Lakes, rivers vital to fishery

Productivity issues at heart of maintaining sustainable resource

Posted: Thursday, July 19, 2001

At the Alaska Department of Fish and Game office on Kalifornsky Beach Road near Soldotna, a team of fisheries biologists works to balance today's demand for salmon catches with tomorrow's sustainable yields.

They do so by guarding the productivity of the Cook Inlet salmon through escapement, regulation, research and habitat protection. Most of their focus is on the valuable sockeyes and kings and on the Kenai River system that produces 40 percent of the inlet's salmon.

"It's a pretty diverse watershed. That is one of the things it has going for it," said Jim Edmundson, a Fish and Game biologist.

Salmon grow in two distinct habitats, fresh and salt water, that have about equal input into a fish's survival, he said. The balance varies by salmon species, because each divides its time differently between the two. For example, silvers spend most of their lives in fresh water, while pinks are nearly totally ocean-going.

Edmundson specializes in the study of peninsula lakes, especially Skilak Lake, which serves as the prime nursery for Kenai River sockeye fry.

The area has three kinds of lakes, he said: glacial, clear and stained, which is usually the color of tea from peat and other organic materials.

"As a general rule of thumb, clear lakes are more productive than glacial lakes. You need two things: nutrients and energy (to support juvenile salmon)."

Suspended glacial silt makes lakes turbid, and the clouded waters block sunlight that fuels phytoplankton, the microscopic plants at the foundation of the food chain. As a result, small, clear lakes are more productive for their size than big glacial lakes. For example, small, clear Hidden Lake and enormous, glacial Tustumena Lake have about the same amounts of water available to photosynthesis, he said.

Plankton crops in a clear body like Upper Russian Lake are about ten-fold higher than those in Kenai Lake, he said.

Young sockeyes feed almost exclusively on zooplankton, the tiny animals that feed on the phytoplankton. On the Kenai Peninsula, those are usually two types: water fleas or copepods. The water fleas are more nutritious than copepods, but copepods are the only ones that will grow in silty lakes.

Edmundson said getting enough food seems to be the main factor limiting young sockeye survival.

In the early 1980s, the state experimented with boosting salmon smolt production by fertilizing lakes to encourage plankton growth. The plan was to replace nutrients because fisheries reduced the number of wild fish carcasses in the system. The program did get results, he said.

"On the average, we doubled algal biomass," Edmundson said. "What is hard to get at is did that contribute to greater returns? That could be offset by poor ocean survival."

Fish and Game stopped fertilizing lakes in 1997 as a result of budget cuts, but Cook Inlet Aquaculture Association continues to do two small lakes (Bear near Seward and Leisure, also known as Poot, south of Homer), he said.

In the late 1980s, salmon entering the Kenai River exceeded escapement goals because of combined strong runs and commercial fisheries closures due to the Glacier Bay and Exxon Valdez oil spills. In the years that followed, sockeye fry did poorly. Research suggested that the high population of juveniles ran out of food, he said.

When fry are sparser, they tend to be bigger and survive winters better.

About 50 percent of all sockeyes from the Kenai system come out of Skilak Lake, despite its harsh environment. Most young fish go there for the winter. Sampling results suggest that fry populations in Skilak and Kenai combined range from about 10 million to 40 million. But above 20 million, the quality of the brood suffers.

"Once you start loading up the system, the size of the fry goes down," he said.

In recent years, Edmundson and his colleagues have noticed a worrisome trend.

"What it looks like to me is that in Skilak Lake the turbidity levels are increasing," he said.

Warmer weather, increasing glacial melt and silty runoff, could be responsible. At the same time, the concentration of zooplankton has dipped 30 percent.

Biologists don't know if the plankton decrease is because of the cloudy water or from more sockeye fry in recent years. Nor do they know if the change is short or long term. They worry that the changes could foreshadow a decline in sockeye production from the river system, he said.

One step up the food chain, the lake salmon themselves, especially when still eggs, fall prey to sticklebacks and Dolly Varden char. Sometimes, when the smolts school up during out-migration, they attract hungry sea gulls.

"We have very little information on predators in these lakes," Edmundson said. "I don't think predation, per se, is an overwhelming factor."

Down the hall from Edmundson, fisheries biologist Tim McKinley researches the productivity of king salmon in the Kenai.

"What makes the Kenai unique is the quality of the fish and the size of them," McKinley said.

The returning adults tend to be sea bright, big and concentrated, compared with those in other rivers.

The Kenai kings tend to return when they are older and, therefore, larger. This behavior and the size that goes with it are mostly inherited, he said.

The biologists speculate that the Kenai favored large fish because they are competing for limited spawning space. Late-run kings confine most of their spawning to a few sections of the river. During underwater turf battles, large fish win, he said.

Once hatched, the king fry lead very different lives from sockeyes. Juvenile kings live in the main river or its tributaries and feed on insects. Food and cover are vital, but insects seem plentiful, so they probably have enough to eat, McKinley said.

"What controls king production, we don't have as clearly defined," he said.

Kings seem particularly sensitive to environmental quality. They use near-shore habitat, hiding among vegetation and under overhanging, vegetated banks. Their shyness may protect them from predators such as trout, Dollies, sculpins, mergansers and kingfishers, he said.

Keeping track of 3-inch juveniles is a challenge, so much of their lives remains unknown. One mystery is the kings' winter activities.

"We don't have a clear picture of that," he said. "They are hard to find in the winter. Some actually go back into the gravel."

Humans trampling riverbanks are bad news for little kings, so preserving banks is an agency priority.

"That is what we are trying to do with some of the closed areas," McKinley said.

Tributaries are vital as well as the mainstem. About half of all early-run kings spawn in the Killey River, which is protected, since it lies within the Kenai National Wildlife Refuge. Large numbers also spawn in Funny River, he said.

McKinley stressed that maintaining good habitat is the best way to assure fish for future anglers.

"There is a lot of good money, effort and work put toward restoration. But it's the Humpty Dumpty thing. It's hard to put it back the way it was."

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