The Role of Chinook Salmon

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There are many indications that in the past, the Sandy River hosted huge runs of Chinook salmon. Of the five species of Pacific salmon, Chinooks are the best equipped to exploit highly fluctuating glacial/volcanic watersheds like the Sandy River basin. The same is true for most other river basins surrounding the Pacific Rim.

Chinook salmon populations have to be pivotal to the overall fishery management scheme in this river system. Spring Chinook are the largest spawning biomass in the upper basin. Fall Chinook are the largest spawning biomass in the lower mainstem. Therefore they are potentially the basis of the food chain for both trout and steelhead.

Chinook eggs, fry, and carcasses provide nutrients to the system, both directly and indirectly. Chinook spawn is ravenously consumed by all sizes of salmonids, cottids and minnows whenever they are available. Salmon carcasses are prey to all kinds of beneficial insects and plants, which are also consumed by other species of fish of many sizes.

Chinook fry are some of the earliest to emerge from the gravel. This emergence provides an early spring meal for trout and steelhead juveniles, which are two or more years older. Chinook fry are consumed by all fish that are large enough to eat them.

John Peterson, who was a fishery tech for the Mt. Hood National Forest, was in charge of the Still Creek fish trap. This trap is placed to capture downstream migrating fish. Most of the fish that have been caught in this trap are juvenile salmon, trout, and steelhead. A small sample of each species was killed for scientific study. These studies included stomach autopsies. John reported that most of the wild steelhead smolts were gorged on Chinook fry. No doubt resident cutthroat and rainbow trout partake of this same feast.

Spring Chinook fry emerge January through March. Fall Chinook fry emerge February through April. They are about 1-1/2 inches long when they become free swimming. Many Chinook salmon rear in the stream for less than one year before going to sea. Some start to migrate out immediately upon emerging from the gravel. Most are about 1-3/4 to 2-1/4 inches long when they enter the salt. By comparison, the average out-migrating steelhead smelt are usually 5 to 7 inches and may be over 10.

Chinook fry emergence is perfectly coordinated with the peak downstream migration of juvenile steelhead. Juvenile steelhead consume large amounts of Chinook fry on their way to the ocean. Chinook fry are large food, which permit the steelhead juveniles to grow very quickly and enables them to compete better in the ocean. Since the Chinook and larger steelhead are out-migrating together, this symbiotic relationship may continue for a while at sea. However, ocean rearing Chinooks tend to feed at much greater depth than steelhead and the two populations are soon parted.

Since Chinooks out-migrate at a comparatively small size, they probably don't compete much with other species for food or space while in the stream. They are a windfall profit in the food chain department. Basin populations of every other wild salmonid species are probably highly dependent on very large, healthy populations of spawning and emerging Chinooks. If we have more Chinooks we will probably have more of everything else.

Chinooks were the most abundant salmonid in the Columbia River basin. They were also the most desirable for table fare. They were highly exploited by indigenous populations of humans for thousands of years. They were soon over exploited by the present civilization to the point of near extinction.

This happened very early in our history. Records show that in 1877, there were over a thousand 1200' long gill nets and many fish traps working the Columbia River. All of the larger tributaries also had nets and traps. Most of the Chinook runs were on the brink by 1885. This is long before we kept records of wild fish populations. I think that all of the west slope rivers were much richer in all of their fish runs before the Chinook populations were reduced. The catastrophic reductions in Chinook runs probably brought a biological collapse to much of the Columbia River basin, both east and west of the Cascades.

Sandy River Chinooks were some of the first to be heavily targeted by commercial fishermen. The mouth of the Sandy is in close proximity to the largest population area. Nets and fish wheels probably killed most of the Sandy River Chinook runs before 1880.

A salmon hatchery was established on South Boulder Creek, a tributary to the Salmon River in 1892. This hatchery was to supply Chinook eggs to bolster the failing Clackamas River runs. Chinook eggs were taken from mid-July through November. There were fair numbers of fish. But what the hatchery people found at the mouth of South Boulder Creek in 1892 was probably no more than the remnant valleys, after the peak runs had been cropped to extinction. Old records speak of July spawning Chinooks in both the Sandy and Clackamas drainages. There is indication that in the first two years of hatchery operation; peak spawning activity was in mid to late August. These upper river runs had severely declined by 1900. By 1906, the runs were so poor that the hatchery was shut down.

In 1864, the vacuum packed tin can had been introduced to the Columbia River. Salmon could now be shipped long distances without fear of spoilage. Between 1864 and 1877 Chinooks were harvested so intensely that entire races were completely eradicated.

