The Yukon River Chinook Run Timing Project is a collaboration between the Alaska Department of Fish & Game, the National Oceanic and Atmospheric Administration, and the Alaska Ocean Observing System.
Yukon River Chinook are expected to arrive on the Yukon River Delta with average run timing in 2026: The first significant pulse (15% point) is expected by June 12th and 50% of the run is expected to arrive by June 20th. Note that the forecast model used this year is less powerful than the one used in previous years. This change is due to the discontinuation of sea surface temperature and sea ice data products used normally. See Project Status section for more detail and for information on future plans for the project.
Moderate air temperature at the Nome, AK airport during the month of April is generally associated with average run timing (Mundy & Evenson 2011)1. In 2026, April mean air temperature at the Nome, AK airport (AMATC) was -5.4°C, slightly warmer than the long-term average of -6.6°C (range -17.1°C to 1.3°C).
Figure 1: Scatterplot of median Yukon River Chinook run timing (MDJ) against April mean air temperature at the Nome, AK airport (AMATC). A solid vertical bar at -5.4°C marks the observed value for AMATC in 2026.
Forecast Detail
The forecast model is based on the relationship previously established in Mundy & Evenson (2011)1 which identified a set of three environmental variables that correlate with the run timing of Yukon River Chinook: April mean air temperature at the Nome, AK airport (1961–2026; AMATC), May mean sea surface temperature (1961–2025; MSSTC) in the nominal marine staging area just off the Yukon River Delta, and the Spring-time proportion of ice cover (1970–2025; PICE), also measured over the nominal marine staging area. The forecast model for 2026 is based only on AMATC due to data availability.
The forecast model is made of three independent sub-models, where each sub-model is a multiple linear regression with a response of either the 15th (FIFDJ), 25th (QDJ), or 50th (MDJ) percentile of cumulative catch-per-unit effort (CPUE) in either commercial or test fisheries located on the delta (1961–2023). Note the time series of CPUE data ends in 2023 due to changes in the operation of the Lower Yukon Test Fishery.
Based upon the historical relationship with CPUE in commercial and test fishery catches on the Yukon River Delta (1961–2023) and AMATC, the predicted dates of three percentiles of CPUE in the Lower Yukon Test Fishery are June 12th (15%), June 15th (25%), and June 20th (50%) (Table 1).
Table 1: Predicted dates (June 12th, 15th, 20th) of three percentiles (15%, 25%, 50%) of cumulative catch-per-unit-effort (CPUE) and the associated model formula for each.
Forecast Performance
We quantified the accuracy of the forecast sub-models with a hindcasting approach, using the most recent fifteen years of runs. For each sub-model, we calculated a set of prediction-oriented evaluation criteria (Table 2). All three sub-models (FIFDJ, QDJ, MDJ) perform similarly, with mean absolute prediction errors (MAPE) 3.87–4.40 days. We calculated prediction intervals by multiplying each model’s standard error by 2σ to get prediction interval widths ranging from 5.5–6.1 days which contained the observed run timing 40–53% of the time. Last, we calculated the maximum absolute residual to be 10–12 days and prediction bias to be -4.4 to -2.4 days. A negative value for bias means the model tends to forecast earlier than observed run timing. The forecast’s bias is an area for future forecast improvements.
Table 2: Model performance metrics for the three sub-models that make up the forecast. MAPE: Mean Absolute Prediction Error and its standard deviation. Bias is the mean residual. Max. Residual is the maximum absolute residual.
Project Status
As mentioned above, this year’s forecast uses a reduced model due to the discontinuation of the data products associated with the MSSTC and PICE variables used in the full model. MSSTC is derived from NCEP-NCAR Reanalysis 1 which has been discontinued and replaced by CORe as of March, 2026. PICE is derived from Near-Real-Time DMSP SSMIS Daily Polar Gridded Sea Ice Concentrations, Version 1 which has been replaced by an AMSR2-based product as part of the National Snow and Ice Data Center’s replacement of its SSMIS-based products. Attempts were made to evaluate the replacement data products but initial results show more work is needed to integrate them into the forecast.
The loss of these two data products is significant but isn’t the only change affecting this project. Since 2024, the Lower Yukon Test Fishery hasn’t operated sites specifically for Chinook. This means the CPUE data series used in both the full and reduced models ends in 2023 and forecast models are no longer being fit to the most recent previous runs. These two changes indicate a new modeling approach is likely needed in order to produce a useful forecast product.
Therefore, we plan to put the project on hold for the foreseeable future and this will be the final forecast for the project in its current form. We’ve already reached out to agency and academic partners and plan to update our AOOS project page with any future updates on project status.
More Information
See the project website for more background on the project. For more information about how the forecast was produced, see https://github.com/yukon-forecasting/2026-forecast. For more information on the forecast model and the underlying biological hypothesis this forecast is based on, see Mundy & Evenson (2011)1.
Acknowledgements
Prepared by Bryce Mecum (brycemecum@gmail.com). Web page support by Alice Bailey (bailey@aoos.org) and Alaska Ocean Observing System. Yukon Chinook in-season salmon data and management agency coordination by Fred West (fred.west@alaska.gov). Financial and material support provided by the Alaska Ocean Observing System, NOAA National Marine Fisheries Service, and the Alaska Department of Fish & Game.
References
[1] Phillip R. Mundy, Danielle F. Evenson, Environmental controls of phenology of high-latitude Chinook salmon populations of the Yukon River, North America, with application to fishery management, ICES Journal of Marine Science, Volume 68, Issue 6, July 2011, Pages 1155–1164, https://doi.org/10.1093/icesjms/fsr080
Read more about the Yukon River Chinook Run Timing project here.