Science Response 2016/047
Supplement to the pre-season run size forecasts for Fraser River Sockeye Salmon (Oncorhynchus nerka) in 2016
Context
To provide background for the 2016 Fraser Sockeye returns (DFO 2016), this year’s Fraser Sockeye forecast supplement presents information on these fish from their spawning parents through to their three-year-old siblings that returned in 2015. The brood year (year they were spawned by their parents) for 2016 four-year-old lake-type Fraser Sockeye returns, which represents most stocks, is 2012. The brood year for three and four year old river-type Sockeye (Harrison) returns are 2013 and 2012, respectively. The forecast supplement synthesizes information on adult Fraser River upstream migration conditions, escapements, spawner success, fry abundance and condition, the lake rearing conditions for fry (if available, and applicable to lake-type stocks only), and juvenile migration and ocean conditions in the Fraser River and Strait of Georgia (SOG). In addition, proportions of key lake-type stocks in various sampling components of the 2012 brood year are compared: 2012 escapements, 2014 smolt Fraser River downstream migration, 2014 juvenile ocean migration, and 2016 return forecasts.
Based on the 2016 Fraser Sockeye return forecasts, the stocks expected to contribute the largest percentages to the 2016 returns include the lake-type Chilko stock (44% of the forecast return at the 50% probability level), Late Stuart and Stellako stocks (combined contribute 20% to the forecast return) and the river-type Harrison stock (8%) (DFO 2016). The Chilliwack lake-type stock is also expected to contribute a larger proportion (6%) than average to the total return, given its exceptional brood year escapement in 2012 (DFO 2016). Given the differences in ages, life-history, and ocean distribution, lake-type stocks are considered separately from Harrison, the only large river-type stock in this system.
There are mixed survival signals for 2016 Fraser Sockeye returns. Some indicators suggest survival could be poor, whereas other indicators suggest survival could be average or better. The ‘warm blob’ has persisted during the ocean residence of both the 2015 returns and the upcoming 2016 returns, affecting the environmental conditions experienced by these fish. However, given the mixed survival responses across Sockeye stocks in 2015, no conclusion can be drawn regarding the potential effects of the continued persistence of the ‘warm blob’ in the Northeast Pacific Ocean on 2016 returns.
New information from the Mission smolt project in the lower Fraser River and the expanded SOG surveys provide enhanced resolution on the out-migration timing and distribution of Fraser Sockeye stocks throughout both the lower Fraser River and the SOG. Combined with assessments of ocean conditions, these projects have the potential to link smolt out-migration timing and distribution in the Fraser River and SOG to temporal and spatial variation in ocean conditions. However, large gaps remain in the marine assessments, particularly outside the SOG, required to link changes in Fraser Sockeye survival to marine conditions. Similar gaps remain in understanding the influence of freshwater factors on Fraser Sockeye survival. No assessments of spawning habitat are conducted, and assessments of lake ecosystems have remained limited and sporadic.
This Science Response Report results from the Science Response Process of January 21-22, 2016 on the Supplement to the pre-season abundance forecasts for Fraser River Sockeye Salmon returns in 2016.
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