Salish Sea Marine Survival Project

77 RESEARCH TOPIC OUTCOMES Biological Oceanography (continued) Surface waters of the Salish Sea in the winter are corrosive as a result of lowered pH; impacts on the marine food web are being assessed. In general, there appear to have been two key time periods for zooplankton: 1996-2006, a period of generally declining zooplankton biomass and increasing salinities, and 2007-2018, a period of increasing zooplankton biomass and decreasing salinities. Although this recent increase in biomass should be good for forage fish and salmon, much of it was made up of an increasing abundance of gelatinous zooplankton ("jellyfish — not good fish food). Marine survival of three Strait of Georgia Chinook and one Coho population were best explained by models including zooplankton, sea surface salinity and other variables representing the flow from the Fraser River. Age-0 herring were heavier for a given length in 2007-2017 compared to herring sampled prior to 2007. This may have implications for juvenile Chinook and Coho, which are piscivorous. The increase in body condition of Young-of-Year (YOY ) herring since 2000 has likely resulted in only the largest juvenile Chinook able to prey on age-0 herring due to mouth gape limitations. Cowichan River Chinook Salmon Studies A significant number of studies of Cowichan Chinook were carried out during SSMSP, in freshwater and marine environments, including studies of: freshwater survival rates as related to flow conditions and predators; freshwater habitat requirements; application/ installation of Passive Integrated Transponder (PIT ) tags to assess relative survival of groups tagged at different times in their life history, to pinpoint bottlenecks to survival; development of a new sampling methodology called microtrolling; and a comparison of hatchery and wild Chinook survival rates. Mainstem and large side channel edge habitats with suitable velocities and intact over-stream and/or instream riparian vegetation cover were critically important for Chinook fry rearing. SSMSP saw a novel usage of PIT tags, strategically allocating PIT tags to salmon groups at different ages and locations to allow for a comparison of survival rates between groups (determined when fish return to natal streams as adults). Tagging groups from freshwater through their first year in marine waters allowed an examination of the differential survival rates as the fish grew and migrated seaward. Freshwater survival was surprisingly low some years (less than 30%) and appears to be related to level of discharge on the Cowichan River and possibly the result of predation. A high level of predation by herons, particularly on hatchery fish, was an unexpected finding. Microtrolling was a new SSMSP innovation to catch smolts using miniaturized trolling gear during their first summer/fall in marine waters. There appear to be two key mortality periods, during downstream migration of smolts to the ocean and then during the first winter. Hatchery fish survive about 35-40% as well as wild fish across all stages and it is believed that the mechanism controlling this difference likely occurs after their first summer at sea. These projects highlighted the importance of the first winter in the ocean, a period that has been little studied in the past. Nearshore Habitat Restoration and Research Numerous SSMSP projects assessed the usage of estuary and nearshore habitats, specifically marsh, eelgrass and kelp beds by juvenile salmonids. Estuaries are important for protection and rearing of juvenile salmon, especially of smaller fry, and allow for diversity in salmon production. Forage fish need specific habitat to lay their eggs, and these shoreline habitats require far more protection.

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