Borealization of nearshore fishes on an interior Arctic shelf over multiple decades

Abstract

Borealization is a type of community reorganization where Arctic specialists are replaced by species with more boreal distributions in response to climatic warming. The process of borealization is often exemplified by the northward range expansions and subsequent proliferation of boreal species on the Pacific and Atlantic inflow Arctic shelves (i.e., Bering/Chukchi and Barents seas, respectively). But the circumpolar nearshore distribution of Arctic-boreal fishes that predates recent warming suggests borealization is possible beyond inflow shelves. To examine this question, we revisited two nearshore lagoons in the eastern Alaska Beaufort Sea (Kaktovik and Jago lagoons, Arctic National Wildlife Refuge, Alaska, USA), a High Arctic interior shelf. We compared summer fish species assemblage, catch rate, and size distribution among three periods that spanned a 30-year record (baseline conditions, 1988-1991; moderate sea ice decline, 2003-2005; rapid sea ice decline, 2017-2019). Fish assemblages differed among periods in both lagoons, consistent with borealization.Among Arctic specialists, a clear decline in fourhorn sculpin (Myoxocephalus quadricornis, Kanayuq in Iñupiaq) occurred in both lagoons with 86%-90% lower catch rates compared with the baseline period. Among the Arctic-boreal species, a dramatic 18to 19-fold increase in saffron cod (Eleginus gracilis, Uugaq) occurred in both lagoons.Fish size (length) distributions demonstrated increases in the proportion of larger fish for most species examined, consistent with increasing survival and addition of ageclasses. These field data illustrate borealization of an Arctic nearshore fish community during a period of rapid warming. Our results agree with predictions that Arctic-boreal fishes (e.g., saffron cod) are well positioned to exploit the changing Arctic ecosystem.Another Arctic-boreal species, Dolly Varden (Salvelinus malma, Iqalukpik), appear to have already responded to warming by shifting from Arctic nearshore to shelf waters. More broadly, our findings suggest that areas of borealization could be widespread in the circumpolar nearshore.

Local environmental conditions structured discrete fish assemblages in Arctic lagoons

“…Thus, landscape features like large Arctic rivers and their nearshore freshwater plumes may represent a dominant structuring force among Arctic estuarine communities that has been maintained during a period of rapid climate change (Rantanen et al 2022). The recently documented community reorganizations, which are primarily driven by sea ice loss and warmer water temperatures (Priest et al 2022;von Biela et al 2023), appear to be nested within the spatial framework that exists along the Beaufort Sea coast.…”

“…The presence or abundance of marine fishes increased in lagoons with greater connection to marine waters, that is when lagoons were more saline-typically later in the summer after the spring freshet or during periods of easterly winds (Craig 1984;Khalsa et al 2021;Priest et al 2022). Marine species can make up large proportions of the fish community's abundance in lagoons, though some species, like polar cod, are episodic in occurrence with their presence linked to strong winds, cold temperatures, and high salinity (Craig et al 1982;Barton et al 2020;von Biela et al 2023). These findings support information generalized from early studies (Craig 1984) and expand on our knowledge of spatial distributions and environmental correlates in Arctic estuarine communities that are experiencing rapid climate change (Meredith et al 2019).…”

“…Among sites near Point Barrow, Alaska, Arctic sand lance CPUE was at least 40 times higher outside of the lagoon compared to capture rates in the lagoon (Barton et al 2020), suggesting capture of this species in lagoons would be rare even using different sampling methods. The absence of polar cod in the lagoons is more likely due to current environmental conditions (i.e., warmer and less sea ice) than from sampling methods, which historically used the same gear and readily captured polar cod when present (Priest et al 2022;von Biela et al 2023). Reduction of polar cod in seabird diets also indicates their decline in nearshore areas as water temperatures increase and summer sea ice declines (Divoky et al 2021).…”

“…For example, in August 2019, offshore sea surface temperatures were < 5 °C (Timmermans and Ladd 2019), while adjacent Alaskan lagoons ranged from 5 to 17 °C (Khalsa et al 2021;Stanek et al 2024). With air and sea surface temperatures increasing over several decades, fish are expected to respond by changing their habitat use and distribution (Ballinger et al 2020;Timmermans and Labe 2020;von Biela et al 2023). Recent investigations suggest that some fish species with boreal zoogeography are becoming more abundant [e.g., saffron cod, uugaq, (common name in English and Iñupiaq, upon introduction) Eleginus gracilis] or changing their seasonal distribution patterns (e.g., Dolly Varden, iqalukpik, Salvelinus malma) in response to warmer temperatures and sea ice extent (Gallagher et al 2021;Priest et al 2022;von Biela et al 2023).…”

“…To improve our understanding, we ask, how do lagoon-specific environmental characteristics (i.e., temperature and salinity) and meteorology (i.e., wind speed and direction) influence fish community composition over 300 km of Alaska's coastline? This question is important because recent changes in fish abundance have a direct effect on the ability of subsistence fishers and marine predators to access desired fish species (Divoky et al 2021;von Biela et al 2023). Further, variation in the physical, chemical, and ecological system can influence the structure of fish communities, which can have profound feedback effects on lagoon food web dynamics and energy flow (Stanek et al 2022a).…”