You, too, can observe oxygen changes in Hood Canal

I’m becoming something of a nerd when it comes to oxygen levels in southern Hood Canal. I’m sure it stems from the realization that we now have the technology to predict when fish will react to low-oxygen conditions by swimming to the surface, acting sluggish and sometimes dying.

Wolf eels at Sund Rocks in Hood Canal are disturbed by low-oxygen conditions.
Photo courtesy of Pat Lynch

In a story published in Monday’s Kitsap Sun, I took a step back from the immediate low-oxygen conditions and discussed our knowledge of Hood Canal, along with plans being formulated to address the low-oxygen problem.

Low-oxygen conditions reared their ugly head during the last week in September (Water Ways, Sept. 27). No major fish kills were reported before things began to improve somewhat by Friday (Water Ways, Sept. 30).

I’m keeping my eye on the charts and graphs and noticed a couple things that we can talk about. Compare the two oxygen profiles below with an eye to the surface conditions at Hoodsport (blue line) and deeper waters there below 40 meters.

Oxygen profile from Sept. 30
Oxygen profile today (Oct. 5)

The first thing I noticed was that the top of the hypoxic layer moved up from about 17 to 10 meters. That means if fish are avoiding that low-oxygen water, they will also move up. As far as I know, divers have not reported any observations to confirm or deny that change. One explanation is that the heavy ocean layer at the bottom is pushing up the entire water column. It also could mean that the surface layer has grown thinner, such as when south winds blow or north winds stop.

Meanwhile, the bottom of that middle hypoxic layer has moved up from about 70 to 50 meters and the edge has smoothed. That is an indication that the heavy ocean water, which contains more oxygen, is mixing with the bottom of the hypoxic layer.

One may also notice that the deep water at Twanoh (turquoise line) has become more oxygenated all the way through and is sharply higher in oxygen at the bottom. Perhaps this is an indication that the heavy ocean water has reached Twanoh and is mixing at the bottom, while winds and tides mix the water at the top.

University of Washington oceanographer Jan Newton has noticed a decline in the oxygen concentration in the middle layer at Hoodsport. She raises the prospect that this could result, in part, from low-oxygen water being pushed back from Lower Hood Canal by the annual intrusion of heavy ocean water. It needs to be checked further, she said.

I hope we get some diver observations this weekend or sooner. In discussing the current conditions with Dan Hannifious of Hood Canal Salmon Enhancement Group, we both wondered when deep-water fish will move back to their normal depth. What would it take for them to break through the middle low-oxygen layer to reach deeper water that is higher in oxygen.

If you would like to become an armchair observer of these conditions in Hood Canal, check out the graphs on the website of the Hood Canal Dissolved Oxygen Program. You’ll have to save old graphs to compare them closely, although another graph on the Nanoos website shows you changes in oxygen levels and other parameters over time for selected depths. (Click on “Regions” then “Puget Sound” and locate the Hoodsport buoy to find the graphs.)

Will the conditions in Hood Canal get better or worse this year? I’ll let you know, but if you see something unusual, feel free to post a comment here.

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