Salish Sea Marine Survival Project

82 CONCLUDING REMARKS The Salish Sea Marine Survival Project (SSMSP) was designed as an intensive, short-term project of the Salish Sea ecosystem to study the major components of the salmon ecosystem simultaneously; evaluate the marine survival of Chinook, Coho and steelhead; and identify the primary determinants of survival/production of these species. As our findings accumulate, we have begun to develop a picture of what is happening to our juvenile salmon and steelhead as they traverse the Salish Sea marine environment. The details of many of the Canadian SSMSP studies and methods were summarized in the previous chapters; here we begin a synthesis of our results. The journey for salmon and steelhead begins and ends in rivers but they spend the majority of their lives in the ocean. Consequently, the determinants of abundance may occur in freshwater, estuaries and the ocean; and likely some portion within each. In this life cycle diagram, the abundance of salmon that returns from the ocean began years before (in the brood or spawning year for the parents) and varies with the number of spawning adults and survival of the eggs to emerging juveniles (Figure 1). Juvenile use of freshwater streams varies by species from a few months to a few years and survival is habitat (flows, food availability and shelter) and predator dependent. As juveniles prepare to emigrate to the sea, they transform into 'smolts' (juveniles that are physiologically able to enter salt/marine waters) and begin a downstream migration to the estuary and ocean. Smolts use estuaries as transition habitats but to varying degrees, again depending on the species, and gradually move into nearshore waters. This transition to fully marine waters (identified in the diagram by the red, dashed circle and red arrow) is hypothesized to be the 'critical period' in the determination of salmon abundance from each brood year, and occurs over several weeks. The juveniles that survive continue migration through marine waters until they begin to mature and return to their freshwater stream of origin. As these adults return, they now face fisheries and other predators, and physiologically must revert back to freshwater environ- ments. Ultimately their life-cycle ends when adults return to their 'home' streams to spawn and die (Pacific Salmon only spawn once, but steelhead can spawn multiple times). The complex and highly-migratory life of Pacific Salmon makes resolving the primary determinants of their annual abundance very difficult, particularly when humans have extensively altered every habitat that they depend upon. But evidence to date suggests that the 'critical period' is a primary determinant of annual variation in adult returns, and for local populations of Chinook, Coho and steelhead, that the Salish Sea has the greatest effect. However, this critical period reflects the current conditions of habitats, competition and predation in both freshwater and marine environments, but its magnitude may not have been so pronounced under more pristine conditions or if we could mitigate impacts. Spawning Incubation Emergence Freshwater Rearing Freshwater Rearing R I V E R O C E A N Estuary Rearing Migration to Rearing Areas Migration to Spawning Areas Growth & Maturation Figure 1. Generic life cycle diagram for Pacific Salmon. The danger icon shows the period that has been hypothesized to be the "critical period".

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