Before this 13 year harvest period, the spawning and fry emergence cycles would have been months longer and much denser than they are now. The overall food chain must have been immensely richer.

Marmot Dam was built on the Sandy River in 1911. It was a huge habitat and passage problem between 1911 and 1974. It impeded passage and killed downstream migrating juveniles in massive numbers. During the 1940's, the Sandy River Chinook runs were on the brink of total extinction. Runs had become nearly intermittent. Some years, less than fifty fish returned. Peak years brought runs numbering in the low hundreds.

From 1939 until 1951 the fish ladder at Marmot Dam was closed. All anadromous fish were eliminated from the upper Sandy River basin. Fishery managers realized that the unscreened flume entrance to the Marmot diversion canal was a death trap for a very high percentage of downstream migrating fish. Fish entering the canal eventually had to escape through the turbines in the Bull Run generators. Mortality was near 100 percent. Instead of forcing the power company to screen the canal entrance, they opted to stop migration of anadromous fish above the dam. They trapped all of the fish and took their eggs to be raised in a hatchery built below the dam. The project was a disaster. Runs further declined. They reached a low in 1943 when only 3 female Chinook showed up for egg take.

In 1951, the Marmot flume was screened so as not to entrap juveniles and the fish ladder was reopened. As Chinooks started to re-enter the basin, the run timing and spawning activity timing was very critical. This is because of the small numbers of fish available. Fish that reached sexual maturity too early or too late had a hard time finding mates.

In 1974, crucial water flow management improvements on the Sandy River brought about more favorable conditions for Chinook migration. The Oregon Department of Fish and Wildlife started an aggressive hatchery program with upper basin spring Chinook. Up to 420,000 spring Chinook juveniles are raised at the Clackamas River hatchery and planted in the Sandy and Salmon Rivers. These are from the lower Willamette stock of hatchery fish, which are mostly Clackamas River fish. In the 1890's Sandy River Chinook eggs were used to restart the Clackamas River runs. Now these same genetics are being used to restart the Sandy River runs. It's kind of like the genetics were on loan. These Chinooks have in fact adapted to the Sandy River better than they have adapted to the Clackamas.

Sandy River Chinook runs have prospered and grew in numbers through the 1980's and 1990's. The run of 1992 was estimated at 9,200 fish with an escapement of 6,000 spawners. Run timing has become less critical with both earlier and later returning fish able to find mates. In the past several years there is indication that our present spring Chinook runs are stretching out over slightly longer periods.

What was primarily a May and June run has now become a March through July run. Spawning used to be late September. Now some Chinooks are spawning from early September through late October. The food chain in once again getting longer.

The study of biological science assumes that if there is a niche, then some organism will fill it. Much of the Chinook habitat in the upper basin is nearly the same as it was in 1800. If this habitat is maintained in this same condition, it is reasonable to assume that Chinooks will eventually exploit all of it. It may be possible to once again have July spawning Chinooks in the watershed.

Marmot Dam was removed from the Sandy river in 2007. Now there are neither upstream or downstream passage problems at that location. Fish traps on tributary stream prevent hatchery Chinooks from spawning with wild fish. This program was started in 2008. Advocates and managers of this wild fish scheme claim success.

Fall Chinook spawn in the main stem and larger tributaries throughout the basin. The largest spawning concentration is from the mouth of the Bull Run River to Dabne Park. These runs are comprised of four genetically different races of fish. First to come are the Thule Chinooks. These fish are already colored when they begin to enter the river in late August. They are done spawning by late September. Next are the later bright Chinooks. They enter the river beginning in early October and are done spawning by December. Latest to come are the winter Chinooks. They enter the river December through January and may spawn as late as February. Dispersed through the runs are Columbia River Hatchery stray Chinooks. There has been no other hatchery intervention since 1977. Recent reductions in commercial harvest have brought better returns of Sandy River fall Chinooks. However, runs are still far below basin carrying capacity The 1995 run may have been 3,500 fish, with a basin carrying capacity of over 10,000.

Think of the biomass provided by 15,000-20,000 spawners in the upper basin, rather than 1,500-5,000 spawners... and another 6,500 Chinooks spawning in the lower river. The food chain in the river would be much richer. Every Chinook that spawns in the watershed is money in the bank.

To protect and anchor their eggs in the river bottom, female Chinooks dig depressions in the riverbed with their tails. These depressions are created by the tail being used as a shovel and also by the hydraulics being created by the oscillations of the tail in the water. The eggs are deposited with milt from the male Chinook in the bottom and trailing edge of the depression. The depression is filled and the trailing edge is mounded over with a layer of silt free gravel. This site is called a redd.

