July 27, 2023 — University of Washington ecologist Daniel Schindler is at the mouth of a salmon stream at Lake Nerka, in Southwest Alaska. It’s roiling with fish.
“They sort of pile up in balls of thousands of fish for a couple of weeks. I think that’s when they’re doing their final maturation,” he said of the sockeye mob. “They’re jostling with each other and splashing, occasionally jumping.”
Schindler is in his 27th year of field work, studying Bristol Bay sockeye. This year is on par with the sockeye abundance Bristol Bay has seen in the last decade, he said, which is far higher than the historical average.
The unlikely hero of this story of plenty: Climate change.
“We tend to think of climate warming is bad news for wild animals,” he said. “But for sockeye Bristol Bay warming has been good news.”
For other salmon, climate change is a villain.
Chinook – or king – salmon are in terrible decline all over the state, and especially dire on the Yukon River. Meanwhile, sockeye – or reds – are having another banner year in Bristol Bay, and everywhere. Scientists say they don’t know exactly why one salmon species is doing so well while the other is in crisis, but some clues are coming into sharper focus.
One key difference, Schindler said, is what kind of river habit each species needs.
Sockeye use lakes as their nurseries. Since the 1980s the water in those lakes has warmed significantly. The warmth stimulates plankton to reproduce more, and young sockeye eat plankton. Fifty years ago, Schindler said, a lot of sockeye spent two years in Lake Nerka before heading out to sea.
“And now they grow so fast that nearly all of them leave after a single year in freshwater, which is a reflection of the fact that the freshwater systems have become more productive,” he said.