Science Response 2015/028
Supplement to the pre-season return forecasts for Fraser River Sockeye Salmon in 2015
Context
Sockeye that spawn and rear in the Fraser watershed (i.e. Fraser Sockeye) exhibit two distinct life-history types: lake-type (Figure 1) and river-type (Figure 2). Most Fraser Sockeye are lake-type, including the Chilko stock, which is expected to contribute the largest proportion to the total Fraser Sockeye return in 2015 (35%). The predominant age class of lake-type Fraser Sockeye is four year olds. After spending their first two winters in freshwater (one winter as eggs in spawning gravel and one winter as fry in rearing lakes), lake-type Fraser Sockeye yearling-smolts migrate rapidly out of their rearing lakes, down the Fraser River, northward through the Strait of Georgia (SOG) and Johnstone Strait, and along the continental shelf, en-route to the Gulf of Alaska. They spend their final two winters in this ecosystem before returning to spawn (Figure 1).
River-type Sockeye spend a single winter in freshwater, and migrate downstream to the SOG as sub-yearling smolts shortly after emerging from their spawning gravel. Harrison Sockeye, the largest river-type stock in the Fraser watershed (this stock is expected to contribute 21% to total return in 2015), remains in the SOG for several months, after all lake-type Fraser Sockeye stocks have migrated out of this system, and subsequently migrate out into the northeast Pacific via the southern Juan de Fuca Strait route (Figure 2). This stock returns to spawn as three and four year olds.
For both life-history types, mechanisms influencing Fraser Sockeye survival are complex and poorly understood, due to the broad range of ecosystems they inhabit throughout their life-history. This increases uncertainty in the Fraser Sockeye forecasts. To improve our understanding of Fraser Sockeye survival mechanisms, starting in the 2014 forecast year (DFO 2014a), auxiliary information on the parental spawner generation through to the juvenile marine rearing environment is synthesized in a forecast supplement report (DFO 2014b). What was learned retrospectively from this first process is presented in Appendix 1 of the current paper.
To provide context for the 2015 forecast (DFO 2015), this year’s Fraser Sockeye forecast supplement report focuses specifically on the 2011 brood year for lake-type stocks, and the 2011 and 2012 brood years for river-type stocks (i.e. Harrison Sockeye). This report synthesizes information on the adult migration conditions, escapement and spawner success, fry and their lake rearing conditions, smolt and juvenile migration, and ocean conditions. In addition, stock compositions of the 2011 escapements, 2013 downstream smolt migration, juvenile ocean migration, and 2015 return forecasts are compared to evaluate proportional changes in stock composition through time. The 2014 forecast supplement report (DFO 2014b) can be used, in combination with this report, to provide context for the five year olds returning in 2015 (DFO 2015).
This Science Response Report results from the Science Response Process of January 27-28, 2015 on the Supplement to pre-season abundance forecasts for Fraser River Sockeye Salmon returns in 2015.
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