By Harvey Thommasen, with Photography by Nick Didlick

Of all the salmon stocks in the Pacific Northwest, the one that has adapted to human impact the best has been the pink salmon (Onchorhynchus gorbuscha). Pink salmon outnumber all other onchorynchid species combined by at least a ratio of 10 to 1.

To say pink stocks are healthy would be an understatement. On the Bella Coola River, in British Columbia’s Central Coast, where I like to fish, for example, the target escapement is 1,000,000 pinks.

There are many different reasons why pink salmon are such a successful salmon species. Pink salmon have the shortest life cycle of all the onchorynchids - 2 years - so they mature faster and spawn more often than the other salmon and trout species.

Pink salmon spend very little time in freshwater habitats so they are not as vulnerable to the habitat degradation that is so widespread in our Pacific coastal valleys. Last, but not least, their flesh is not as prized as some of the other salmon so the economic incentive to kill is not as great.
Pink salmon, however, are very important to the ecology of birds, mammals and the other fresh-water fish species in Pacific watersheds.

For example, each year spawning pink salmon will deposit an average of 800 million eggs (126,400 kilograms) into the gravels of the Bella Coola River. In an average year, 61.2 million pink salmon fry (14,872 kilograms) will hatch and emerge from the gravels. Of these, 28.2 million fry (6,853 kilograms) will eventually make it to the estuary. The "cost" involved in producing this many fry is impressive.

Approximately 1.5 million kilograms of adult pink salmon flesh and bones, approximately 117,000 kilograms of pink salmon eggs, and approximately 8,000 kilograms of fry will be left in the Bella Coola River system to be consumed by a variety of animals (vertebrates, invertebrates, and microorganisms).

Adult pink salmon begin moving into the Bella Coola River by the third week of July, peak return occurs around the second week of August, and a few fresh fish are still entering the system in September. Even year fish tend to arrive a week or so earlier than the odd year fish. Roughly the same timing is found in watersheds throughout the Pacific Northwest.

Spawning begins in August, peaks in mid-September and is finished by October. There are at least two or three discrete pink salmon spawning populations (stocks) in the Bella Coola. Pink salmon can be seen spawning from the tidal waters of estuary, all the way up the Bella Coola and on the Atnarko River to an area just above Lonesome Lake. They also spawn in many side creeks - Thorsen, Snootli, Nooklikonnik - and in the lower portions of Salloomt, Nusatsum, Noosgulch rivers.
The average adult pink salmon weighs 2.2 kg (1.5 to 4.5 kg). When the pinks first come into their spawning streams they have metallic blue backs, silvery sides which shades to white on the belly. Females and males look virtually identical. Large, black, oval spots are present over the back, upper sides and tail. They are beautiful fish, and when fresh in from the sea they come readily to a fly. With the right fly gear, say a 5 weight rod, these bright pinks salmon are powerful solid fighters.
Within a day or two of entering freshwater, the transformation for both male and female into their spawning form begins.

Within three or four weeks the transformation will be complete. The overall color darkens, scales become absorbed, the skin thickens, the meat undergoes lysis and becomes mushy, and the digestive organs atrophy. The metallic blue-back becomes a dark brownish or dark greenish-gray color. The silver sides becomes more of a pale slate, or greenish-gray color, while the belly becomes more pale white. The male gradually develops a conspicuous hump-shaped back (hence the name "humpy"), the body becomes laterally compressed in shape, the jaws become hooked and a dark reddish to yellow stripe appears along the sides.

The female lacks the striking secondary sexual characteristics of the male. Her body form becomes a bit more laterally compressed, her overall body color darkens, and the sides of the female tend to be a more greenish color than are the sides of the male. The lateral compression seen among spawning pink salmon is felt to be a useful adaptation for spawning in high current velocities.

Studies suggest that pink salmon tend to spawn in stream flows that exceed 0.7 m/s, and will spawn in currents up to 1.5 m/s. The highly visible, more conspicuous "hump" found in males may serve to attract predators away from the females.

That is, the predators see the males more readily so they feed on them more often, which in turn means more females are spared predation and are available for spawning. In the general scheme of things, one male can spawn with many different females so it makes males more expendable than females.

Each mature female will lay an average of 1600 eggs (range: 1200 to 1900). Approximately 51% of the eggs are properly buried in the gravel, and of these only 15% will survive to emerge as fry. Birds, insects, snakes, raccoons, otters and fish all feed on the eggs. Some predation takes place only on the eggs that drift free, but many animals also burrow into the gravel to feast on the eggs.
Beginning sometime in late March, peaking sometime between April 5-20, and ending some time around early May pink salmon fry emerge from the gravels. Most often, emergence from gravel happens at night - presumably this is a way to minimize predation.

The pink fry are 28 to 35 mm in length, weigh 130 to 260 mg, have a bluish-green back, very silvery sides and a whitish belly. Unlike other salmon and trout, juvenile pink salmon lack parr marks (dark vertical bars) along their sides. Parr marks serve to camouflage juvenile salmon and trout while they spend a year or two rearing in freshwater stream environment. Since pink fry head out to ocean almost immediately after emerging from the gravels, they do not seem to need the protective parr marks seen in these other fry.

