Using Salmon Forage To Predict Runs
March 14, 2013
Predicting runs of salmon, like this Olympic Peninsula silver, into the Columbia and other Northwest rivers just became a little more accurate. The idea is to prevent collapse, something that's been hovering around the corner for decades.
Fishery managers have been making predictions for many years, in an effort to control harvest by fishermen. Historical estimates of the salmon runs into the Columbia each year fluctuate between 11 and 16 million wild fish between 1775 (when Spanish explorer Bruno de Heceta became the first European to sight the river) and 1800. By the 1890s, farming, mining, logging, and fishing already began to take a toll on those massive runs, according to Bill Bakke of the Native Fish Society. Runs today are estimated at somewhere between 1 to 2 million, with maybe 80% of those fish raised in hatcheries.
Silvers or coho salmon, like the fish in the photo, have been tragically overharvested in the Columbia until, today, they're found only in a "few streams" of the Lower Columbia Basin. Normal mechanisms for predicting the size of salmon runs have included ocean temperature, river temperature, spawning success in previous years, predation, and many other factors. All of them have proven inconsistent at best.
But a new method has surfaced. From the Seattle Times:
"In a paper published this month in the scientific journal PLoS One, researchers reported when they combined 31 indicators ranging from sea surface temperatures to the amount of salmon prey to help predict adult spring Chinook salmon returns to the Columbia last year, the best predictor by far was the presence of food in the ocean.
"Local physical indicators, including water temperature, were not as important.
"A computer model based on the findings has had promising results, accurately predicting 221,000 fish would return in 2011, and nearly nailing the number of fish coming back in 2012, with 180,000 fish predicted, close to the 203,000 that actually came back."
Salmon are eating machines, growing to 20, even 30 pounds in four years where forage is sufficient. They feed constantly. Though, intuitively, it would seem counting the number that smolt and successfully return to sea might provide the best answer, it's hardly surprising to learn that the numbers of salmon returning to our rivers are dependent upon salmon forage counts.
And what are forage counts dependent upon? Just plankton counts, water quality, predation, spawning habitat, fishing harvest (salmon feed primarily on herring, which are severely over harvested for bait, cat food, canned snacks, etc.) — in other words, the overall health of the ocean.
Which, in case you've been in a coma, isn't too good. Dead zones continue growing. New ones keep appearing. Plastics have accumulated in a pile the size of Texas in the Pacific. And fisheries experts the world over report that fish stocks of all kinds are in serious trouble. Many are on the brink of collapse.
And, everywhere, everyone wants to point a finger at someone else. It's the fault of this, or that, the other thing — most commonly the activities of others.
The salmon stocks of the Columbia River have been in trouble for a long, long time. So long that young anglers see these depleted runs as "normal." If their children's children are born after the salmon disappear, will they see a Columbia devoid of salmon as "normal?" The lesson all anglers and all people, young and old alike, should be extracting from the recent discovery that forage is the best indicator of the size of a salmon run: If the forage of the forage of the forage of the forage of the fish you like to catch is in trouble, so is your source of recreation. We can't have great fishing without great habitat. If we're not helping to make that habitat better, we're all part of the problem.
I'm getting reports of Kamloops rainbows, also called "loopers," swarming the river mouths of Lake Superior near Duluth this week. Friends are sending in steelhead reports from all over the country. And, within the next week, we'll be up on the South Shore, looking for steelhead under the ice. Apparently, the size of all those runs could be determined by forage-fish populations in the big lakes.