Salmon begin to diverge in behavior after emerging from the redds into two general groups of salmon. The first, “stream-type”, stay in the vicinity of spawning beds over the winter after emerging from the redds. They also return to fresh water months before spawning, typically from February through July. Spring and summer chinook salmon in the Columbia and Snake Rivers typically are regarded as “stream-type” salmon.
In the first year of life in the streams, perhaps 70% of the population is lost to starvation and predators. Birds eat many of them. Dr. Don Chapman is probably the world's greatest expert on the biology of Idaho salmon. Three times, most recently in 1988, he has received an award from the American Fisheries Society for publishing the most significant paper in the Transactions of the American Fisheries Society for the year.9 Dr. Chapman suggests that by killing colonies of mergansers in Idaho that can consume hundreds of juvenile salmon in a single day, one could cause an appreciable increase in the number of smolts emerging from any particular stream.
Perhaps in order to avoid this predation, juvenile chinook salmon tend to avoid still and clear water, avoiding beaver ponds and off-channel sloughs. Some have theorized that pools of water from beaver ponds, log blockages, etc., are essential to provide “overwintering habitat” for juvenile salmon. However, there does not appear to be much published scientific evidence to suggest that lack of pools is a limiting factor in chinook production, except where habitat is so degraded that water temperatures rise to undesirable levels.
Because stream-type salmon spend much more time in fresh water, they are more vulnerable to the loss of freshwater habitat and, as adults, to land-based harvest pressure. The stream-type of salmon that survive the birds, bull trout, and other problems begin to head downstream as the ice and snow melts. They move quickly, and do not linger in the mainstem rivers.
Once they reach the ocean, another important behavioral difference appears: the stream-type chinook are great ocean explorers. Indeed, samples of chinook salmon captured in the Western Pacific in Japanese fisheries are almost exclusively stream-type chinook. No one is really sure where populations of stream-type chinook salmon from Idaho go in the ocean. Although some tags have been recovered in Canadian and Alaskan fisheries, too few tags have been recovered to draw firm conclusions.
The upriver spring/summer chinook in the Snake River Basin have been in decline for some time, from 1.5 million in the late 1800s, to an average of 125,000 in the 1950s. Over the 1960s and 1970s and 1980s, wild fish in the Snake River seem to have been gradually replaced by hatchery fish. From 1980 to 1988, however, the population of wild fish rose from 3,343 to 21,870 fish,10 before crashing in the 1990s. According to the Idaho Department of Fish and Game, only about 60,000 wild spring chinook are expected to migrate out of Idaho streams in 1996, along with about 350,000 hatchery smolts.11
There are some encouraging signs, however. The population of “jacks” sampled in 1996 was the highest in years. “Jacks” are sexually precocious 2-year old males. Increases in their number typically signal larger returns of the more abundant classes three, four or more years old. And the number of returning adults has increased for three years in a row. The 1997 return of upriver adults is the best in many years.
9 Dr. Chapman’s qualifications are summarized in his affidavit filed Dec. 14, 1993, in Northwest Resource Information Center v. National Marine Fisheries Service, No. 93-870-MA (D. Or.).
10 PNGC v. Brown, 822 F. Supp. at 1483
11 B. Rudolph, “Huge PIT-Tag Study Planned by Long-Term Critics; NMFS Has Doubts”, Clearing Up, Dec. 23, 1996, at 5.
This Web page was created using a Trial Version of HTML Transit 3.0.