What climate change and extreme temperatures could mean for Bristol Bay salmon
Bristol Bay sockeye populations are booming, but what is the tipping point?
This summer is a colder, rainier, and buggier season in Bristol Bay, and across Alaska. Meanwhile, last week the world faced four straight days of the hottest temperatures on record, marking Earth’s extreme warming.
The biggest challenge of climate change for Bristol Bay salmon isn’t necessarily warming temperatures right now. It is the variability, said Bill Templin, Chief Salmon Fisheries Scientist for Alaska Department of Fish and Game.
"You know, climate change isn't just directional. It's not just that things are warming, it's also that there's greater variability in the systems," he said.
Templin believes these cold, wet, stormy summers are a product of climate change too.
"There can be a wider swing of hot and cold or dryness, drought, flooding, excessive water in the systems," said Templin. "That variability makes it hard for an organism to adapt to the changes which can lead to reduced productivity from systems that are otherwise healthy, with healthy habitats and low fishing pressures."
What does that mean for salmon?
There’s some good news. Starting in freshwater, where salmon return to spawn and remain the first year of life, Bristol Bay’s deep lakes provide a natural buffer to temperature changes.
"So it seems like the lakes are really this big buffering mechanism," said fisheries ecologist and researcher Daniel Schindler with the University of Washington’s Alaska Salmon Program. That’s critical for the salmon’s success.
Freshwater lakes are deep and stratified, meaning temperatures of the water are warmer at the surface going down to cooler at the bottom. Salmon can dive deep and escape warmer surface temperatures. According to Schindler, that means they can return to spawn earlier if ocean temperatures are too warm, like the birth ward at the hospital.
“That allows them to adjust when they migrate in from the ocean, and basically chill out until it's time to spawn, which is much later in the season for fish that spawn in warm sites within watersheds,” he said.
In other words, the lakes and rivers above Bristol Bay can withstand a bit of temperature change. Salmon can’t regulate their own heat but they are very good at adjusting their depth to find the most comfortable water temperature.
Bristol Bay’s spawning grounds are also seeing a boom in what sockeye are eating - zooplankton.
Schindler believes it may be the "goldilocks zone" of favorable conditions for sockeye right now. He said the things that salmon eat love that warmer top layer of lakes in Bristol Bay. That means more food for juvenile sockeye, which means salmon leaving for the ocean as big, well-fed fish, which means relatively high survival rates on average.
"So if we look where this might be going over the next 20 years, I think it's safe to say that the lakes probably are not going to get any colder. Our best estimate is that the productivity of the lakes will continue to increase. This probably won't translate into any differences in runtime, that's really most likely affected by conditions they encounter at sea, not conditions they encounter in the lakes," said Schindler.
That buffer for spawning salmon can only go so far though. What happens when climate change alters water temperature past that “goldilocks zone”? Schindler suggested we should expect to see changes in the behavior of sockeye.
"Over the long term, with more climate change and more adaptation, we might see changes in spawn and run timing," he said.
There’s a sci-fi movie trope where someone goes back in time and accidentally does something miniscule that alters the course of space time in an unforeseeable way. In a way, the cascading and unpredictable effects of climate change in southwest Alaska could be like that. Our ecosystems are unimaginably complex and researchers don’t know what will happen when one factor is tweaked. A snow cap can prematurely melt miles away and flood the watershed, a lake can get a little warmer and suddenly entire industries have to adapt.
For the Bristol Bay sockeye fishery estimated at more than $2 billion, that butterfly effect of climate change could have massive impacts for fishermen and the communities dependent on the fishery.
Bill Templin said most likely, those climate change effects could be seen in the open ocean where sockeye spend most of their life.
"So, we would expect water temperatures in the ocean to have a bigger effect on their size, their survival, and the age that they return," Templin explains, "because the ocean is a very productive place, and they do most of their growing there. So we would expect temperatures in the ocean to potentially have a bigger effect than freshwater temperatures."
Of course, there is no open-shut case. Templin referenced recent research from the University of Alaska which shows that different species of salmon are associated with different temperatures and locations at sea. This may provide part of the reason why some salmon species are booming while others, like chinook, are under threat. As sockeye are pushed to the top of that climate bubble, other species that respond less favorably to warmer sea surface temperatures begin to tip over the edge.
But what is that tipping point for Bristol Bay sockeye?
Templin believes we have to go back to the lakes to understand what a tipping point may look like.
"Tipping points have been seen in other systems, maybe not the way that we often think of them. But kind of a point where - not a point of no return, so to speak - but where systems flip into a new mode."
Templin used this example: "You notice how the top foot or two of water is a lot warmer? And when you dive down and get into some really cold water? That stratification of the lake water can be disturbed by a lot. When they get a big windy event and it mixes the water, that changes the way the ecosystem acts. So there's a tipping point in many lakes. There's a time during the year when enough of the sun and the wind has stirred it up enough that that stratification breaks down. And the water column becomes more uniform in its temperature."
When that buffering system in the lakes breaks down, Templin said, so does the ecosystem. Glacial melt, cold water inputs, algae, silt, these are all factors that could contribute to a potential tipping point, the straw that breaks stratifications back.
Templin assured it's not all doom and gloom yet, the tipping point won’t be tomorrow. Bristol Bay rivers are short and cold and the lakes are hardy.
"But the lakes do provide a lot of buffer. They form kind of these cold water reservoirs, as well as the ability for lots of fish to to survive, thrive and grow juvenile salmon within these lakes," he said.
When asked if the Alaska Department of Fish and Game is keeping an eye on climate change and the future volatility of Bristol Bay watersheds, Templin said the department is more focused on management.
"The department is not necessarily a research organization like a university. Our responsibility is to manage and to manage for the benefit of the people in the state and the sustainability of the systems. So most of our research has to do with improving management and understanding the species."
Alaska fisheries managers are tasked with managing the fast-paced, dynamic Bristol Bay runs each year, and that will also mean adapting to climate changes in the future. The only thing we know for sure is that tomorrow, for better or worse, whether a fisher or a fish, Bristol Bay industries and ecosystems must adapt together.