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UBC Theses and Dissertations

Strategies for coexisting : juvenile pink and chum salmon diets and interactions in a challenging section of coastal migration Zahner (Skil Jaadaa), Vanessa Rose


The cultural and ecological contributions of salmon cannot be understated, as these keystone species have underpinned coastal ecosystems and societies from time immemorial. Despite this millennia-long intimate relationship with Pacific salmon, returns of stocks have become unpredictable and difficult to manage from overfishing and multiple complex stressors. Research has shown that juvenile salmon feeding is a crucial factor for growth and recruitment, and the ocean conditions driving prey availability are tightly coupled with survival of salmon. Pink and chum are abundant co-migratory species of salmon that may exert competitive pressure for food resources during their vulnerable early marine phase. However, competition research on juvenile pink and chum salmon is limited, especially within the complex British Columbia coast. This research aimed to fill gaps in understanding of juvenile pink and chum foraging strategies and interactions in areas of good and poor foraging conditions during their coastal outmigration. In the Discovery Islands and Johnstone Strait regions, there were foraging deserts and oases, where juvenile salmon mean stomach fullness values ranged from < 0.5% to > 6% body weight. In good foraging conditions, juvenile pink and chum both consumed the same high-quality crustacean prey with limited competition, but under poor foraging scenarios, salmon diets differed. Chum salmon consistently consumed gelatinous prey and pink salmon relied more heavily on copepods and nearshore zooplankton, differing in niche in response to competitive interactions. There was a match between predators and prey in 2015, when salmon fed on larger prey, and were in healthier condition (K = 1.0). There was a potential mismatch in 2016, when small prey taxa may have caused poorer condition for juvenile salmon (K = 0.94). Chum salmon had a stronger relationship to prey size than pink, when larger chum successfully consumed the largest prey. These foraging strategies of opportunistic specialization may indeed provide salmon with resilience to face the challenges of shifting climates. Pink and chum salmon can be monitored as indicators for ecosystem health and zooplankton availability. Salmon reflect the health of socio-ecological systems and require our understanding and care to view them holistically as they migrate through diverse, challenging habitats.

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