The Smell of a Healthy Salmon Stream

Story and Photography by Mark Hume

Back in the early 1990’s Ken Ashley was working on restoring watersheds in British Columbia when he began to wonder about the importance of salmon carcasses, which were so abundant in healthy salmon stream, but largely absent in rivers where runs had crashed. How important, he wanted to know, were the dead salmon to the health of the river?

A dead Chum Salmon lies on a river bank ready to contribute to the environment

At about the same time several fisheries researchers in Alaska, B.C. and Washington, began to ask the same question. The answer they came up with has led to a revolution in the way salmon streams are now being restored in the Pacific Northwest.

Mr. Ashley had taken note of the reek that hung over the best salmon streams in the fall, where dead and dying fish could be seen drifting in the shallows and lining the gravel bars. He saw bears carrying fish up onto the stream banks, eagles and flocks of sea-gulls fighting over scraps of flesh and aquatic insects swarming the stiff, grey bodies of dead salmon that collected along the stream bottom. It was like there was a cauldron of life on the boil. But in streams where the salmon runs had disappeared, while the air smelled sweeter, the gravel bars were empty of birds and other wildlife, and the streambeds were free of aquatic plants and insects. One system seemed richly alive, the other dead.

For anyone who spent time in the field the importance of salmon carcasses was pretty obvious, said Mr. Ashley, who is a limnologist and environmental engineer in Vancouver. They seemed to be at the base of everything.

Salmon carcasses, he figured, were enriching the entire system, not only feeding the bears and eagles, but providing nutrients mostly nitrogen and phosphorous – that stimulated aquatic plant and insect growth.

A century of logging, hydro developments and over fishing had led to massive depletions of salmon stocks. Could it be, Mr. Ashley, wondered, that in losing the salmon runs, the rivers had become so nutrient poor that the whole system was depressed?

To test his theory he got access to about 12 tons of salmon carcasses from the Tenderfoot Creek Hatchery, near Squamish, just north of Vancouver. Built in 1981 by the federal government, the hatchery was helping to restore spring salmon runs in the watershed. But the river was nutrient poor, which led to slower growth and lower survival rates for young fish. Mr. Ashley thought getting more salmon carcasses back into the river could only help. But how to move that many dead fish?

That’s when we came up with the bizarre idea of using a wood chipper, he says with a laugh. We sharpened the blades so that they were like sushi knives, froze the salmon and fed them in. It worked like magic.

Coming out the other end of the chipper were salmon carcasses shaved up so fine it was like it was snowing fish. Driving along the watershed Mr. Ashley and his colleague began blasting that material onto the river banks.

We could do a semi-truck load in no time, he said. The response of the ecosystem was almost instantaneous. Plant life along the river banks flourished, by spring insect populations had increased and soon the young salmon in the river were growing larger and more of them were surviving.

Mr. Ashley wasn’t the first to recognize the importance of salmon carcasses. Early work in the field was then being done by several scientific researchers including Thomas Kline, who in 1985 began studying how nutrients were transferred by salmon from the ocean to Alaska lakes; Dr. John Stockner, a B.C. limnologist who worked on Vancouver Island sockeye lakes, and Dr. Robert Bilby, chief environmental scientist for Weyerhaeuser, in Washington, who investigated the contribution spawning salmon make to the nutrient load in watersheds.

From plants to insects they all benefit from fish carcasses

About the same time Mr. Ashley was spraying chipped salmon on the banks of a river, Dr. John Stockner was having even more remarkable results by fertilizing some nutrient poor lakes on Vancouver Island. Using barges and low flying aircraft, Dr. Stockner was adding to the lakes the nitrogen and phosphorous that had been lost from the system when huge sockeye runs to the system had crashed. Later, fisheries scientists working on the Keogh River, on northern Vancouver Island,• used pellets, rich in nitrogen and phosphorous, to replace salmon carcasses. They also combined nutrient addition with new methods for restoring habitat and the impact was stunning. Soon swarms of Mayflies and caddis could soon be seen dancing over pools that had barely had any insect life before. The survival and growth rates for coho and steelhead smolts shot up. The Keogh became a widely talked about project and pretty soon fisheries scientists throughout the Pacific Northwest were buzzing over the exciting possibilities raised by nutrient restoration. In Oregon and Washington for the past several years fisheries projects have been taking the surplus salmon carcasses from hatcheries and spreading them along rivers, sometimes by dropping thousands of pounds of dead fish from helicopters and sometimes by using the wood chipper method first used on the Squamish.

This approach of adding nutrients is taken as a given now, says Mr. Ashley. It is not considered experimental any more.

Hal Michael, with Washington State Dept. of Fish and Wildlife, was one of those pioneers who began in the early 1990•••s putting salmon carcasses out on river banks. As the science solidified around the issue, he and others began pushing the concept. He says about 40 different river systems are getting the treatment in Washington now.

It is well established, he said. But there are problems. For one thing, many water managers regard the addition of nutrients to a stream to be a form of pollution. Water quality managers look at distilled water as being what they want, he said. And that’s a problem for fisheries managers because the crystal clear streams that are regarded as clean and desirable by the public, in fact are so nutrient poor they are unhealthy for fish.

We (in society) honestly don’t know what a healthy stream looks like any more, said Mr. Michael, because none of us was around when the salmon runs were at historic levels. What managers and the public think is a lot of fish in nowhere near what a lot of fish really is.

Another problem fisheries managers face is that there just aren’t enough salmon carcasses available from hatcheries to adequately fertilize the states many nutrient deficient streams. And, because of concerns about spreading pathogens, there are restrictions on taking salmon carcasses from one watershed and dumping them in another. The Washington Department of Fish and Wildlife is one of several agencies that is getting around the carcass shortage by using other methods to get nutrients back into salmon streams.

A bear chewed salmon carcass

Currently there are two methodologies in use, states the WDFW. One involves the introduction of liquid fertilizer into the water, either through intermittent dosages or through low-level drip. The second involves the placement of solid fertilizer pellets that dissolve at a predetermined rate, releasing nutrients over a period of months. Both methods have been shown to cause substantial increases in fish growth, survival, condition factors, and the like. Water quality monitoring associated with the application of these fertilizers has shown that they are rapidly taken up into the food chain and are generally not detectable in the water column outside of the treatment area.

Researchers have begun looking at the use of carcass analogs, blocks of nutrients, that are made from fish waste that has been treated to kill any associated pathogens. The idea is simply to reintroduce into salmon streams the nitrogen and phosphorous that was lost when salmon stopped spawning, and dieing, in such large numbers. Mr. Ashley says it doesn’t matter whether carcass analogs, or real dead salmon are used the important thing is to get nutrient levels back up to where they should be naturally.

This approach works. There’s no doubt about that any more, he says.

But overcoming the clear water paradox, the perception that crystal clear streams are clean and healthy, still remains a challenge. In a perfectly healthy salmon river, fish spawn and die in such numbers that they fertilize the river, stimulating plant and insect growth, thereby helping the young fish to thrive. A healthy salmon river, Mr. Ashly knows, is redolent in the fall with the scent of rotting fish. One day he hopes to smell that everywhere. Including on Atlantic salmon rivers.