Salish Sea Marine Survival Project

44 Other studies in the Cowichan noted that hatchery-reared smolts were larger than wild smolts, ate larger prey, spent very little time in the estuary, and disappeared from the bay earlier, due to emigration or mortality. The larger body size may be a disadvantage for hatchery smolts if it neces- sitates their leaving the estuary prematurely to meet food needs. The onset of piscivory (when smolts begin to feed on forage fish) began at a fork length of approximately 74 mm, which was less than the average fork length of the hatchery (clipped) fish in this study. Leaving the safety of nearshore habitats, especially those providing eelgrass and kelp cover, may expose hatchery fish to increased predation risk and account for the lower survival rates of hatchery fish compared to wild fish. Copepods were conspicuously absent from the diet of young Chinook Salmon in Cowichan Bay. Continued log-booming activities in the north-western part of Cowichan Bay and the Cowichan River estuary have altered the substrate. The constant shedding from logs and lack of sunlight make the substrate inhospitable to eelgrass and the many organisms that live in eelgrass ecosystems including harpacticoid copepods, a favoured prey of Chinook Salmon smolts. Decomposing bark and wood on the bottom of the ocean also release toxins, such as log leachates, which are lethal to fish. Eliminating log booming (in shallow marine environments) and restoring eelgrass beds would improve salmon habitat quality in Cowichan Bay, and more broadly. Washington Department of Fish and Wildlife (WDFW ) staff learned that small juvenile Chinook migrating out of North Puget Sound rivers (Nooksack and Skagit) and from the Cowichan River early in the season have a much greater chance of surviving to return as adults when compared to populations from Mid and South Puget Sound (Cedar, Green, Puyallup). Mid and South Puget Sound watersheds have limited estuary habitat compared to North Puget Sound rivers, which may account for the low survival of fry-sized fish in those populations (Figure 4). This work is currently being extended to include more Strait of Georgia systems which will allow for a more complete transboundary analysis, and may reveal whether a relationship between survival rates and presence of intact estuary habitats holds for the whole Salish Sea. If this is the case, there will be an extremely strong case for increased protection and restoration of estuaries. 3. Losses of these Important Habitats Globally, seagrass ecosystems are declining in area by about 5% per year due to anthropogenic stresses, including decreased water quality and increased water temperatures. SSMSP researchers have been assessing the overall decline or degradation of eelgrass nursery areas in the Strait of Georgia over the period from 1932- 2016 using historic aerial photographs and Unmanned Aerial Vehicle (UAV ) or drone imagery. They found that increasing fragmentation and loss of eelgrass beds were associated with shoreline activities (boats, docks, log booms and armouring) and increased housing density in the three estuaries chosen for study. The results suggest an overall deterioration of coastal environmental health in the Salish Sea due to increased use of the coastal zone, as well as declines in water quality due to urbanization. Other studies have identified reductions or loss of kelp beds in many regions of the Strait of Georgia, particu- larly in the northern and central Salish Sea, while other beds appear to persist (e.g., in Sansum Narrows, Dodds Narrows, Mayne Island, Saratoga Beach and Burrard Inlet side of Stanley Park). At present, the majority of kelp mapping is conducted manually via transects and aerial photography. Though effective, the strategy is labour-in- tensive, requires large time investment and is limited by the areas surveyed. Under SSMSP, there has been a recent breakthrough as one study has highlighted the utility of satellite imagery for mapping kelp beds, delineating the distributional changes and losses of kelp is ongoing. 4. Limiting Factors for Kelp and Eelgrass SSMSP funded restoration projects for both kelp and eelgrass in many areas around the Strait. These projects have also elucidated many of the limiting factors to survival of these species. Kelp shows distinct responses in terms of decreased reproductive activity when waters are warm, and rising ocean temperatures are thought to be a major contributor to kelp declines. Eelgrass restoration activities have been successful in many areas of the Strait, but are hampered due to the damage by anchors and anchor chains, dock building and shoreline hardening. Restoration is also hampered if large quantities of marine debris fragment the eelgrass beds. Figure 3. Beach seining in Cowichan Bay for juvenile Chinook Salmon.

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