The first day of autumn - the Fall Equinox - is September 22. On that day, the hours of day equal the hours of night, but thereafter the light begins to fade.

Evening comes earlier on the stream, in the Pacific Northwest, and you can sense winter in the air. Mornings are frosty, but afternoons can still be pleasantly warm.

It is a time when furry, orange and black Woolly Bear caterpillars hurry across trails in search of the perfect overwintering spot - under a rock, or under a loose piece of bark. Ducks, geese, and other waterfowl noisily pass overhead, but the smaller summer resident birds like the swallows, vireos, flycatchers, hummingbirds and woodwarblers have long since fled south.

The foliage is transforming from lush green to a moulage of yellow, orange, crimson, and scarlet. The only flowers out are the bull thistle, goldenrod, yarrow, St John Wort, a few purple asters and a few buttercup. Crabapples are turning yellow and red, and beginning to taste sweet; as are the wild rose-hips. The smell of rotting pink and chum salmon carcasses hangs heavy on the air.

This is the time to think about catching bright, silver, Pacific coho on the fly, as they return from the sea. The average size and weight of mature coho varies from stream to stream, but in the Bella Coola River, on British Columbia’s central coast, for example, they average 4.5 kg, with a range from 1.3 to over 10 kg. A large coho can grow to be 98 cm (38.5 in) .

An adult, fresh-run coho is easily identified by black spotting confined to the back and upper part of a squarish tail. The general colour of the back is metallic blue, and this shades to bright silver along the sides and belly. Typically the gums are white, and the tongue is black.

After a week or two in the freshwater coho begin to transform into their spawning colours. The males become darker and develops bright red sides with bluish-green backs and heads. The upper jaw elongates, becomes strongly hooked, and teeth become greatly enlarged. The females undergo a similar, but not so dramatic transformation. In the spawning females, colours are not as vivid, and the jaw is much less hooked. Bella Coola

River coho begin spawning activity by October, spawning peaks in November and December, and is generally complete by February.

Spawning for coho, resembles that of other salmon and sea-run trout. The female coho selects out a nest site. Ideally the site is silt-free, has gravel size between 4 and 27 mm, and there is good circulation of oxygenated water through the spawning gravel. Typically she and her mate(s) will defend an area of about 12 m square.

Above and below the female coho, other females establish similar nesting territories. Around her, males fight and jockey for position, to determine who is most dominant. When ready to spawn she is joined by one or more males. The female digs out a nest by rolling onto her side and vigorously flexing her body and tail over the gravel lining her nest site. A depression is created - the redd - and into this depression she will lay her eggs.

At the time she is ready to lay her eggs, a dominant male - usually the largest and most aggressive male in the area - assumes a position close to one side and slightly downstream of her each time. Bodies quiver, mouths open, and the sperm and eggs are deposited simultaneously into the redd. The female moves upstream about 15 cm, digs out another redd, and the spawning act is repeated again, and again until all, or almost all the eggs are laid. Each time the female moves upstream the gravel she digs out of the newly created redd settles down over the eggs deposited in the redd located just downstream.

Over 75% of all eggs released by the female find their way into the bottom of the redd. The average number of eggs per nest averages around 800-900. The average number of eggs per female varies with size, but averages between
2500 and 3000.

After the female has deposited all her eggs, the males leave to attend other ripe females in the vicinity. The spawned-out female defends her nest site area until too weak to do so. The males continue to spawn until exhausted. From five to fifteen days after spawning, the females are swept away by the current and die. The males typically live a little longer, on average 5 to 30 days after spawning.

The eggs incubate in gravel over winter, alevins hatch from the eggs in early spring, and three weeks or so later, fry emerge from the gravel. Survival of fertilized eggs varies year to year, according to local streambed conditions. Crushing winter floods, and low flows with bottom ice can kill large numbers of eggs and alevins. Smothering silt deposition, fungus infections, as well as bird, fish, and insect predation also result in coho egg losses. On average, fry emerge from 15 to 30% of the eggs laid.

In extremely favourable conditions up to 85% of eggs will survive; under very harsh conditions 5% or less of the eggs will survive.

Typically the 30 mm long, coho fry emerge from the gravel at night. They initially aggregate with other newly emerged coho fry, hide in gravel when danger threatens, and then split up to establish freshwater territories upstream or downstream from emerging sites. The earliest emerging fry get the best territories, fry emerging later tend to move farther and farther downstream in search of adequate freshwater rearing habitat. Young coho are among the prettiest of the salmon and trout fry.

They have greenish-brown backs, distinct long narrow, black parr marks along the lateral line, and a reddish brown coloured tail. There is typically a white stripe along the leading edge of the anal fin, and orange tint on all but the dorsal fins.

Coho fry are very flexible in terms of the habitat in which they will take up residence. They will congregate in quiet backwater pools, side channels, small creeks, even along shores of lakes. Coho fry prefer slower pool water habitats, they do not tend to occupy riffle habitats - leaving this for steelhead, rainbow or cutthroat trout fry.

Coho fry eat a wide variety of stream and terrestrial insects. In fact, they will eat practically anything moving in or on the water column, provided it of an appropriate size. Chironomids, and other winged dipterans are among the most important foods of juvenile coho. In late fall, coho seek refuge from floods and killing anchor ice, by moving up or down stream into deeper pools, or into side creeks and tributaries that will remain clear and stable during the winter. Feeding virtually ceases during the winter months, as the juvenile fry are spending most of their time hiding motionless under the cover of logs, exposed tree roots, and undercut banks. Streams with this kind of winter habitat, will also have the highest coho winter survival rates.

Story by Harvey Thommasen with Photography by Nick Didlick