Population Trends for Chinook and Summer Chum Salmon in Two Yukon River Tributaries in Alaska

Abstract

An essential management objective of the Yukon Delta and Koyukuk National Wildlife Refuges in Alaska is to conserve fish and wildlife populations and habitats in their natural diversity. In keeping with this objective, the U.S. Fish and Wildlife Service installed weirs in two tributaries of the Yukon River, the East Fork Andreafsky and Gisasa rivers, in 1994 to collect information on salmon populations that used them. The weirs have been in operation for >23 y. Chinook Oncorhynchus tshawytscha and summer Chum Salmon O. keta were counted and sampled for various demographic data each year as they migrated through the weirs to upstream spawning areas. Here we examine this record of population data to describe and compare long-term variation in run abundance, run timing, length and age structure, sex composition, and production for these salmon populations. Fishery managers often look to multiple monitoring projects in-season seeking corroboration of observed run qualities; therefore, we also considered whether Yukon River main-stem indicators of abundance were correlated with these tributary escapements. Our analyses suggest long-term stability of these populations despite large annual variations in most metrics we examined. Annual escapements have varied by factors of 3–5 for Chinook Salmon and >23 for summer Chum Salmon, yet only the Chinook Salmon population in the Gisasa River appears to be declining. Main-stem abundance indicators were not correlated with Chinook Salmon escapements but were strongly correlated with summer Chum Salmon escapements. Run timing has varied annually by as much as a week earlier or later than average for all four populations with no trend over time. Mean age of the Chinook Salmon populations declined over time but remained stable for the summer Chum Salmon populations. Chinook Salmon populations in the East Fork Andreafsky and Gisasa rivers averaged 35% and 28% female, respectively. Both summer Chum Salmon populations averaged close to 50% female. Length at age has been stable or slightly declining for all four populations. Production over time was strongly correlated within species for populations in the two rivers, and averaged >1 recruit/spawner for all populations except Chinook Salmon from the Gisasa River. We discuss these findings in the context of major changes in the fishery and the environments these populations experience.

Heterogeneous genetic basis of age at maturity in salmonid fishes

“…First, variation in breeding age buffers populations from diversity loss following catastrophic environmental events via the "portfolio effect" (Greene et al, 2010;Satterthwaite et al, 2017;Schindler et al, 2010). Second, such lifehistory variation reduces interannual variability in adult returns and the frequency of fishery closures, which benefits commercial, recreational, and subsistence fisheries and associated communities (Brown & Godduhn, 2015;Copeland et al, 2017;Greene et al, 2010;Schindler et al, 2010). Third, as age at maturity is positively correlated with size and larger individuals may be preferentially targeted by fisheries, fisheries induced evolution can result in reductions in population variation and therefore viability.…”

Development of a Simple Morphometric Model to Identify Sex in Chinook Salmon Returning to Spawn in the Yukon River

“…State and Federal agencies in Alaska generally measure only MEF length of Chinook Salmon (Lozori and McIntosh 2014;McDougal and Lozori 2017;Brown et al 2020). The field application of this quantitative method when handling live fish struggling to escape must be simple and brief.…”

“…However, both require significant time and equipment to perform and generally require that the fish be anesthetized as well. It would be challenging to adapt these methodologies to typical field sampling conditions in the Yukon River such as boat-based drift netting programs (Lozori and McIntosh 2014;McDougal and Lozori 2017) or weir-based programs in remote tributary streams (Brown et al 2020).…”

A New Genotyping‐in‐Thousands‐by‐Sequencing Single Nucleotide Polymorphism Panel for Mixed‐Stock Analysis of Chum Salmon from Coastal Western Alaska

“…2009; Menard 2016; Brown et al. 2020). In 2021, the Yukon River summer Chum Salmon run was disastrously low, prompting concerns over food security, income, and the sustainability of Yukon River salmonid populations, particularly as the failure of the Chum Salmon return came on top of ongoing shortages of Chinook Salmon O. tshawytscha in the region (R. Alstrom, Yukon Delta Fisheries Development Association, personal communication).…”

“…Chum Salmon populations in western Alaska plummeted in the period between 1997 and 2002, prompting multiple fisheries disaster declarations (Menard et al 2009). In the early 2000s, some stocks rebounded, while others failed to meet their escapement goals (Linderman and Bergstrom 2009;Menard et al 2009;Menard 2016;Brown et al 2020). In 2021, the Yukon River summer Chum Salmon run was disastrously low, prompting concerns over food security, income, and the sustainability of Yukon River salmonid populations, particularly as the failure of the Chum Salmon return came on top of ongoing shortages of Chinook Salmon O. tshawytscha in the region (R. Alstrom, Yukon Delta Fisheries Development Association, personal communication).…”