Assessing regional patterns of juvenile salmon growth in the Salish Sea

Early marine juvenile growth in Pacific salmon is generally positively correlated with overall survival to reproductive age. In this study, regional patterns of juvenile salmon growth are being analyzed over a two-year period (2012-2013) in the Salish Sea and surrounding waters to better assess juvenile productivity, via growth, in the Salish Sea and surrounding waters to provide us insight into possible mechanisms regulating survival. Insulin-like growth factor-1 (IGF-1), a hormone used to assess instantaneous growth in fishes, including juvenile salmon, was measured in late June and early July of 2012 and 2013 in the Strait of Georgia, Johnstone Strait, Queen Charlotte Strait, and Puget Sound. Juvenile sockeye (Oncorhynchus nerka) and pink salmon (O. gorbuscha) were collected in 2012, whereas juvenile coho (O. kisutch), Chinook (O. tshawytscha), and chum salmon (O. keta) where obtained in both years. In 2012 IGF-1 levels were highest in pink salmon from the Gulf Islands and Puget Sound; this was a unique pattern among the 5 species of juvenile salmon sampled. Coho salmon IGF-1 levels were highest in samples from the Northern Strait of Georgia. Chinook salmon IGF-1 levels were significantly higher in the Strait of Georgia than Puget Sound. The only regions where IGF-1 values were consistently low for three of the four species were Queen Charlotte Strait and Johnstone Strait. Analyses of 2013 IGF-1 levels (juvenile coho, Chinook, chum and a low number of sockeye) are underway and scheduled plans to obtain samples in late June to early July of 2014 are in place

Changes in the diet composition of juvenile sockeye salmon in the Strait of Georgia from the 1960s to the present Changes in the diet composition of juvenile sockeye salmon in the Strait of Georgia from the 1960s to the present

Abstract Studies of the diet of juvenile sockeye salmon in the Strait of Georgia over the past 40 years show a trend of decreasing consumption of copepods and increasing consumption of decapod zooea and larvae. Presently, amphipods and decapods are the dominant prey items on the diet, representing approximately 60% of a relatively restricted number of items. The dominance of decapods in the diet appeared to be unique among the diets of juvenile salmon examined in other studies. Amphipods were usually the most common diet item in all examined studies of juvenile sockeye salmon diets. Studies of the diets of juvenile sockeye salmon, including our own, provide patchy information about a critical period in the establishment of brood year abundance. More comprehensive studies are needed that monitor the diets of juvenile sockeye salmon throughout the early marine period in relation to the composition of their zooplankton prey items

Nearshore and offshore feeding of juvenile salmon and forage fish in the Salish Sea

The Salish Sea provides essential early marine growth environment for several pelagic fish species, including Pacific salmon (Oncorhynchus spp), Pacific herring (Clupea pallasi), and other forage fish (e.g., surf smelt, Hypomesus pretiosus; sand lance, Ammodytes hexapterus). Early marine feeding and growth can be important to survival to adulthood for these species. Early marine growth of Endangered Species Act-listed Puget Sound Chinook salmon (O. tshawytscha) is tightly correlated with smolt to adult returns. Variability in early growth is linked to variation in feeding rate. Therefore, factors which affect feeding success, such as competition, during this life stage could have important influences on marine survival. Recent work has shown spatial-temporal and dietary overlap among juvenile salmon and herring and suggested that potential for competitive interactions exists. However, the extent and strength of potential interactions remain poorly understood and little is known about the feeding of other pelagic planktivores. We describe feeding habits of juvenile salmon, herring, and surf smelt in the Salish Sea to quantify variation in diet composition and characterize dietary overlap. Monthly, yearly, and regional variation was evident, but consistent patterns were distinguishable. During the critical summer growing season, Pacific herring dominated the biomass of the shallow pelagic planktivorous fish community and exhibited extensive diet and spatial overlap with juvenile Chinook salmon and coho salmon (O. kisutch). Crab larvae and amphipods were important prey items. Diet compositions of chum salmon (O. keta) and surf smelt differed from those of the other species, including greater amounts of gelatinous organisms (ctenophores, larvaceans). Our results suggest that assessments of basin carrying capacity and potential species interactions need to account for the population and feeding dynamics of all major daylight planktivores, especially herring

Variability in diet of juvenile Coho and Chinook salmon in the Strait of Georgia during their early marine residence

The Strait of Georgia is an important early marine rearing area for juvenile Pacific Salmon. The linkage of this early marine period to total marine survival has been identified as important but mechanisms regulating the survival during this period have not been identified. This study examines the diet of juvenile Coho and Chinook salmon captured from trawl and purse seine surveys throughout the Strait of Georgia over the past 17 years during the early summer and fall periods. Interannual and regional variations in diet of both species will be assessed to determine if this variation is associated with trends in survival

Juvenile Pacific Herring (Clupea pallasi) and their interactions with ecosystem components in the Strait of Georgia, British Columbia

Pacific Herring (Clupea pallasi) are an important prey species for a variety of predators as well as important to First Nations communities and to the commercial fishing industry. The recruitment of Pacific Herring varies substantially on an annual basis and can represent a large proportion of the adult population biomass, adding uncertainty to population estimates. A leading indicator to forecast their recruitment prior to their harvest would be helpful to understand year class strength. British Columbia’s Strait of Georgia juvenile herring and nearshore pelagic ecosystem survey has collected data from ten core transects in September-October since 1992. This data may help improve the understanding of factors that influence herring recruitment and their availability to their predators, such as Chinook and Coho Salmon. An objective of this study was to update the survey time series of the relative biomass and abundance (and associated variance) of age-0 herring. Results indicate that age-0 herring abundance varies interannually with high abundances in recent, even years and there was an increasing trend in fish condition during 1997-2010. Preliminary results indicate age-0 herring biomass may be a leading indicator of recruitment to the adult herring spawning population and to Chinook Salmon survival. We also explore potential ecological and trophodynamic interactions between herring and ecosystem components, zooplankton abundance, and environmental variability. Investigating the dynamics of ecological linkages among pelagic species will improve our understanding of valuable species in BC’s marine ecosystems