Chinook redds are often tipped up into the current. The rear interior wall of the redd is usually composed of sand and silt that has collected downstream from the digging. In a large excavation, this can form a mound that is three feet higher than the bottom of the depression. The mound often assumes a shape that is flattened or slightly cupped in the front and fan shaped at the rear. This mound is often called a sand dune. These dunes are most prominent in rivers which carry heavy loads of volcanic sand, such as the mainstem of the Sandy and Zig Zag, and the Deschutes below the mouth of the White River. This is because of the availability of building material. These kinds of rivers have plenty of sand to build mounds. However, this type of structure is also most efficient at keeping the redd from clogging with sand and destroying the water flow which oxygenates the buried eggs.

A layer of coarse rock is deposited on the tilted upstream side of this silt mound. The gravel is chosen so that it builds a strata that is devoid of silt and water passes through it easily. This porous strata is also designed to catch the eggs and milt as they flow from the spawning fish. This will become the interior of the redd. This is where the eggs will incubate.

Over this nursery is deposited a shield consisting of larger and larger stones. This layer also allows water to pass through it with little restriction. The heavy rock keeps the redd from eroding.

Water flows through the front wall of the redd and is deflected by the rear wall of silt. The water flows into the redd from the bottom and out the top. This keeps silt from collecting inside the redd and thus insures the complete oxygenation of the eggs. If the eggs were deposited in a depression below the level of the riverbed, they would quickly become buried in sand and smother.

Spawning pairs of Chinooks often join redds side by side in rows. The upstream edge of these elongated dunes often rises steeply from the riverbed. The upstream face of the dune is composed of coarse gravel and the backside is sand and silt. In areas where many Chinooks spawn together, these dunes may form rows which run perpendicular to the current flow. Between these dunes are trenches filled with soft flows. This washboard contour slows the water flowing along the bottom of the river. These are favored resting areas for several species of fish including trout, steelhead and whitefish.

The digging and shaping of Chinook redds creates gravel deposits which can later be used by smaller fish. Since Chinooks are early fall spawners, the gravel deposits that they create are already prepared for later spawning species such as steelhead, coho and trout.

Spring Chinook dunes in the Salmon River trap smaller gravel along the edge of the river. In the spring, this gravel is actively sought out by spawning pairs of winter steelhead. In the lower Sandy River, steelhead spawn in the leading top edge of fall Chinook dunes. The hydraulics created by the dune also keeps their eggs free from slit.

Since the Chinook redd is designed to allow water to flow through it, there are a lot of holes between the rocks which have been built it. These holes are prime habitat for many species of insects such as mayflies, stoneflies and caddis. Chinook spawning areas are very rich in insect life. Leeches and sculpins are also very prominent in Chinook redds. These organisms are food for various sizes of larger fish.

Historic records of hatchery egg takes show that the size of returning adult Chinooks has changed very little over the years. Sandy River basin adult Chinooks average fourteen to twenty five pounds, with some specimens up to forty pounds. The average steelhead is seven to eleven pounds. The average coho is five to eight pounds.

Chinooks are the largest salmonids that spawn in our watershed. Their larger size means that they can exploit larger gravel than smaller fish. Big Chinooks are powerful enough to move grapefruit size rocks around. This is a different part of the streambed than is utilized by steelhead, which prefer golf ball size gravel. Resident trout are only large enough to move marble size stones.

Chinooks spawn during the lowest flows of the season. This means that they utilize the center of the streambed. Their fry tend to stay in the middle, deeper parts of the river. They don't compete for food or space with other species, which spawn later in the season when river flows are higher.

Steelhead, trout and coho spawn in small tributaries or along the margins of rivers. Often they spawn in places which didn't have enough water when the Chinooks were spawning. Each species is designed to exploit a different size of gravel and therefore has different spawning habitat requirements. Their fry are also genetically designed to exploit this environment. They usually rear close to the redd through early development. In this way, the fry of different species tend to remain separated through infancy and don't compete with each other.

As trout and steelhead get larger they require more individual space. As they grow they seek deeper and deeper water. Older fish will often find holds in the middle of the river. Some of the best holding water is in the drop-off behind a series of Chinook redds. These areas are often very rich in insect life. Here, there is depth for cover and soft flows which make living secure and easy. This is also the prime area for intercepting emerging Chinook fry. Trout and juvenile steelhead migrate to these areas and there is often enough food and space to support large numbers. The larger fish rigorously defend the prime spots. Smaller fish patrol the margins.

Chinooks are big strong fish that are a challenge to catch and are good to eat. But, the importance of healthy Chinook runs go beyond just being grist for the human mill. They are an indicator species for the health of entire watersheds.

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