Salmon are one of the most iconic fish species in the world, known for their remarkable ability to return to their natal rivers to spawn after spending years in the ocean.
However, not all salmon follow this pattern. Some of them stray to new habitats, especially when their original ones are changing due to climate change.
This is what researchers from the University of Alaska Fairbanks (UAF) have confirmed in a recent study: salmon are spawning in Arctic rivers that flow into the Arctic Ocean, a region that was previously too cold and inhospitable for them.
How did the researchers find out?
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The researchers were interested in exploring the possibility of salmon colonization in the Arctic Ocean watershed, which covers about 40% of Alaska's land area.
They were motivated by a workshop held in December 2022, where scientists, community members, and Indigenous fishermen discussed the increasing number of salmon being observed in the Arctic Ocean and their possible origin.
The researchers focused on the Colville River watershed, which is approximately 60 miles southwest of Prudhoe Bay.
The Colville River is the largest river that drains into the Arctic Ocean from Alaska. The researchers sampled two of its tributaries: the Anaktuvuk and Itkillik rivers, which are located in the Brooks Range mountains.
The researchers used a combination of methods to survey the rivers, including electrofishing, gillnetting, snorkeling, and environmental DNA (eDNA) sampling. They also collected water temperature, dissolved oxygen, conductivity, and pH data.
The study found about 100 chum salmon in the Anaktuvuk and Itkillik rivers in mid-September 2023.
All the fish were either actively spawning or had finished spawning at sites where groundwater appeared to be flowing to the surface.
These sites had warmer and more stable water temperatures than the surrounding areas, which are essential for salmon reproduction.
Chum salmon eDNA has also been detected in both rivers and pink salmon in the Anaktuvuk River.
eDNA is the genetic material that organisms leave behind in their environment, such as skin cells, scales, or feces. It can be used to identify the presence and diversity of aquatic species without capturing or observing them directly.
The researchers confirmed that these salmon were not escapees from hatcheries or aquaculture facilities, as they had no external marks or tags.
They also ruled out the possibility that these salmon were transported by humans or animals, as there were no roads or trails near the sampling sites.
The Arctic is warming faster than any other region on Earth, which affects the hydrology, ecology, and biogeochemistry of its rivers and lakes.
Some of these changes could create more favorable conditions for salmon colonization, such as longer ice-free seasons, higher water temperatures, increased nutrient availability, and reduced salinity.
However, not all changes are beneficial for salmon. Some of them could pose challenges or threats, such as increased variability and unpredictability of water flows, lower dissolved oxygen levels, higher acidity and turbidity, increased competition and predation from native and invasive species, and exposure to contaminants and pathogens.
The researchers emphasized that these salmon are not necessarily permanent residents of the Arctic rivers.
They could be transient visitors that will not establish self-sustaining populations. They could also be indicators of ecological stress or disturbance in their original habitats.
The researchers called for more studies to monitor and understand the dynamics and impacts of salmon colonization in the Arctic.
They acknowledged that these salmon are not new to the Arctic people who have lived there for thousands of years.
According to them, indigenous knowledge and observations are valuable sources of information for studying salmon distribution and abundance in the Arctic.
They hoped that their findings could contribute to a collaborative dialogue between scientists and communities on how to manage and conserve salmon resources in a changing Arctic.
