Jul
31

Warm Water, Low Oxygen, Dead Salmon

If you have seen or heard any print, visual or audio media in the past couple weeks, you know something about the effects of this Northwest summer’s heat and drought on our fish, and our fishing.

You have likely seen the photos and video of dying sturgeon on the Columbia – 20- to 40-year-old fish suddenly unable to survive. You may have read that half of the salmon heading up the Columbia to make more fish (our future fisheries and food) are severely stressed and dying.

If you – like many of us in Paradise – look forward to summer fishing for salmon and all the other fish which bring us pleasure on the water and at the table, you have probably shared my dismay at the rise in emergency closures related to low flows and high temperatures.

Over the last couple weeks, in our region alone, the Upper Columbia River has been closed to sockeye salmon retention (Rocky Reach to Chief Joseph dams), along with the Wenatchee, Icicle and a reach of the Okanogan. Other closures include all forks of the Teanaway and the Little Naches. Fishing in a number of creeks and lakes (including Lake Wenatchee) was shut down to protect stressed fish stocks. The Naches River (Tieton to Bumping/Little Naches) and Rattlesnake Creek are under “hoot-owl” restrictions, meaning fishing is allowed only between Midnight and 2 p.m. Hatcheries around the state are taking strong measures to protect young fish. It’s a difficult year for those among us who live in water.

(Not all is bad news: fisheries pros determined that the sockeye going up the Wenatchee River into Lake Wenatchee are in good shape, and opened the lake’s sockeye season yesterday with a daily four-fish limit.)

I reached out to homey and fish pro David Child (www.dreamflyfishing.com) for his take on this summer’s fishing and he suggested I have a chat with Tobias (Toby) Kock, Fishery Biologist at the Columbia River Research Laboratory. Toby and I had an interesting chat, and he sent me fodder for some future looks at fish and river changes likely coming down the road.

This summer, he and his group have noted sockeye moving into cooler tributaries between dams as the worked upriver to spawning areas – a behavior common with late-summer steelhead and kings, but rarely seen with early salmon. They are also seeing a great many fish suffering from columnaris bacterial infections (also known as cottonmouth), which shows up as frayed or ragged fins, ulcerations and fungus-like white patches on skin and gill filaments. Much like many human illnesses which only flare up when we are stressed, columnaris is ubiquitous, but generally harmless in cool fresh water, becoming deadly as water temperatures rise. While it is unclear what has killed the dozens of adult sturgeon found in the Columbia lately, temperature and disease factors are no doubt involved there, too.

Looking ahead, Toby noted that, since water temperatures are normally higher when steelhead and summer Chinook head upriver, they will probably encounter somewhat more typical conditions than what our sockeye found. Coho are a later fall fish, and those conditions remain to be seen – or even predicted.

The oxygen/water temperature relationship is critical to fish survival. Fish have to breathe, just as the rest of us, and their gills enable them to extract dissolved oxygen from water.

Here’s a short primer: Oxygen diffuses into water and is held as dissolved oxygen. The amount of oxygen water can hold depends generally on atmospheric pressure and water temperature. Salt water can hold less oxygen than fresh water. At 20 °C (68 °F) and average pressure, 9 mg/l of oxygen can dissolve (8 mg/l in salt water). These are 9 ppm and 8 ppm, respectively. The amount of dissolved oxygen drops by about 1 mg/l for each additional 10 °C increase in water temperature. Cold water fish (like our salmonids) will be stressed as oxygen concentrations fall below 8 mg/l. Warm water fish (bass, perch, catfish) reach that point at about 5 ppm of dissolved oxygen. Oxygen levels will change through a day, given weather, temperature, sunlight and living or decaying plants in the water, and algae or organic sewage can quickly draw oxygen from water. (You will find a lot more information online at Wikipedia or any of a dozen sites.)

So, this summer we look at drought, warm water, low oxygen and dead or dying fish. If this summer is a harbinger of what is to come, then significant changes in how our rivers and their flows are managed will be needed. Over the past few decades, river management for irrigation, fish and people has become a fairly stable science. What we see this summer is not just about salmon – it may be a heads-up for bigger changes than we anticipate.

But that’s another day’s story.

Written by Jim Huckabay. Posted in Uncategorized

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