A Hierarchical Framework to Identify Influences on Pacific Salmon Population Abundance and Structure in the Arctic-Yukon-Kuskokwim Region
Megan V. McPhee, Mara S. Zimmerman, Terry D. Beacham, Brian R. Beckman, Jeffrey B. Olsen, Lisa W. Seeb, and William D. Templin
Abstract.—The causes of spatial and temporal variation in Pacific salmon abundance are poorly understood. An additional challenge in the Arctic-Yukon-Kuskokwim (AYK) region is the expansive and remote nature of salmon habitat. In this paper, the authors discuss a hierarchical framework that may prove helpful in identifying key variables regulating Pacific salmon abundance. The hierarchical framework considers processes that act at multiple scales of space and time, identifies generalizations across scales, and considers interactions among variables operating at different scales. This framework is used to address three overarching questions for the AYK region: 1) What are the important units of focus for conservation and management? 2) What are the factors that control abundance and connectivity of these units? 3) How can these two questions be integrated to better understand and manage Pacific salmon? Genetic and ecotypic units are organized hierarchically in space and time. Genetic units of AYK salmon have been identified at a local level among tributaries in the Yukon and Kuskokwim drainages, the Norton Sound, and at a regional level where all species share similar genetic discontinuities. Ecotypic units are habitat-organismal trait associations characteristic of Pacific salmon, but are not well documented for AYK stocks. The processes controlling abundance and connectivity among these units also occur at multiple hierarchical levels with respect to life history, space, and time. Identifying the scale at which processes or interaction among processes have the largest relative impact on salmon recruitment will be critical to effectively managing Pacific salmon. Four feasible lines of study proposed for gathering informative data from the expansive and remote AYK region include: (1) a spatial comparison between habitat and spawning populations, (2) a comparison of mortality as related to life history diversity, (3) compilation of existing migration data to explain patterns in migration timing, and (4) coordination of genetic data to test hypotheses regarding population structure. Use of existing long-term data and coordination of ongoing research efforts should be of high importance for AYK biologists and managers.