Science Advisory Report  2016/008

Run Timing and Diversion Rate Models for Fraser River Sockeye

Summary

• Fisheries and Oceans Canada (DFO) Fisheries Management has requested that Science Branch provide advice for pre-season forecasts of adult Fraser Sockeye Salmon (Oncorhynchus nerka) marine run timing and diversion rate (the proportion of fish migrating through Johnstone Strait versus Juan de Fuca and Johnstone Straits combined). 
• Numerous models to explain the relationship between observed migratory patterns of Fraser River Sockeye Salmon (the run timing and the northern diversion) and environmental correlates - including ocean surface currents, wind stress, and geomagnetic fields - were developed, and measures of performance - including precision and accuracy - were calculated. These data sources are updated frequently enough to allow their use for pre-season forecasts.
• A list of top-ranked models has been identified based on performance metrics. Relative performance of the models is presented as probability-based forecast certainty plots to guide managers and analysts in the selection of models. Multiple variable models perform better than single variable models, and current velocity variables (OSCAR - Ocean Surface Current Analyses – Real time, and NEPSTAR - North East Pacific Salmon Tracking and Research) dominate top performing models. It is recommended that the ranking process be undertaken annually until its robustness across multiple years is determined.
• The models examined provide statistical relationships to forecast run timing and northern diversions based on data collected from 1983 to 2012, and assume these years represent typical conditions. The forecasting of atypical events requires further model assessment based on management risk tolerance criteria.
• The ranking of the top performing models assumes a neutral weighting for bias and precision. This approach for ranking does not reflect specific objectives provided by fisheries managers, and it is recommended fisheries management consider the merits of this weighting during the pre-season, prior to selecting which models to use for the annual forecasts.
• A separate examination of El Niño and non-El Niño years revealed El Niño conditions during May or June of the return year are associated with a later Early Stuart run timing. Later Chilko run timing occurs when El Niño conditions are observed over any time between December and May of the return year. El Niño conditions in any month between September of the year prior to adult return, and May of the return year, are associated with a significantly higher northern diversion.
• Many of the models developed are dependent on data that are currently publicly available, but sourced from external agencies (e.g. National Oceanic and Atmospheric Administration [NOAA]). Others are dependent on contractors (NEPSTAR) and require an annual financial commitment.
• The evaluation of thousands of statistical relationships between environmental variables and fisheries data to identify an ensemble of models based on performance metrics is an approach that can be applied to other areas of fisheries management. An understanding of the underlying biophysical relationships provides confidence in how to interpret the statistical relationships, and insight into conditions that influence the strength of the relationships.

This Science Advisory Report is from the October 27 – 28, 2015 regional peer review on the Run Timing and Diversion Rate Models for Fraser River Sockeye. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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