Though the Kenai River’s salmon populations are still healthy compared to other Pacific salmon populations, a number of climate change-influenced factors could threaten them in the future.

A study published in the October 2017 issue of the journal Fisheries focuses on the Kenai River as a case study for what may happen to healthy salmon populations as the climate continues to change. Air and water temperatures have been warming over the past 50 years, according to weather records, and other factors in the environment may put stress on salmon throughout their lifecycles as well, the paper’s authors wrote.

The Kenai Peninsula’s economy heavily relies upon salmon abundance for the commercial fishery, sportfisheries and personal-use fisheries. When salmon are more scarce and fisheries managers have to restrict or close sportfisheries, multiple sections of the economy take note — sales tax revenue in the city of Kenai during the personal-use dipnet season may drop, and sales at guided angling services may drop. In the commercial fishery, when the salmon harvest came in significantly below expectations in 2016, reaching only about half the volume of salmon harvested the year before, it pushed total work earnings down on the peninsula, according to the 2017 Situations and Prospects report produced by the Kenai Peninsula Economic Development District.

The authors, who are all from Alaska and include Kenai National Wildlife Refuge supervisory biologist John Morton, detail the potential changes for salmon habitat as well as population trends and implications for management.

Lead author Erik Schoen of the University of Alaska Fairbanks wrote in an email that the researchers wanted to make a broad picture of the available research accessible to the public and to policy makers.

“Alaskans are really interested in fish and wildlife issues, and we’ve been watching all these changes unfold around us,” he wrote. “There has been a ton of great research to document changes on the Kenai, but some of it is only available in technical reports or online databases, and it’s not always easy to see the big picture.”

Major considerations for changing habitat are retreating glaciers, water temperature, increased risk of flooding and additional development and traffic along waterways. Air temperatures on the peninsula have trended warmer in all seasons except fall since the 1960s, according to records from the weather station at the Kenai Municipal Airport, and glaciers attached to the Harding and Sargent icefields — which contribute runoff to the Kenai River — have been retreating and losing mass consistently for the last-half century, with losses accelerating in the past approximately 20 years.

Non-glacial rivers are more subject to temperature fluctuations from warmer air temperatures than glacially fed rivers, according to the study, which drew from stream temperature research by Cook Inletkeeper Science Director Sue Mauger. Some short-term effects may be reduced zooplankton and sockeye salmon production as well as other microorganisms. Other net effects of retreating glaciers on salmon populations aren’t entirely clear and may not all be negative — for instance, additional meltwater flow can moderate water temperatures and add additional connectivity between river channels, according to the study.

“It remains unclear whether glacial mass loss will enhance or reduce the overall salmon productivity of the Gulf of Alaska region,” the study states.

At the same time, pressure on the stream systems has increased with more foot traffic, boat traffic and development within one kilometer of the banks. The population of the peninsula has grown by nearly 10,000 people since 2000, with the greatest density of people in the central peninsula area. Development has also impacted wetlands, which provide nutrients to streams and buffer streamflows by storing extra water and releasing it during dry periods, according to the study.

Human development has increased 20-fold in the Kenai River watershed between the 1980s and 2013, according to the study. More than a third of that development was concentrated in the area within one kilometer of the river between Skilak Lake and Cook Inlet. Human development has led to the introduction of invasive species such as elodea and northern pike that can harm salmon as well, according to the study.

Salmon populations naturally fluctuate over time and depend on a variety of conditions, both freshwater and marine. While some of those conditions are uncontrollable, others are based on management decisions, such as bag limits and fishing seasons. Mixed stocks fisheries like the Kenai can provide a challenge to management as well, leading to complex regulations on both commercial and sportfisheries.

Future conditions may be unpredictable and managers and policymakers should expect them, the authors wrote in the study. Large hatchery releases may threaten wild stocks, both through density reducing oxygen in the water and through competition for food. Managers may also want to consider protecting areas that are not productive salmon habitat now, but could be in the future, such as high glacial streams like the Snow River, the authors wrote. Also, riparian lowlands, which cover much of the western Kenai, appear as a priority, according to the study.

“On the Kenai Peninsula, lowland streams fed by groundwater and wetlands are considered the most vulnerable category of fish habitat, facing threats from a warming climate, invasive species, riparian development, and road crossings lacking adequate fish passage,” the study states.

Fishing-dependent communities like the Kenai may become more resilient to threatened stocks by diversifying their catches, but that could be challenging, especially within a limited entry system, Schoen wrote in an email. The take-home message from the study is that despite the worldwide scale of climate change, local decisions can still have impacts, he wrote.

“Salmon are incredibly adaptable, and they are facing serious challenges and new opportunities all at the same time,” he wrote. “We should expect some surprises in how they respond. Some of the salmon runs that Alaskans have relied on for generations are probably going to decline, but other runs may become more productive, and we have a chance to shape that with strong habitat protections. It’s encouraging to see people working hard to protect habitat on the Kenai and boosting the odds of our salmon runs staying strong.”

Reach Elizabeth Earl at elizabeth.earl@peninsulaclarion.com.