Rivers Inlet sockeye salmon (Oncorhynchus nerka) declined dramatically in the last decade. Stock assessment data has pointed to a downturn in marine survival as a likely cause. Four years of inlet surveys have generated evidence of the following:
that juvenile sockeye salmon use the inlet as a staging area that inlet salinity patterns are highly variable, that the juvenile migrants appear to congregate in areas of moderate surface salinity, and
- that they can more than double their weight as they feed in the inlet.
In addition, an exploratory statistical analysis showed that marine survival for these migrants is negatively correlated with early-spring river discharge preceding the late-spring juvenile migration. This suggests that heavy freshwater discharge floods the inlet surface with nutrient-poor, often turbid water, and thereby diminishes plankton growth in the lead-up to the juvenile migration. Other evidence also points to potential influence from broad-scale ocean circulation phenomena.
We propose to assess this potential explanation through:
- building a hydrodynamic model of the inlet, and
- using satellite imagery and ocean pressure gauges, where possible, to assess phytoplankton productivity and water conditions near the inlet.
This research will involve the integration of a complex, deterministic hydrodynamic model with equally complex oceanography data, and highly stochastic data from biological samples. Furthermore, by integrating physical and biological data, it will address a priority research area for DFO. Finally, the collapse of Rivers Inlet sockeye salmon has had a major impact on the commercial salmon fishery and has devastated the cultural and economic foundation of the Oweekeno First Nation. Hence, this research project would provide a high public profile to the work of the NPCDS.