Fly Fishing Insider Podcast
Overfishing is the smallest of salmon's problems. Most Atlantic commercial salmon fisheries are already closed and returns keep declining, which points at riverbank destruction, dams, deforestation, agriculture, pollution and climate change instead. Salmon live in both fresh and salt water, so they absorb nearly every mistake humans make on the planet.
Mark Kurlansky is the author of Salmon, published by Patagonia, along with more than thirty other books including one on the Atlantic cod fishery.
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Why is overfishing not the main threat to salmon?
A fishery whose only problem is overfishing has a relatively simple problem. Most Atlantic commercial salmon fisheries have been closed and salmon returns are still falling, which rules overfishing out as the driver. The remaining causes are riverbank destruction, dams, deforestation, poor agricultural practice, pollution and climate change. Salmon were chosen as the subject precisely because a fish that lives in fresh water and ocean water gets hit by all of it.
How does carbon dioxide in the ocean affect salmon?
Roughly a third of the carbon dioxide produced on land ends up in the ocean, which changes the ocean's chemistry. Zooplankton and the other base organisms grow far less than they used to, so there is less food for large fish including salmon and cod. River managers around the Atlantic reported good spawning and healthy outbound populations, then saw the fish not come back. The mechanism is starvation at sea rather than a failure in the river.
How does water temperature limit salmon?
Salmon cannot live in water warmer than 68 degrees Fahrenheit, which puts a hard ceiling on where they can survive. Warm summers in Alaska have cut runs down even in years when the runs themselves were good. That temperature limit is one of the clearest ways climate change reaches salmon directly rather than through the food chain.
Why do most salmon hatcheries fail?
Hatcheries have failed for centuries because they were built without understanding how adaptable salmon are. Two sockeye in adjacent rivers carry completely different DNA; salmon in one river are strong leapers, in the next they are built for wide bends. They are effectively reinvented for each river. Producing generic salmon in a hatchery and dropping them into a river ignores that, and hatchery fish arrive without the survival skills wild fish have.
When does a hatchery actually help a river?
A hatchery works as a one-time restoration tool, not an ongoing supply. In Maine and on the Elwha, wild fish returned after dam removal but not fast enough, and hatchery fish were used to build the population. The clearest case involved a Scottish river bought cheaply because its salmon were extinct: the new owner used a hatchery to seed the river once, then let that population reproduce on its own, and it is now considered a good salmon river. Repeated stocking restarts the clock each time.
Why did damming rivers look like a success story?
The industrial revolution used water power to drive mills, and the mills then dumped pollution back into the same water, so damming and pollution killed British rivers together. New England repeated the pattern to build a mill economy, and New Englanders carried it to the Pacific Northwest, where rivers like the Columbia were far more powerful than eastern rivers. The Pacific Northwest became a major electricity producer and built an economy on it. Nobody learned from the earlier failures because each round was judged a success.
What is fly fishing in Kamchatka like?
Reaching the camps means a flight to Russia, a long trip from the nearest town and then an aging Soviet troop-transport helicopter. Kamchatka holds salmon-sized rainbow trout alongside chinook, sockeye, chum, char and grayling, and a typical day can produce five or six species, with the fight sometimes the first clue as to what is on the line. Insect density is extreme enough to force fishing from a boat in the middle of the river and casting back toward the buggy banks where the fish are.
Key takeaways
- Closing commercial fisheries has not reversed Atlantic salmon decline, which means overfishing was never the primary cause.
- About a third of land-produced carbon dioxide enters the ocean, cutting plankton growth and starving large fish.
- Salmon cannot survive in water above 68 degrees Fahrenheit, so warm summers shorten runs even in strong years.
- Salmon DNA differs river to river, which is why generic hatchery stock rarely establishes.
- Hatcheries can work as a single seeding event followed by natural reproduction, not as continuous stocking.
- Preserve riverbanks and avoid building on them; wading rather than tramping the bank is part of that.
