Stephen Hume: Heat wave adds to salmon’s migratory obstacles
Last straw? A tiny fraction of sockeye born in the Fraser River watershed survive the attentions of predators, animal and human. This year, add killer warm water to the mix
By Stephen Hume, Vancouver Sun Columnist July 5, 2015
The Early Stuarts, first of this season’s sockeye, are now ghosting in from the North Pacific, homing on the freshwater plume of the Fraser River.
It spills in a vast, silty lens across the Salish Sea, one of the last mysterious signals guiding them toward the final dangerous stretch of a 16,000-kilometre journey.
They will mass in the river mouth, then, a couple of weeks from now, turn into a current discharging just south of Hell’s Gate Canyon at a volume equivalent to one-and-a-half Olympic-sized swimming pools every second.
Mottled backs still a deep, glossy green, sides silver bright, soon to become deep crimson, this is the first of 19 sockeye runs to muster for the Fraser migration. The Early Stuarts have the longest distance to travel.
How many will return is the subject of arcane forecast statistics but federal fisheries scientists estimate a 50 per cent probability of only 30,000 Early Stuarts this year, less than 20 per cent of the average return of 162,000 on this spawning cycle.
Whatever the forecast, the reality for these perfectly evolved salmon is that they must battle the powerful Fraser’s current all the way to Prince George, then turn up the Nechako, then again up the Stuart to spawning beds at Fort St. James, a thousand kilometres from the sea.
Following the Early Stuarts come Early Summer runs bound for the Bowron Lakes in the Cariboo, Taseko Lake, the Adams River, the Nahatlatch, the Pitt and the Chilliwack. Next will come the Summer runs to the Chilko, the Quesnel River, the Horsefly, the Stellako on the Nechako system, the North Thompson and even a run of Late Stuarts — nature’s insurance policy.
Finally, the Late Summer runs will arrive bound for Cultus Lake, Birkenhead, the Shuswap, Seton Lake and Harrison Lake.
These returns mark the end of an odyssey beset by hazards from the moment this generation of sockeye emerged half a decade ago from the ice-clad gravel of spawning beds a thousand kilometres from the sea.
Of the 4,000 fertilized eggs deposited by a single female sockeye, only about 800 will hatch. Of the fry, only about 200 will survive to reach the sea as smolts. Of those, 10 will survive to adulthood. Only two will reach the spawning grounds where their lives began.
So these fish now homing on the plume of the Fraser are a surviving fragment — 0.25 per cent of those who set out.
As tiny fingerlings, they dodged hungry trout, larger coho and spring salmon, kingfishers, otters, terns, cormorants and lampreys on their way to the sea. Then they evaded a never-ending gauntlet of seals, flounders, gulls, sea lions, mackerel, sharks, dolphins and orcas.
Finally, as the survivors return to seed the next generation in the upper reaches of a Fraser River watershed the size of the entire United Kingdom, they are menaced by the kill zones of trollers, purse seiners, gill nets, reef nets, dip nets, sports anglers and all the ingenious, personal and industrial-scale killing technology of humans.
This year, there’s an additional threat — Mother Nature, herself. As forest fires rage and the rest of us swelter, even the mighty Fraser suffers. Snow packs were zero in many tributary watersheds.
Normally, snowpacks melt slowly at higher elevations, replenishing rivers with cold water during the hottest summer months, crucial for salmon which can’t survive high water temperatures.
Absent snow packs mean lower, warmer water in B.C.’s Interior. Hot conditions mean multiple threats to fish. This year, with drought prevailing for months — more than 64 temperature records were broken across the province in late June — snowpack benefits are mostly gone.
Feeder streams are drying, water levels are falling and temperatures are rising. Above 20 degrees, water is into the lethal range for migrating salmon. In the main arm of the Fraser between Richmond and Delta, water temperature Friday hovered at 19.8 C.
Temperature is just one of emerging threats. Warm water increases vulnerability to disease. Shallow water increases vulnerability to predators.
If water passing through Hell’s Gate Canyon is low enough, as it was in 1941, the force of the current jetting through debris left by railway construction in 1913 can become impassable to salmon.
That year millions of sockeye died in the canyon. In 1941, only 61 spawning sockeye were reported on the Adams River, now the iconic symbol of British Columbia’s salmon abundance.
Think of the miracle of fishes in which you are about to partake the next time you sit down to dine on your maple-rubbed, cedar-planked sockeye filet, fresh from the barbecue.
