer.

The scientists worry that, unlike the last major fish kill, which took place over the course of a few hours on Sept. 19, 2006, this one could last for days or weeks.

"The question is how much pain do the fish endure and how much damage will it do to the marine food web before it’s over," Newton said. "That’s what we are waiting to see."

Newton’s quick to point out that many factors are at play — it’s still possible that problematic conditions will subside before they worsen.

But for now researchers can only watch and wait, and see what each new day brings.

Craig Welch: 206-464-2093 or cwelch@seattletimes.com 

2010-09-28T12:08:00+00:00 September 28th, 2010|News|Comments Off on Scientists worry Hood Canal may suffer extensive fish kills