The decline in abundance and body length of Chum Salmon in the Fishing Branch River, Yukon

Numerous populations of Pacific salmon have experienced decreased abundance and body size in the past 50 years. Ni’iinlii Njik (Fishing Branch River) in northern Yukon is the natal stream to the largest population of Chum Salmon Oncorhynchus keta in northern Canada. For over 50 years, total spawner abundance, age, sex and fork length data were collected from thousands of spawning Chum Salmon. We asked whether there were systematic changes in the body length, age, and sex ratio of spawning Chum Salmon from this population over this time frame. Age, sex, and fork length were sampled from 23,906 spawning Chum Salmon, and total spawner abundance was counted over 50 years (1972–2022) from the Fishing Branch River, a tributary of the Yukon River and natal stream to the largest Chum Salmon population in northern Canada. Total spawner abundance has decreased significantly since the 1970s, and the average fork length of females and males declined 3.1% and 3.6%, respectively. This statistically significant decline in average length was associated with significant reductions in length at age of 4- and 5-year-old fish. Age-3 females and 6-year-old fish did not have significant declines, though they are much smaller components of the age structure. There is some indication that Chum Salmon are also maturing to spawn at earlier ages in this population, with age-4 fish increasing in relative abundance. The average age of spawners decreased from 4.6 to 4.3 years for male fish and from 4.5 to 4.2 years for female fish. These declines parallel other documented declines in body length and age of salmon in the North Pacific Ocean. Causes for body size and abundance declines may include changing marine conditions and increased competition from hatchery and wild Pink Salmon Oncorhynchus gorbuscha and Chum Salmon across the North Pacific Ocean. Decreased body length translates into lower per-capita reproductive output, and management strategies that do not incorporate these shifting demographic characteristics may have detrimental consequences on future abundance and productivity of Chum Salmon in this and other ecosystems.

• Publication year

  2025

• Venue

  Transactions of the American Fisheries Society

• Publication date

  2025-04-10

• Fields of study

  Not labeled

• Identifiers
  DOI 10.1093/tafafs/vnaf005
• External record

  Open on Semantic Scholar

• Source metadata

  Semantic Scholar

• No claims are published for this paper.

• No concepts are published for this paper.

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