Day 2 Mouth of the Fraser
Friday, September 22, 2006
Out in the salt chuck, along the edges of the silt-laden plume of the Fraser, the sockeye wait.
Starting in August, about two million shimmering fish which hatched out of the gravel of the Adams River in the spring of 2003 congregate near the mouth of the river.
They no longer feed, but flash restlessly through the waters of the southern end of the Strait of Georgia, waiting for the call.
Since the beginning of their migration down the Fraser in early 2003, they have grown from tiny smolts six or seven centimetres long to mature adults averaging about 6.6 kilograms.
Feasting on plankton through the Gulf of Alaska, they have developed the succulent, red flesh prized by first nations since time immemorial, and subsequently by newcomers. Rich in oil and fat, it will sustain the sockeye in the weeks to come as they fight their way back to the spawning grounds.
But they wait, sometimes as long as six weeks, for the unexplained and soundless signal that tells them when to start their journey so that they can be where they must be before they die.
Scientists remain uncertain about how they know when to begin their ascent. It may be the height of the tides, it may be the length of the days. Only the late-run sockeye wait; other runs go straight up the river.
But in 1996, something changed: The late run went straight up, and some stocks suffered a 90-per-cent mortality rate before they reached the spawning grounds. This year, they have waited, and the mortality rate is expected to be between 10 and 20 per cent.
Mike Lepointe, chief scientist of the Pacific Salmon Commission, thinks the wait may be a way of improving their chances against a parasite called parvicapsula, which attacks their internal organs.
"All the fish in the Fraser pick up this parasite," he says. "If they pick it up and come in early, they die before they spawn, as opposed to having a parasite and coming later, so they could survive long enough to spawn.
"They probably have adapted to delay in the strait, where they aren't going to get the parasite."
When their wait is over, the sockeye start on a rising tide which floods the river as far upstream as the Mission Bridge.
Four years ago, some days saw an extraordinary 500,000 salmon pass Mission in a 24-hour period.
This year, they have peaked at a rate of up to 150,000 a day passing the sonic arrays which count them, and the past week saw about 30,000 a day. Some 500 kilometres of fast-flowing water separates them from their destiny.
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TRIP DIARY
People: The mouth of the Fraser River is rimmed by a working port, an international airport, agricultural land and intensely urban development in Vancouver, Richmond and Delta.
Landforms: The Fraser flows into the Strait of Georgia over a vast, silty flood plain, one that has advanced 25 km seaward over the past 10,000 years. The estuary wetlands are home to about 500,000 birds.
SOCKEYE LIFE STAGE
Physiology: Before the fish move from saltwater into freshwater, they undergo a change in kidney function to expel surplus water from the blood.
Behaviour: Sockeye stop feeding in marine waters before embarking on the run up to their spawning grounds and must rely on stored fatty tissue, muscle and organs for energy.
RISKS ALONG THE WAY: In the diagram below, each of the 100 fish represents 250,000 of the 2.5 million sockeye starting the journey. Watch over these 18 days how parasites, predation and fisheries cut into those numbers so only the fittest survive. Red fish represent today's survivors:
© The Vancouver Sun 2006