Close call, but Hood Canal may escape a major fish kill this fall

With some luck, southern Hood Canal may avoid a major fish kill this year, as we observe extremely low oxygen levels beginning to dissipate.

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It looks like the fish around Hoodsport dodged a bullet on Friday when south winds pushed the surface layer of oxygenated water to the north, bringing hypoxic waters up from below, according to data from the Ocean Remote Chemical Analyzer (ORCA) buoy near Hoodsport.

University of Washington researchers watching the conditions issued this alert on Friday: “Hypoxic waters have been observed intermittently at the surface at our Hoodsport mooring — in addition to the Twanoh mooring —consistent with the strong southerly winds and upwelling conditions we’ve been seeing over the past few days.”

Seth Book, who monitors the water conditions for the Skokomish Tribe, said he was on vacation last week and did not make his usual rounds to observe potential fish kills. But we have not heard of any reports of dead or dying marine life along the shores of Hood Canal.

The risk of a fish kill is still present, and another strong wind out of the south has the potential to bring more low-oxygen water to the surface. The layers of water and the timing appear similar to last year, when south winds brought deep-water fish — such as ratfish — to the surface, as Seth recorded in a video. See Water Ways, Sept. 1, 2015.

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Each summer, sunny weather brings a growth of phytoplankton that eventually dies, sinks to the bottom and decays, a process that consumes oxygen. The result is extremely low levels of oxygen near the bottom of Hood Canal, a situation that continues until a surge of seawater in late summer or fall pushes in from the Pacific Ocean.

Because of its higher salinity, that seawater comes in along the bottom and pushes up the low-oxygen water, which gets sandwiched between the ocean water and the more oxygenated water near the surface. If the surface layer gets displaced suddenly by the wind, the fish have no place to go to get oxygen. That appeared to be the condition on Friday, but now the middle layer is growing thinner as it mixes with the layers above and below.

Conditions are improving, Seth confirmed, “but the negative side of me still says we have low D.O.” Crabs, shrimp and deep-water fish may be out of the woods for this year, thanks to higher levels of oxygen in the incoming seawater, but mid-level fish are still at risk until the water column equalizes to a greater extent.

In July, areas farther north in Hood Canal, such as Dabob Bay, experienced low-oxygen conditions, which drove a variety of fish to the surface, Seth told me. Of particular interest were thousands of Pacific herring trying to breathe by staying in the upper foot of water along the shore.

“We have dodged something so far this year,” Seth said. “I am hopeful because we are now into September and we can see this intrusion continuing.”

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