Salish Sea Marine Survival Project

74 To address the questions listed at the beginning of this summary (what, when, where and how did change occur?), this program needs to develop a suite of models for the Canadian Salish Sea, including: 1) A hydro-dynamic model that describes the physical environment of the Salish Sea at a fine time and spatial scale, considering historic weather, river runoff and ocean conditions (hour by hour and day by day); 2) A biogeochemical model that estimates plankton productivity; 3) A food web model that describes how predator and prey populations interact, how they occur spatially and how they have been impacted by humans, notably through fishing and habitat changes; and 4) A behaviour model that follows historic releases of Chinook and Coho Salmon smolts (hatchery and wild) as they come out of the rivers and evaluates how their survival may have been impacted by predators and prey during their first year in the Strait. The initial hydro-dynamic and biogeochemical models have been developed and progress is ongoing. Once the food web model is complete, the hydrographic/biogeo- chemical and food web models will be inter-connected. This will then allow for evaluation of the relative impact of changes in environmental productivity, food web structure and direct human impacts on the population trends for salmon and other key ecosystems groups in the Salish Sea. Figure 1: A schematic of the food web of the Strait of Georgia. Circles represent functional groups of species, the size of the circles represent biomass (log-scaled) and the lines indicate trophic (i.e., feeding) relationships. Figure provided by V. Christensen. This activity will be central for the SSMSP's primary research objective of assessing if "bottom-up processes driven by annual environmental conditions are the primary determinants of salmon production via early marine survival." SIGNIFICANCE This modelling approach will allow us to examine how environmental productivity, food web conditions (predator and prey factors) and human impacts have impacted salmon survival/production over time. However, under- standing and then testing our understanding of predator/ prey systems in this ecosystem is complex, as Figure 1 suggests! In Puget Sound, an independent ecosystem model is being developed. The Atlantis model is another 3D 'end-to-end' modeling approach that includes oceano- graphic, chemical, ecological (competition and predation) and anthropogenic processes. Atlantis is intended as a strategic management tool to evaluate hypotheses about ecosystem response, to understand cumulative impacts of human activities and to rank management options. Developing a second independent model is one of the only means to really test our understanding of these complex marine ecosystems. During SSMSP and continuing with Adult Chinook and Coho diet studies at the University of Victoria and PSF, otoliths have been collected from stomach contents of adult salmon and from the scat of harbour seals and other mammalian and bird predators to provide information on their diets that we can observe today.

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