Size and timing of hatchery releases influence juvenile-to-adult survival rates of British Columbia Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon

Abstract

Salmon hatcheries are management tools intended to stabilize declining abundance in salmon populations and sustain salmon fisheries. One key area of uncertainty is how hatchery release practices influence juvenile-to-adult survival. Data quality and quantity vary considerably among hatcheries making it difficult to assess the role of release practices. Using a Bayesian hierarchical approach, we analyzed releases and recoveries of Chinook ( Oncorhynchus tshawytscha; 21 hatcheries) and coho ( Oncorhynchus kisutch; 16 hatcheries) salmon in British Columbia from 1972 to 2017. Higher survival rates were associated with increasing weights-at-release, earlier releases of Chinook salmon, and later releases of coho salmon. The addition of environmental (sea surface temperature, Pacific Decadal Oscillation), and predator (harbour seals, killer whales) covariates did not improve model performance relative to models that used year effects to account for declines in survival and interannual variability in ocean conditions. Optimizing release practices could increase returns by 6%–245% for Chinook salmon and 5%–160% for coho salmon based on median posterior estimates for each hatchery. With these results, a large-scale adaptive management approach could be implemented to test our understanding of release practice–survival relationships and evaluate cost–benefit trade-offs.

Acoustic telemetry tracking of Coho Salmon smolts released from a community‐run hatchery into a marine inlet reveals low early ocean survival

“…Aquatic predators such as Pacific Spiny Dogfish Squalus suckleyi and harbor seals Phoca vitulina, which are also common in our study area, may be a source of mortality for out-migrating Coho Salmon smolts as they are in other systems and for other salmon populations (Beamish et al 1992;Berejikian et al 2016;Thomas et al 2017;Allegue et al 2020). The abundance of such predators during smolt migrations has been found to have significant negative effects on juvenile-to-adult survival for some hatchery populations of Chinook and Coho salmons in British Columbia (James et al 2023). Furthermore, the "dead end" of Burrard Inlet, where smolts are released (i.e., Port Moody Arm), and the spatial constrictions that are characteristic of the inlet (e.g., at Caraholly Point) may create a "predator pit," where predators aggregate and consume migrant smolts in high numbers (Zimmerman and Ward 1999;Petersen 2001).…”

“…These facilities regularly assess the effectiveness of their operations through large-scale programs that monitor return survival using coded-wire tags, adipose fin clips, genetic tagging, and thermal marking (Fisheries and Oceans Canada [DFO] 2021). For instance, coded-wire-tagging data for Chinook Salmon O. tshawytscha and Coho Salmon O. kisutch that were released over a 45-year period from 25 federally run or federally supported hatcheries throughout the province were recently used to evaluate the effects of altering hatchery release practices on juvenile-to-adult survival and to provide recommendations for optimizing hatchery operations (James et al 2023). There are also ~70 relatively small "public involvement hatchery programs" (also termed "community hatcheries") that primarily operate to provide education and facilitate public engagement but also work to support local salmon populations (A. Silverstein, Salmonid Enhancement Program, Fisheries and Oceans Canada, personal communication).…”

Hatcheries to high seas: climate change connections to salmon marine survival

“…The Japanese chum salmon hatchery programme recommended a release size greater than 1 g (BW) and a release time when the coastal SST ranged from 5 to 13 °C (Honda et al, 2020). Increasing body weight (BW) at release has been associated with increased return rates of chum salmon (Saito & Nagasawa, 2009), and survival of Chinook and coho salmon (James et al, 2023). We selected release events with no missing measurements of BW and fork length (FL) for Hokkaido and Honshu from the FRA salmon database (Data S1).…”

“…The return rate has been widely used as a common measure of the effectiveness of marine stock enhancement, including salmonids (Kitada, 2018). It has been used as a measure of the relative survival of chum salmon (Kaeriyama, 1999; Saito & Nagasawa, 2009), Chinook and coho salmon (James et al, 2023). It is generally accepted that hatcheries are responsible for most of the chum salmon in Japan and that there are no wild chum salmon (Hiroi, 1998; Kaeriyama, 1999; Kaeriyama & Edpalina, 2004; Kobayashi, 1980; reviewed by Iida et al, 2018).…”

“…Increasing body weight (BW) at release has been associated with increased return rates of chum salmon (Saito & Nagasawa, 2009), and survival of Chinook and coho salmon (James et al, 2023). The Japanese chum salmon hatchery program recommended size at release greater than 1 g (BW) and time of release when coastal SST ranged from 5 to 13 °C (Honda et al, 2020).…”