Multidecadal Trends in Body Size of Puget Sound Chinook Salmon: Analysis of Data from the Tengu Derby, a Culturally Unique Fishery

Abstract

In Pacific salmon Oncorhynchus spp., downward trends in size and abundance have been reported for species and stocks for over 40 years, but the patterns are inconsistent among regions and species. Interpretation of these trends is complicated by many possible contributing factors, including short time series, data comprising a mix of stocks, and varying gear types. Here, we present data on the mass of individual Chinook Salmon Oncorhynchus tshawytscha caught in the winter from 1946 to 2019 in central Puget Sound, Washington, by participants in what may be the longest running Pacific salmon derby in North America, the Tengu Derby. In this annual recreational fishing competition, established by Japanese Americans immediately after release from internment camps at the end of World War II, participants follow strict gear, area, and methods regulations and catch almost exclusively salmonids originating from and remaining in Puget Sound. Records revealed an overall decline in fish mass over the decades, with a high degree of variability throughout the time series. Specifically, resident Chinook Salmon exhibited several shifts, including a decrease in size from a high in the 1950s to a low around 1980, followed by an increase to another high around 1990 and then a decline over the most recent 30 years. These size trends of residents differed from those of Puget Sound Chinook Salmon as a whole. We infer that the resident fish experienced ecological conditions affecting their growth that were distinct from those of fish feeding along the Pacific Ocean in the same periods. These distinct trends in size of Chinook Salmon from common origins indicate that the different migration patterns of fish within stocks must be considered in the analysis and interpretation of body size trends and also in patterns of survival.Long-term trends in size and age at maturity of fishes have been the subject of interest for many decades as they may reflect natural changes in environmental conditions (Cox and Hinch 1997; Rogers et al. 2011), density dependence (Millner andWhiting 1996;Pyper and Peterman 1999), fishery management (Richards and Rago 1999), fishery-induced evolution (Swain et al. 2007;Sharpe and

Body length changes for Atlantic salmon (Salmo salar) over five decades exhibit weak spatial synchrony over a broad latitudinal gradient

“…It is common for the strength of spatial synchrony to decrease with distance or geographic barriers (Liebhold et al., 2004 ; Walter et al., 2017 ). In Eastern Canada, it is possible that conditions experienced during migration from rivers to common feeding areas act as a desynchronizing factor (Quinn et al., 2022 ). For example, southern rivers have the longest migrations as they travel through the Bay of Fundy, Gulf of Maine and/or Atlantic Ocean to reach feeding areas, whereas mid‐latitude populations from the Gulf of St. Lawrence migrate northward through the Strait of Belle Isle (between Newfoundland and Quebec), and northern populations essentially enter the feeding area directly after leaving their rivers (Bradbury et al., 2021 ; Chaput et al., 2019 ; Lacroix, 2013 ).…”

“…In Eastern Canada, it is possible that conditions experienced during migration from rivers to common feeding areas act as a desynchronizing factor (Quinn et al, 2022). For example, southern rivers have the longest migrations as they travel through the Bay of Fundy, Gulf of Maine and/or Atlantic Ocean to reach feeding areas, whereas mid-latitude populations from the Gulf of St.…”

Productivity and resilience of Chinook salmon compromised by ‘Mixed-Maturation’ fisheries in marine waters

“…Such observations in Chinook salmon (O. tshawytscha) have been documented since the 1920s. Chinook salmon have displayed marked declines in size-at-age and declines in the proportion of older, larger individuals, particularly females, in many populations across their range in the eastern Pacific and watersheds from the Pacific Northwest to Alaska [1][2][3][4][5][6][7][8][9][10][11][12].…”