Using salmon to sample the Salish Sea: diets of recreationally harvested Chinook and Coho salmon as an ecosystem monitoring tool

In addition to their economic, social and cultural importance, Chinook and Coho Salmon are key players in the Salish Sea ecosystem. They are at times dominant predatory fish in epipelagic waters and are important prey for marine mammals. Chinook Salmon in particular are critically important as the primary prey of the endangered Southern Resident Killer Whales. Surprisingly, data on the diets of adult Chinook and Coho Salmon in the Canadian Salish Sea (Straits of Georgia and Juan de Fuca) are sparse, with no published work since the 1980s and a total lack of information on winter diets. We are seeking, in partnership with recreational anglers, to develop a low-cost, ongoing program to sample Chinook and Coho Salmon diets throughout the year from around the Canadian Salish Sea. We report results of our pilot year (2017) which indicate regional and seasonal variation in Chinook Salmon diet and corroborate recent observations of forage fish dynamics in the Salish Sea. This program has the potential to complement existing and future fishery-independent surveys in elucidating natural and anthropogenic changes in the ecosystem. We welcome input from, and collaborations with, other Salish Sea researchers to maximize the value of this citizen science initiative

A case study of fine scale habitat use by first ocean year Chinook salmon: implications for growth and predation exposure

Epipelagic habitats occupied by juvenile Chinook Salmon in the Salish Sea are structured at fine scales by tidal currents, wind, and topography. How juvenile salmon distribution interacts with this structure may have implications for diet, growth, and exposure to predation. We have developed two adjacent (~ 4 km apart) sites in the Southern Gulf Islands with differing oceanography as a case study of juvenile Chinook Salmon habitat use in late summer and fall of their first ocean year. We characterized the physical and biological oceanography of these sites with a combination of temperature profiles, zooplankton sampling, and hydroacoustic surveys. Using a flexible, low cost, small vessel based approach (microtrolling), we investigated distribution, diet and growth of juvenile Chinook Salmon between July and October. We also employed acoustic telemetry to directly measure Chinook Salmon movements within and around our study area. Our results suggest that individual juvenile Chinook Salmon, even of the same age and stock, behave differently. Differing patterns of habitat use could be related to trade-offs between growth and predation exposure. Predation and failure to reach a critical size prior to winter are two leading hypotheses to explain depressed marine survival of Salish Sea Chinook Salmon. Our work suggests that fine scale processes should be taken into account when evaluating these hypotheses