Salish Sea Marine Survival Project

37 0.030 0.025 0.020 0.015 0.010 0.005 0.000 1995 2000 2005 2010 2015 COWICHAN CHINOOK MARINE SURVIVAL Figure 4. Cowichan River Chinook marine survivals — solid line and dots are estimated marine survival rates from a stock assessment model. Blue crosses are the Chinook marine survival rates fitted to a model with Sea Surface Salinity at Entrance Island, Sea Surface Temperature at Chrome Island and the annual anomaly of the total zooplankton biomass as the predictor variables. Red triangles represent marine survivals and their 95% confidence intervals for Cowichan Chinook Salmon predicted from this model for missing years 2005 and 2018. This model can be interpreted to mean that the marine survival of Cowichan Chinook Salmon is better when the salinity is lower, the sea temperature is warmer and total zooplankton biomass is higher in the years when the fish enter the Strait of Georgia. Note that years 2011 and 2017 were fit poorly by this model – this suggests that other factors which are not included in this model may have been important in these years. Graph provided by Ian Perry, DFO. SUMMARY OF RESULTS TO DATE This project studied the relationships between salmon conditions (abundance, marine growth, survival) with their food sources. It identified the bi-weekly patterns in abundance, biomass and locations of zoo/ichthyoplankton, including species thought to be major prey items. Preliminary analyses indicated significant relationships between certain physical conditions in the Strait of Georgia, the biomass of some zooplankton taxa which appear to be key food items for juvenile Coho and Chinook Salmon, and the marine survival of Coho and Chinook populations which enter the northern Salish Sea. Regions within the Salish Sea with higher and lower than average plankton concentra- tions ('Hotspots' and 'Lowspots') are being identified on a biweekly basis throughout the Salish Sea for comparisons with juvenile salmon distributions, timing and growth. Key findings include: Total zooplankton biomass in Central and Northern Strait of Georgia has generally been above average since 2010 (Figure 3); In general, crustaceans showed a U-shaped pattern over time, with lowest biomasses during 2002-2009; several crustacean zooplankton species are important diet components for juvenile salmon in the Salish Sea. In contrast, many species of gelatinous plankton (which are not good as fish food!) have been increasing since 1995; A number of physical variables appear to be important to patterns in zooplankton including: the annual magnitude of the flow from the Fraser River, the average vertical water temperature measured off of Nanoose Bay, the annual wind stress measured at Sand Heads at the mouth of the Fraser River and the timing of the spring phytoplankton bloom in the Central Strait each year; and Results of modelling the annual marine survival of several Chinook and Coho stocks which enter the Strait of Georgia are showing promising relationships. For example, marine survivals of Cowichan River Chinook Salmon are strongly related to sea surface salinity measured at Entrance Island, sea surface temperature measured at Chrome Island and the annual anomaly of the total zooplankton biomass in the year these animals first enter the ocean (Figure 4). Photo by Jeremy Koreski NEXT STEPS A consistent zooplankton monitoring program in the Salish Sea can assist with projections of future abundances of juvenile salmon. The initial funding for this project from the Pacific Salmon Foundation has re-energized interest and sampling of the lower trophic levels in the Salish Sea, and their connections with environmental drivers and connec- tions to juvenile salmon. The positive early results from this program enabled the DFO research team to obtain support for the use of DFO funds and ship time to continue this sampling throughout 2018 and to the present.

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