Calibration and multi-year synthesis of 7 years of data from the Mission Juvenile Sockeye Project evaluating the abundance and stock composition of downstream migrating juvenile Sockeye in the lower Fraser River, 2012-2018

While Fraser River Sockeye Salmon survival has declined over the past decade it has also exhibited high inter-annual variability. The processes responsible for this trend and the variability are not understood and require continued investigation. Partitioning mortality among important life history stanzas (e.g. freshwater rearing, downstream migration, ocean entry) is required to understand when and where production limitation occurs so that it can be incorporated into production forecasting models. The early marine period has been identified as a period of high mortality and a critical stage in determining brood year strength for this species. However, the mechanisms associated with this mortality, as well as the role the annual abundance of juvenile Fraser Sockeye entering the Strait of Georgia (SoG) plays, are unknown. Freshwater survival (from egg deposition to lake out-migration) is estimated for only two Fraser River Sockeye Salmon stocks annually. Currently, marine survival combines mortality across many important life history stanzas (downstream migration, ocean entry, marine rearing), providing little ability to identify or resolve important production limiting processes. Data collected from a juvenile trapping program in the lower Fraser River from 2012 through 2018 provided the first opportunities to identify when specific Sockeye stocks (CU’s) make their entry into the SoG. This information will assist in identifying production processes across many important life history stanzas and help explain observed survival trends.
This project will allow the hiring of a biologist to further the analysis already performed annually on data collected with operational funding provided by the PSC Southern Fund (2012-2016) and DFO (2017-18), and in-kind support from the DFO (2012-2016). These data have shown there are significant stock differences in downstream migration timing and relative abundance among Fraser Sockeye juveniles, both within and among years. This work will allow the development of new juvenile based models. Juvenile based models have shown to be the higher performing models for forecasting Sockeye Salmon returns where we have long juvenile time series (Chilko and Cultus Sockeye Salmon).