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Studying the harbor seals of Alaska’s Iliamna Lake has proven challenging due to their isolated habitat. They weren’t recognized as a distinct group of harbor seals until 2013. A recent genetic study has uncovered notable differences, suggesting that these seals may represent a unique, native variety of harbor seal. The research indicates that they might be separate in terms of evolution, reproduction, and population dynamics compared to other Pacific harbor seal groups from regions such as Japan, the Commander Islands, additional areas of Alaska, and California.
Only five seal populations exist globally that inhabit freshwater environments throughout the year. The Baikal seal is likely the most recognized, residing in the world’s deepest and oldest lake, located 1,600 kilometers from the sea in Lake Baikal in central Siberia. However, another intriguing group of freshwater seals can be found in Alaska’s Iliamna Lake.
Despite their lesser-known status, the Iliamna seals have long been acknowledged by the Dena’ina Athabascan and Central Yupik peoples of southwestern Alaska, who hold significant cultural and dietary connections to this small species. In contrast to other freshwater seal populations worldwide, seals in Alaska’s largest lake have largely gone unnoticed by scientists. Their remote location and the challenges associated with studying these elusive creatures have contributed to this oversight. It wasn’t until 2013 that genetic studies confirmed their identity as harbor seals.
A lingering question has been whether the seals living in Iliamna Lake are distinct from those in Bristol Bay, the closest marine population. The bay connects to the lake through the 110-kilometer-long Kvichak River. Harbor seals are known to travel over 200 kilometers, and the relatively short distance between the lake and Bristol Bay, along with sporadic sightings of seals in the river, has led to the theory that they may frequently move between freshwater and marine environments.
A research team led by Florida Atlantic University, in collaboration with local indigenous communities, aimed to find out the truth. They conducted a genetic analysis of the seals within the lake and compared them to seals not only from Bristol Bay but from a broad range of the species across the Pacific Ocean, including areas from Japan to California.
The results, published in the journal Biology Letters, indicate that the seals in Iliamna Lake exhibit significant genetic discrepancies from the seals found downstream. These findings suggest they are likely distinct in evolutionary, reproductive, and demographic aspects from other Pacific seal populations, potentially representing a unique native form of harbor seal.
Iliamna Lake seals showed clear genetic differentiation from those sampled at various locations across the Pacific, including Japan, the Commander Islands in Russia, other parts of Alaska, and California. They displayed lower variations in certain genetic markers and somewhat increased estimates of inbreeding compared to marine populations.
“Our findings are both remarkable and unexpected,” expressed Greg O’Corry Crowe, Ph.D., the senior author, program lead, and research professor at FAU Harbor Branch Oceanographic Institute. “Indigenous insights and early accounts by Russian explorers indicate that these seals have been present in Iliamna Lake for at least 200 years. However, it remains uncertain whether this presence is longer or if the differences we observe may indicate that the Iliamna seals represent a unique subspecies, akin to other freshwater seal populations.”
The initial key samples for this study came from subsistence hunters, offering early evidence that movements of seals between Iliamna Lake and Bristol Bay might be limited. However, the small number of samples made it necessary to interpret these initial results cautiously. With few options for additional samples, research efforts reached an impasse.
Momentum picked up when a team from the University of Washington, including co-author Donna Hauser, Ph.D., now a research associate professor at the University of Alaska Fairbanks, International Arctic Research Center, collected seal scat (feces) samples from various locations around Iliamna Lake. They worked in collaboration with co-author Thomas P. Quinn, Ph.D., a professor in the School of Aquatic and Fishery Sciences at the University of Washington. This new series of samples provided an opportunity for heightened genetic analysis and revitalized the research.
Partnering with scientists from the National Oceanic and Atmospheric Administration (NOAA), the FAU team analyzed hundreds of scat samples. While collecting sufficient DNA proved to be challenging, resulting in many samples being unusable, the scat analysis significantly increased the sample size and provided the statistical power required for a more thorough examination.
“It can be disheartening to discard samples that don’t meet genetic screening standards, especially after dedicating so much effort and time,” remarked Tatiana Ferrer, the first author and coordinator of research programs in the FAU Harbor Branch Wildlife and Behavior program. “Despite the frustrations and long hours in the lab, the ultimate success and invaluable data make it all worthwhile. Our hard work yields meaningful results.”
The FAU team and NOAA are planning further studies on the Iliamna seals, which will include additional sampling and genomic analyses. This will help clarify their relationships with other seal populations and provide insights into how genetic diversity is generated, maintained, or lost in small, isolated populations, as well as how species that typically reside in marine habitats adapt to freshwater settings.
“We can now confidently state there exists a distinct population of seals in the lake that receives no or very few new individuals from the much larger nearby marine harbor seal populations,” noted Peter Boveng, co-author and research analyst at NOAA’s Alaska Fisheries Science Center. “I am highly optimistic about upcoming studies that will explore whether the lake seals differ significantly from their marine relatives in areas like ecology and evolution.”
Recently, there has been growing concern for Iliamna Lake and its ecosystem, especially with increasing interest in mineral exploration and development in the area.
“My interest in Iliamna seals started during my undergraduate years at the University of Washington, which led to my first research project on their feeding habits and behavior. This work, published in 2008, was the only study on them for many years,” shared Hauser. “When I returned to Iliamna Lake in 2015 and 2017 with my family, I saw a chance to gather valuable samples from this unique seal population. I hope this research encourages further studies and collaborations with local communities and holders of Indigenous Knowledge.”
Comprehensive scientific data are essential for effective species management and conservation. The authors hope that the insights gained from this study will aid in the collaborative management of seals and assist NOAA, the federal body responsible for harbor seal management in Alaska, in its decision-making processes.
“I have been intrigued by these seals since I began my work on Iliamna Lake back in 1987, but real progress didn’t occur until Donna Hauser’s dietary study over two decades ago,” stated Quinn. “Witnessing these impressive genetic findings and the expanding research connection to the local community is truly wonderful. I am optimistic that more discoveries regarding the physiology and behavior of the seals, along with their evolution, are on the horizon.”
Other authors of the study include David Withrow, a former research scientist at NOAA’s Alaska Fisheries Science Center, and Vladimir Burkanov, Ph.D., chief scientist at North Pacific Wildlife Consulting.
“This study has significantly advanced our understanding of these seals; however, further research is essential as it has unveiled a whole new set of questions. That is simply the nature of science,” O’Corry-Crowe reflected. “We aim to collaborate with the Iliamna and Bristol Bay communities to continue addressing their queries, gain knowledge about these remarkable animals, and contribute to ensuring the future of the Iliamna Lake seal.”
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