(CN) — Folks in Alaska have noticed for years that Alaskan wild salmon, one of the most important creatures to Alaska’s economic and environmental wellbeing, have slowly been getting smaller and smaller – and now researchers have begun to understand why.
In a state often dominated by wildlife management, commercial fishing opportunities and ocean-to-land resource distribution, few things influence the state of Alaska as much as wild salmon. They help to support local fisheries, provide needed nutrition for Alaskan people and animals alike and help to fertilize the ecosystems and rivers that make up their natural spawning grounds.
Given the critical and numerous roles that wild salmon play for the people and environment of Alaska, it is understandable why many in Alaska became concerned when they began to notice an unwelcome phenomenon; when salmon returned to their spawning grounds after migration, the returning fish seemed to be getting smaller. These smaller salmon potentially represent worrisome consequences for Alaska, given that smaller salmon means smaller meals for subsistence fishers, smaller profits for commercial fishers and fewer crucial nutrients for local ecosystems.
While it has been no secret that wild Alaskan salmon have been gradually diminishing in sizes throughout the years, it has been unclear on what exactly is causing the shrinkage — but researchers say they just may have cracked it.
According to a study published Wednesday in Nature Communications, researchers from the University of California, Santa Cruz and the University of Alaska Fairbanks compiled fish-related data from the Alaska Department of Fish and Game that dates all the way back to 1957. This massive collection of data gave researchers insight into nearly 12.5 million fish comprised of four distinct salmon groups — Chinook, chum, Coho, and sockeye — so that they could better understand the growth patterns and trends Alaskan salmon have experienced in the last several decades.
After poring through this data, researchers determined that the primary cause behind decreased fish size is that they are simply not spending enough time at sea before returning to their spawning grounds. Despite being able to spend up to seven years at sea, time spent growing and feeding into maturity, many salmon are making the trek back to their river spawning homes far earlier than they used to.
"There are two ways they could be getting smaller — they could be growing less and be the same age but smaller, or they could be younger — and we saw a strong and consistent pattern that the salmon are returning to the rivers younger than they did historically,” said Eric Palkovacs, corresponding author of the study, professor of ecology and evolutionary biology and associate director of the Fisheries Collaborative Program in the Institute of Marine Sciences at UC Santa Cruz.
What is actually causing fish to spend such less time at sea, however, is a more complicated question. Researchers suggest that there are likely several factors that have combined to influence these migration patterns for Alaskan salmon, and that there is no one single culprit to blame.
Two widespread factors that have likely influenced most groups of salmon are climate change and competition related to the growing numbers of wild and hatchery salmon in the ocean. As habitat conditions and salmon populations change over time, researchers say that such changes are bound to have an influence on how long fish elect to stay at sea.
Commercial fishing ventures also likely play some part in this equation, but researchers say that this likely only influences certain groups of salmon in select geographical areas.
Researchers also suggest that the ocean is simply becoming too dangerous a place to be for many salmon. While staying in the ocean for a longer period of time does result in salmon becoming stronger, larger and healthier, every year spent at sea is a gamble for salmon due to the threat of potentially never surviving long enough to return home to spawn. Some salmon, therefore, decide to the take the less risky route and return home early when they are still young.
"Natural selection has always pushed in both directions, but the balance between the two is changing, pushing harder against the older, larger salmon," Palkovacs said. "It seems that the ocean is becoming a riskier place to be."
Researchers say that with the potential dangers that these younger, smaller salmon can bring about for Alaska and its people, Alaskan management agencies and fisheries need to become aware of more than just the number of salmon entering their freshwater and start looking deeper into the problem.
“Alaska salmon have long been managed for sustainable harvest. However, our work shows that not only the number of salmon, but also their individual characteristics have important implications for the services salmon provide to ecosystems and people,” said Palkovacs. “In addition to considering the number of salmon caught in fisheries and returning to freshwater each year, management should consider the traits of individual fish, chief among them — size and age.”
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