Salish Sea Marine Survival Project

43 Figure 1. Crabs attached to kelp. Photo by Sarah Schroeder. Figure 2. Fyke net used to capture salmon smolts in the Fraser estuary. Photo by Raincoast Conservation Foundation. HOW? Numerous SSMSP projects have focussed on Strait of Georgia nearshore habitats. These include studies to examine: 1. The use of kelp, eelgrass and other estuarine habitats by juvenile salmon; 2. The role of eelgrass versus non-eelgrass habitats for juvenile salmon diets; 3. The importance of intact estuarine habitat for juvenile Chinook life history diversity; 4. The impact of human disturbance on diversity of eelgrass beds and biodiversity; 5. The effects of temperature stress and herbivore grazing as limitations to bull kelp distribution; 6. The use of satellite imagery, aerial imagery, and drones to examine changes in the extent of bull kelp and eelgrass beds; and 7. The impact of temperature stress on kelp populations. Restoration and monitoring efforts for both bull kelp and eelgrass throughout the Strait have been ongoing over the course of SSMSP. FINDINGS TO DATE 1. Usage of Nearshore Habitats by Juvenile Salmon SSMSP snorkel and underwater video studies in the Cowichan estuary, Denman/Hornby Island and a number of other coastal regions around the Strait have observed the use of kelp and eelgrass beds by individuals and schools of juvenile salmon, forage fish and resident fish species (e.g., shiner perch, rockfish) and invertebrates (e.g., crabs, caprellid amphipods). Similarly, sampling in marsh channels, eelgrass and sand flats in the Fraser estuary across Roberts and Sturgeon banks showed highest total abundance and diversity of fish in eelgrass, followed by sand flat and marsh habitats. Of the estuarine habitats available, Chinook Salmon were found to particularly utilize the marsh channels but other estuarine and nearshore habitat types appear to be utilized in high density years. In the Fraser estuary , the most abundant Chinook were small ocean-type Harrison Chinook which showed high residency and dependence on estuarine habitats for growth. Juvenile Chinook and Coho Salmon diets contain harpacticoid copepods, a species which is highly associated with eelgrass habitats. One SSMSP study of stable isotope signatures in juvenile salmon showed high overlap with eelgrass stable isotope signatures, suggesting a large portion of salmon diet comes from eelgrass carbon where eelgrass is present. These results highlight the value of eelgrass in providing nearshore foraging opportunities for juvenile salmon. 2. Value of Nearshore Habitats A number of SSMP studies assessed the value of estuarine and nearshore habitats. Several studies showed evidence of decreased species richness and increasing simplicity of eelgrass fish communities in highly disturbed regions (e.g., sites within Fraser Estuary, Comox Estuary, southern Vancouver Island). Rockfish species, in particular, were an indicator species of low disturbance regions (sites within Clayoquot Sound, Barkley Sound, Central Coast and Skeena Estuary), whereas threespine stickleback were most asso- ciated with high disturbance regions. The higher diversity (within and among sites) of the fish community and the importance of commercially-valuable rockfish species within the community at low disturbance sites exemplifies the need to maintain and restore eelgrass habitats. In the Cowichan River, the estuary was particularly important to smaller fry as compared to stream-rearing Chinook that left the river at a larger size. High mortality rates for river- reared smolts in some years suggest that estuary-reared counterparts could have a survival advantage in some years and may be an important component of annual Chinook production. Estuaries in general provide an important role for protection and rearing, especially of smaller fry, and allow for diversity in salmon production.

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