Coho salmon fry at its early stages of development.
Seymour Salmonid Society
In a transformation that has happened for thousands of years, once the outer layer of its egg is breached, the creature - known as an alevin - will begin growing into a coho salmon.
Last fall, a female salmon carefully chose a location to deposit eggs to minimize predation, enhance development and maximize survival during this sensitive stage, yet little is known about how locations are chosen and passed through generations.
The eggs developed slowly in optimal stream conditions over several months. Each egg’s chances of survival are already extremely low, but if stream conditions change during egg development, its prospects dim even more.
The tiny alevin is almost impossible to see in the stream, but it looks something like a bloated tadpole with a huge yolk sack attached to its skinny body. Over the next several weeks, it will absorb the nutrient-filled yolk sack as it sneaks between rocks in the stream to elude predators.
Photo: Coho salmon fry are able to drastically consume more resources once they reach 70mm. By Seymour Salmonid Society.
Soon the alevin will develop into a fry, and when it reaches a critical size of about 70mm, will it be able to consume unhatched salmon eggs from the bottom of the stream. Until then, it will focus mainly on staying alive and consuming macroinvertebrates that drift in the stream.
Once young fish are strong enough to move efficiently in the current, their food options grow and many begin to relocate throughout the stream and its watershed to feed and grow before they begin their transformational journey as smolt to sea.
Three years ago, The Wilderness Society’s research team in the Alaska office set out to tackle the difficult task of understanding how climate change might affect freshwater streams and the coho salmon populations in Alaska’s Chuitna watershed by the end of this century. Predicting the effects on salmon is particularly complicated because of their long migrations and the varying amounts of time they spend in a range of marine and freshwater habitat over the course of their lives.
Photo: The outlet of the main stem of the Chuitna River drains into western side of Cook Inlet near the community of Beluga. Its clear water provides ideal habitat for coho salmon. By Jason Leppi.
One of our first steps was to create computer model to simulate the local hydrology within the Chuitna. Next, we developed a salmon model to simulate survival rates and track generations of salmon throughout the portions of their lives spent in the freshwater stream. We then linked our models with predicted future climate data to simulate stream conditions and salmon populations in the years 2080-2100.
Our results show that climate changes could have mixed effects for salmon, depending how much air temperature and precipitation increase in a given year. If the climate warms a lot, with a minimal increase in precipitation, then salmon productivity will likely increase, thanks to warmer, more suitable stream conditions in the Chuitna.
But if the climate only warms a little, with a large increase in precipitation, salmon productivity will likely decrease because winter floods will scour salmon eggs from the bottom of the stream.
We also found that a rise or fall in salmon production was dependent on localized changes in hydrology within specific subwatersheds. This research highlights the complexity of predicting climate change-related effects on salmon populations, and demonstrates that population effects will depend on the severity of climate change effects in local areas, as well as the characteristics of each area’s streams.
Photo: Lone Creek (a tributary to the Chuitna watershed) provides a diversity of habitat for various life stages of coho salmon. By Jason Leppi.
This is important for future management of salmon streams in Alaska because we are likely to see salmon production falling significantly in some areas, while it will probably increase in others.
If we want to have sustainable fisheries in the future, we will need to protect the biodiversity of our salmon populations. To do that, we must protect a wide array of habitats to ensure that if productivity drops in some streams, we will have other watersheds with suitable habitat where populations can increase.
Like other species, salmon in Alaska will likely respond in both negative and positive ways to the changes we have caused in the world’s climate. Permanently protecting large, wild interconnected landscapes will provide salmon the necessary capacity to adapt, and will be critically important for the vitality of future salmon populations in Alaska.
For more information on methods and results please see the author’s recent paper in Global Change Biology.