Why do salmon counts vary from year to year?

October 2, 2010

By Laura Geggel

NEW — 1 p.m. Oct. 2, 2010

Salmon populations have booms and busts, just like the stock market. And, like the market, some salmon are experiencing a recession of sorts — some of it due to natural causes, and others because of human-related factors.

Issaquah Salmon Hatchery docents learned about salmon population trends during a training session Sept. 11 in preparation for tours and Issaquah’s biggest festival of the year, Salmon Days.

“We’re always trying to give our docents a little something extra,” said Gestin Suttle, executive director of Friends of the Issaquah Salmon Hatchery. “We’re always trying to learn more about the salmon. We always get questions that delve a little deeper into conditions.”

About 50 volunteers listened as Ed Connor, an aquatic ecologist with Seattle City Light, wheeled through a PowerPoint presentation and congratulated them on their perceptive questions regarding fish.

Connor, of Fall City, has studied fish in the Puget Sound region for 22 years. An easygoing man who loves to talk salmon, Connor can discuss his favorite underwater creature for hours.

I like fish,” he said. “They’re just fascinating animals to study. Most biologists love it because they like to fish, but I like working in rivers and streams.”

He studied biology as an undergraduate and concentrated on aquatic ecology in graduate school. Even his wife works in the salmon recovery business. Like her, he works with species of fish that have been threatened with extinction and added to the endangered species list  — chinook salmon in 1999, bull trout in 1999 and steelhead in 2007.

After working with salmon and trout recovery, Connor began to wonder why salmon and trout numbers varied from year to year. He began reading journals and learned about climate trends and man-made developments, like urbanization, and how they affect fish populations.

If climate and fish scientists can uncover a pattern about fish numbers, they could uncover the Holy Grail and predict salmon populations in years to come.

This knowledge could help salmon and harvesters alike. If salmon biologists know salmon are going to have a low year, they can push for more habitat restoration, since they know the salmon will need more help.

“It makes us aware in terms of management,” Connor said. “There are going to be times when fish populations go up. It might not be related to what we’re doing. We shouldn’t lose our vigilance and say, ‘Oh, the fish have gone up, we’re doing well.’”

Salmon by the numbers

Connor started his talk at the Issaquah hatchery with information about one of Washington’s most famous fish and an annual visitor at the hatchery — chinook salmon, also called king salmon.

The population graphs were one of the most telling parts of Connor’s presentation. Hatchery docents looked with interest at a sine-wave like graph charting chinook counts from 1967-2009. Chinook live for about four years. Every 20 years contained a boom and a bust of salmon numbers.

During the last boom, in 2007, about 1,700 Lake Washington-native chinook spawned. In 2009, that number dropped to about 700 spawners.

It turns out that salmon numbers might be related to ocean temperatures. In 1997, University of Washington scientists dubbed the term Pacific decadal oscillation, a cycle of warming and cooling of surface water temperatures in the North Pacific. The oscillation works like a cycle, much like El Nino or La Nina.

Fish are affected by this temperature change, as is shown by their population increases and decreases.

“When the north Pacific Ocean gets colder, we start seeing chinook coming back in larger numbers,” Connor said.

Salmon thrive in cold, oxygenated water and their numbers dip when water temperatures increase. Warmer water does not hold oxygen as well as cold water.

Instead of looking at salmon production on a large scale, like the UW scientists, Connor began looking at factors influencing fish in local rivers and streams.

Although records are sometimes hazy, salmon numbers have plummeted in the past century because of factors including major habitat changes, urbanization and commercial fishing. In the early 1900s, the Army Corps of Engineers changed the geography of the region’s waterways. Before the Montlake Cut of 1917, Lake Washington used to be a stagnant swamp and had waterline 11 feet higher than it is today, Connor said. Redmond used to be swamplands and the Sammamish River, which used to be deeper and have a slower flow, was modified.

“Things are completely different now,” Connor said.

In addition to a changed habitat, fish also face other challenges, including changes in ocean conditions, hungry sea lions that station themselves by fish ladders, invasive predators like large and small mouth bass in Lake Washington, and other habitat changes over time.

Historically, if salmon were experiencing a population bust due to ocean temperatures, they could survive it. Now, survival is harder.

“Normally, the fish would be able to get through those low cycles, but with the combination of degraded habitat conditions and urbanization, we really have to watch out for those periods,” Connor said. “They’re not going to make it unless we improve the habitat.”

Chinook and steelhead

Both chinook and steelhead are on the endangered species list.

Chinook are known to be upwards of 30 pounds of swimming muscle. Their numbers hit record lows in the 1990s, with less than 200 Lake Washington-native chinook spawning in 1993. But, in 2001, their numbers started to recover.

“It gave us a lot of ideas,” Connor said. “At least things can get better, things can rebound.”

The steelhead does not share the chinook’s success story. Their numbers are so low, people are worried they might be locally extinct.

The Issaquah hatchery raised steelhead salmon in the 1990s and early 2000s.

Although not as commercially popular as chinook salmon, steelhead fish were still a multimillion dollar industry and popular among recreational fishermen, Connor said.

In a strange twist of events, steelhead fish are genetically the same as rainbow trout. The main difference is that steelhead fish swim to the ocean, and rainbow trout stay within the rivers and lakes system.

Ocean conditions are so bad that many steelheads might be staying in local rivers and lakes, transforming themselves into rainbow trout.

This year, the rainbow trout population in the Cedar River spiked, though Connor said the theory that they are actually steelhead is still unproven.

Unlike chinook, which spend a few months in local rivers and lakes before heading out to the ocean, steelhead salmon can spend two to three years before swimming to the Pacific. This means that major floods can decimate several generations of steelhead.

“They’re much more dependent on fresh water habitat and flow conditions,” Connor said.

The decrease of steelhead could also be affected by hatcheries like Issaquah no longer breeding steelhead, he said.

Education and research about the factors affecting salmon production can only help fish in the long run.

“By finding out they’re being driven by these ocean cycles, the more we can understand about how we can get them back into recovery,” Connor said. “People think fish are so simple, but they’re not.”

On the Web

Find historic salmon counts here.

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One Response to “Why do salmon counts vary from year to year?”

  1. colin matthews on October 20th, 2010 12:38 pm

    could you tell me what is the average salmon breeding stocks for the river tamar
    in south west england or could you indercate what would be a good average breeding stock for salmon to keep a river with a good healthy stock of fish ?thankyou

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