Salish Sea Marine Survival Project

84 In support of the 'critical period' during early marine life, are: Coherence of survival patterns across multiple popula- tions when in a common environment; Demonstrated targeted predation by seals and birds during this transition stage; Greater survival of the faster growing individuals; and Survival of tagged larger Chinook (in September/ October) was 2.25 times greater than survival of smaller Chinook tagged in May. When all our results to date are considered, a more comprehensive interpretation of Chinook and Coho production at a population level may be a chain of events and each link in the chain may vary in strength between years. The effect of a following link may be positive (compensatory) or negative (depensatory) but only within bounds determined by the net effect of the previous links. Essentially all bottom-up and top-down factors identified in the Introduction had some effect. Chinook and Coho that survive to the early marine phase grow very rapidly during the first months, show behaviours that enhance energy consumption and display variation in migration patterns between populations. Variation in survival between individuals within a population provides the opportunity for adaptation to changing environmental conditions and sustaining local populations. The 'critical' aspect of the early marine phase for individuals may be to achieve a growth threshold/ condition in their first summer at sea in order to survive the subsequent fall/winter conditions. Based on our observations, what management actions may be taken to improve production of Chinook and Coho Salmon? A wide variety of actions could improve produc- tion but given the diversity of factors that act sequentially through the salmon life cycle, many of the actions would also have to be taken simultaneously. Restoration projects should therefore be broad-based, coordinated and moni- tored in order to assess limiting factors and track net gains in restoration. These actions may include: Protection of environmental flows in freshwater systems (under BC Water Sustainability Act, 2014); Estuary restoration and management of log-booms; Management of salmon predators during the vulnerable early migration period; Nearshore habitat restoration, particularly for marine grasses and kelps; Forage fish restoration and habitat protection/ restoration; Artificial enhancement projects to supplement natural production and diversity, assuming we can achieve a net gain in production and population diversity; and Harvest management impacts appropriate for the productivity rate in naturally spawning populations. However, under the 'critical period' hypothesis, much of the variation in salmon production will be driven by annual variation in weather and resulting biological ocean- ographic conditions in the Salish Sea. The actions above may ameliorate (reduce) the magnitude of variation but are unlikely to compensate for these large scale effects. In which case, the ability to predict consequences (by understanding the ecological interactions) and to take necessary management responses is a required outcome of our research. To integrate multiple environmental changes within the Salish Sea, a continuing study within the SSMSP is the development and testing of two ecosystem-based computer models by the University of BC (Dr. V. Christensen) and the National Oceanographic and Atmospheric Administration (Dr. C. Harvey). These independent models are being developed to test our understanding of mechanisms driving this salmon ecosys- tem. Once completed, these tools will enable researchers to go back in time to assess the causes of changes in production and to provide forward projections (forecasts) of how current environmental conditions may change and affect salmon production. Such models are the only means to objectively test our understanding of the Salish Sea, effects on salmon production and future expectations.

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