Initially, newly emerged pink salmon fry hide under rocks, and do most of their migrating under the cover of night. But as they mature, pink fry gradually give up solitary nocturnal traveling and begin to aggregate into large, downstream moving schools. Typically these large schools travel downstream near the surface and in the centre of the stream where currents are greatest. Some anglers have reported the moving mass of pink fry as a “black cloud". They can be seen day and night. Pink fry migrating from lower tributaries likely reach the estuary in one evening, those beginning far up a system will take several days. Trout can sometimes become so stuffed feeding on pink fry that they will sink to the bottom and just lie there for days. But if you are lucky enough to be on a pink river as the emergence starts you can have phenomenal fishing.

A few pink fry may stop to feed on dipteran larvae (particularly chironomid), and other small aquatic insects larvae (stoneflies, mayflies, copepods, freshwater cladocerans) larvae on the way downstream to the estuary, but the vast majority do not feed until they get to the estuary. Unlike other salmonid and trout fry which will hide under stones or debris when attacked, pink fry rarely evade predators by seeking cover once they have formed schools. Because of this strong schooling behavior, pink salmon fry are among the most vulnerable onchorynchid species both in the river and while they are out in the estuary. Not surprisingly, outmigrating pink salmon fry are important food for sculpins, coho salmon smolts, dolly varden char, cutthroat trout, juvenile steelhead, rainbow trout. The occasional adult steelhead will also eat these outmigrating juvenile pink salmon - sometimes gorging on them.

Above water predators include crows, dippers, mergansers, gulls, mink, and kingfishers. All in all, the sculpins, coho smolts, and cutthroats are probably the most important overall predators of pink fry.

Studies have shown that a relatively fixed number of pink salmon fry are eaten by a relatively fixed number of predators each year. This becomes important in years of low pink salmon production. In years of low pink fry abundance, up to 85% of the population is lost to freshwater predators. In years of high pink production as few as 25% of the pink salmon population is lost to these predators. Overall freshwater survival (predation plus environmental mortality) for pink salmon ranges can range from 1% to 17%, but usually averages 6%. Most Bella Coola pink salmon fry are in the estuary by early May. There they spend four to six weeks before heading seaward. During the day, schools of tens to hundreds and thousands of fry can be seen foraging along the irregular shorelines in shallow waters only a few centimeters deep. Peak feeding activity occurs at dusk. When it is dark, the schools move offshore to spend the evening in safer, deeper waters. I have often thought this would be a good time to search the beaches with a fry imitation, looking for foraging searun cutthroat. Pink salmon fry grow rapidly while they are feeding along the shores of the Bella Coola estuary.

In fact they are among the fastest growing Pacific salmon species. They arrive in the ocean at a time of maximum zooplankton abundance, and feed heavily on the eggs and larvae of these tiny crustaceans, mollusks,larvaceans, and fish. Favorite foods include copepods (eg Calanus glacialis), euphausiids, tunicites (eg Oikopleura spp), waterflea larvae (cladoceran spp), and barnacle larvae (Cypris spp), molluscan pelecypod larvae, eulachon and herring fish larvae. Bella Coola pink salmon fry grow at an average rate of 0.87 mm/d during the first 30 days in salt water. They enter the estuary at or slightly above 30 mm in length, and leave shortly after they reach 45 to 55 mm in length. (Sizes worth keeping in mind when you tie fry imitations.)

Sometime around the end of May, schools of 500 to 2,000 pink salmon fry begin to actively move west out through Burke Channel and FitzHugh Sound. By June, the schools have reached the open ocean and are migrating rapidly (6 - 20 km/day) northward along the British Columbia and Alaskan coast line.

In general, pink salmon migrate in a broad counter clockwise circular fashion - north and northwest along the continental shelf, west and south out on the high seas of the North Pacific Ocean, before heading back to their home streams. They will spend approximately 12 months in the open ocean, and cover distances of 5,000 to 7,500 kilometers. Most feeding and traveling takes place in the top 30 feet of water surface. Feeding is primarily diurnal with peak activity occurring near dusk or at night. As pink salmon grow in size, they begin to feed on larger prey than that eaten by juveniles. Fish, squid, euphausiiids, and amphipods are the major pink salmon food items out in the oceans. By the time the maturing adults return to the Bella Coola River they average 55 to 60 cm in length, and weigh around 2.2 to 2.5 kg. During the last month or two at sea, homeward bound mature adults have been clocked at rates of 43.5 to 60 km a day.

Marine mammals known to prey on free-swimming pink salmon include the harbour seal (Phoca vitulina), the northern fur seal (Collorhinus ursinus), killer whales, the Pacific whitesided dolphin (Lagenorhynchus obliquidens), and the humpback whale (Megaptera novaengliae). The overall natural marine mortality rate for pink salmon approximates 95.7% of the fry that emerged from the gravel. Adding a 65% fishing exploitation rate on pink salmon that reach coastal waters total marine mortality approximates 98.2%!

Measured marine survivals for pink salmon from emerging fry to adults returning to the Central Coast Streams ranges from 0.2 - 5.2% with means of 1.8%. Of the estimated 122 fry which will emerge from the 1600 eggs deposited by the average adult female pink salmon, an estimated 56 fry make it to the estuary.

On average, 18 fry will survive to make the trip out to the ocean. Only two (range 0 - 6) will make it back as spawning adults! Those statistics are worth keeping in mind when you hook one. Handle it gently and let it go. Even if there are lots, they are still worth protecting. Without them our watersheds would be so nutrient poor they would almost be barren of life.