Northeastern Bering Sea Juvenile Chinook Salmon Survey 2017 And Yukon River Adult Run Forecasts 2018 2020 PDF Download

Monitoring of juvenile Yukon River Chinook salmon Oncorhynchus tshawytscha stocks rearing in the Northeastern Bering Sea (NBS) was initiated by the National Oceanic and Atmospheric Administration (NOAA) in 2002 using a pelagic trawl survey program. Juvenile salmon were caught after their first summer at sea, and prior work has demonstrated a clear relationship between juvenile abundance and future adult returns, enabling the use of juvenile data in adult run size forecasts. The estimated abundance of juvenile Chinook salmon in the NBS was approximately 2,480,000 (SD 439,000) in 2017, below the 2003-2016 average. The mean proportion of 2017 NBS juvenile Chinook salmon originating in the total Yukon River and Canadian-origin Yukon River was 72% (SD 5%) and 42% (SD 4%), respectively. Abundance of total Yukon and Canadian-origin stocks were estimated as 1,774,000 (SD 338,000) and 1,049,000 (SD 207,000), respectively. Previously established and new adult Yukon River run reconstructions were used to evaluate relationships between juvenile abundance and adult abundance of spawners, runs, and returns. A marked decrease in juvenile production (juveniles per spawner) for total Yukon River and Canadian-origin stocks was below their 2003-2016 averages. These data were incorporated into forecast models to predict total adult run size. Forecasted total Yukon River Chinook salmon run sizes for 2018-2020 were 179,000-301,000, 170,000-297,000 and 114,000-230,000, respectively; forecasted Canadian-origin Chinook salmon run sizes for 2018-2020 were 65,000-102,000, 74,000-116,000 and 62,000-105,000, respectively. The date-adjusted length (FL) of juvenile Chinook salmon in the NBS was 204 mm in 2017, below the 2003-2016 average of 212 mm. Marine data on juvenile Chinook salmon clearly demonstrate that Yukon River Chinook salmon should be expected to remain in a relatively low productivity regime in the near future, but record-low run abundance is unlikely through 2020.