Scientists say a bloom of deadly "brown tide" that makes a surprise visit to Washington's inland waters a few times each decade, killing fish and then quickly heading out to the ocean, swept through the area last week.
SEATTLE — Scientists say a bloom of deadly "brown tide" that makes a surprise visit to Washington's inland waters a few times each decade, killing fish and then quickly heading out to the ocean, swept through the area last week.
The brown tide is blamed on an single-celled organism called Heterosigma that sometimes blooms in late June or early July when water conditions are just right. This year's plankton bloom was the first major event since 1997, but not nearly as bad as an occurrence in 1991, when fisheries reported millions of dollars in dead fish.
"We lost a small percentage of our fish. This wasn't anything like '89 or '91," said Kevin Bright, a biologist who has worked for American Gold Seafoods in Anacortes ever since they lost most of their stock in net pens during the 1989 plankton bloom. He would not be more specific about the number of fish killed by Heterosigma this year.
Farmed salmon are particularly vulnerable because the fish can't swim away from their pens when the wind or current pushes the plankton blooms to them. Scientists said wild salmon are also threatened by the organism because other fish swim deeper to avoid the plankton that stays close to the surface.
Researchers believe Heterosigma kill fish by lodging in their gills and suffocating them.
Bright said scientists have gotten some good ideas about how to lessen the impact of Heterosigma in the past 15 years and his company probably saved some of its fish by watching the water closely and knowing the right time to stop feeding them.
Somehow, starving the fish helps them fight off the impact of the plankton.
"It's sort of like running a marathon with a steak and baked potato in your stomach, it's not a good idea," Bright said.
He said this year's plankton bloom was widespread, from Canada's Georgia Strait to the Strait of Juan De Fuca, the San Juan Islands and Anacortes. From the air, the water contained large areas of water that had a coffee brown color on the surface and redder sections near the shore.
Rita Horner, senior researcher at the University of Washington's School of Oceanography, who has tracked Heterosigma for about 40 years, said this year's bloom lasted about a week.
Horner said she heard reports of lots of fish being killed this year, but none of the commercial fish farms told her how many fish they lost and fish kills in the wild are difficult to measure.
Warm temperatures, a certain percentage of fresh water in the marine waters -- usually caused by rivers filled with early snow melt -- and calm weather all seem to encourage the plankton blooms.
Unlike some other algae blooms, Heterosigma doesn't affect human health. In the past, the state Health Department has allowed fish killed by the plankton to be sold and eaten unless it had signs of bacterial decay.
"As far as we know, there's no danger to humans and probably not a danger to other organisms, either," Horner said. She said, however, that the plankton does appear to kill other kinds of algae.
She said the Heterosigma bloom doesn't arrive on a regular schedule and that Washington's marine waters can go years without a major breakout, or it could show up twice in one year.
"It could come back next week if conditions are right," Horner said, adding that some of the plankton may still be spreading off the Pacific Coast where fish could be dying but no one would notice because the water isn't being tested regularly.
She said it is difficult to study the plankton and hard to gauge its impact because it dies quickly under laboratory conditions and the only people keeping a close eye on it are biologists like Bright who work for fish farms.
Jack Rensel, an independent scientist who tracked the most recent Heterosigma bloom for the National Oceanic and Atmospheric Administration, said early July and early September are common times for the plankton to bloom.
Horner said the single-celled organisms, which scientists sometimes call the "hidden flora," may always be present in low concentrations in the region. The blooms were first discovered on the Pacific Coast in the 1960s. The algae also has been a problem on the East Coast and in the Pacific Ocean near Japan.
Source: Associated Press
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