A Review of Factors Affecting the Susceptibility of Juvenile Salmonids to Avian Predation

Abstract

We reviewed studies of piscivorous colonial waterbird predation on juvenile salmonids to synthesize current knowledge of factors affecting fish susceptibility to avian predators. Specifically, we examined peer‐reviewed publications and reports from academic, governmental, and nongovernmental agencies to identify commonalities and differences in susceptibility of salmonids to avian predation, with a focus on mark–recovery studies in the Columbia River basin. Factors hypothesized to influence salmonid susceptibility to avian predation were grouped into four general categories: (1) salmonid species and populations, (2) environmental factors, (3) prey density, predator density, and migration timing, and (4) prey characteristics. Our review focused on predation by Caspian terns Hydroprogne caspia, double‐crested cormorants Nannopterum auritum, and gull species Larus spp. as these are the most well‐studied avian predators of salmonids. Results indicated that predator–prey interactions varied across salmonid species and populations and species of avian predator. Inferences across studies supported multiple hypotheses regarding predator–prey dynamics, including environmental factors that influence prey exposure to predators (e.g., river flows, turbidity, alternative prey), variation in predator and prey abundances, predator characteristics (e.g., foraging behavior, colony location), and prey characteristics (e.g., fish length, condition). Mark–recovery studies of avian predation on fish populations have greatly improved our understanding of the factors affecting fish susceptibility to avian predation, the relative contributions of abiotic and biotic factors to predation susceptibility, and the extent to which avian predation affects fish survival and the viability of prey populations. Future studies that jointly model predation and survival and the factors affecting those processes will further broaden our understanding of predator–prey dynamics and directly evaluate the effects of predation on prey population dynamics.

Fisheries Volume 49 Number 2 February 2024

“…Juvenile steelhead were found to be especially susceptible to predation by Caspian terns nesting on Rice Island, likely due to size-dependent selection (juvenile steelhead are generally larger than other salmonid outmigrants). Also, juvenile steelhead are more surface oriented than other juvenile salmonids during outmigration (Collis et al 2001 ;Hostetter et al 2023 ), a trait that makes them more susceptible to predation by plunge-diving terns.…”

Caspian Tern Management to Increase Survival of Juvenile Salmonids in the Columbia River Basin: Progress and Adaptive Management Considerations

“…2001; Hostetter et al. 2023), a trait that makes them more susceptible to predation by plunge‐diving terns.…”