Response of euphausiids in the southeastern Bering Sea to variability in environmental factors between a recent cold (2008-2012) and warm (2014-2018) period

• Main Author: Wood, Giulia
• Other Authors: Bernard, Kim, Ciannelli, Lorenzo, Kimmel, David, Oregon State University. Cooperative Institute for Marine Resource Studies, Oregon State University. Honors College
• Format: Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Bering Sea; Kendall; Pacific; Sea ice; Subarctic; Thysanoessa raschii; Thysanoessa inermis
• Online Access: https://ir.library.oregonstate.edu/concern/honors_college_theses/qj72ph168

The southeastern Bering Sea is currently experiencing an oscillation between multi-year warm and cold periods characterized by changes in water temperature, winter sea ice extent, and size of the summer cold pool. Previous studies have observed changes in euphausiid populations in the southeastern Bering Sea between warm and cold periods, but the response of euphausiids to climate variability in the southeastern Bering Sea is not well understood, and previous studies have primarily focused on three dominant species: Thysanoessa inermis, Thysanoessa raschii, and Thysanoessa longipes. In the present study, I examined the response of the dominant subarctic euphausiids, T. inermis, T. raschii, and T. longipes, and two subarctic-transitional species, Thysanoessa spinifera and Euphausia pacifica, to changes in environmental conditions between a recent cold period (2008–2012) and a recent warm period (2014–2018) in the southeastern Bering Sea. Kruskal-Wallis tests were performed to determine changes in mean abundance between the warm and cold periods, and predictors of abundance were assessed with generalized additive models (GAMs). Linear models and Kendall-Theil Sen Siegel nonparametric linear regressions were used to determine if euphausiid populations exhibited latitudinal shifts between warmer and colder conditions. Results showed that T. inermis and T. spinifera were significantly more abundant during the warm period, and T. raschii was significantly more abundant during the cold period. T. longipes and E. pacifica did not show a significant change in abundance between the warm and cold periods. Each species had a specific geographic coverage where abundances were highest. The abundances of T. inermis, T. raschii, and T. longipes were related to sea surface temperature, while the abundances of T. spinifera and E. pacifica were related to the Pacific Decadal Oscillation. The population centers of all species exhibited a general northward trend in response to warmer conditions, but only three out of ten models were ...