Factors Influencing Avian Predation of Juvenile Upriver Bright Chinook Salmon
To investigate the effects of piscivorous colonial waterbird (avian) predation on juvenile salmonids (smolts; Oncorhynchus spp.) and to determine what proportion of all sources of smolt mortality (1 – survival) were due to avian predation, we conducted a retrospective analysis on Upriver Bright (URB) fall Chinook Salmon (O. tshawytscha) that were marked with Passive Integrated Transponder (PIT) tags and released into the middle Columbia River, USA. We used a state-space Bayesian model that incorporated live detections of tagged fish and recoveries of dead tagged fish on up to 13 different avian colonies to jointly estimate predation and survival probabilities over multiple river-reaches and years (2008 – 2019). Predator species included Caspian Terns (Hydroprogne caspia, hereafter “CATE”), Double-Crested Cormorants (Nannopterum auritum, hereafter “DCCO”), California Gulls (Larus californicus) and Ring-billed Gulls (L. delawarensis, collectively hereafter “LAXX”), and American White Pelicans (Pelecanus erythrorhynchos, hereafter “AWPE”). River-reaches included (1) capture/release from the Hanford Reach for wild-origin smolts or downstream of Priest Rapids Dam for hatchery-origin smolts to McNary Dam, (2) McNary Dam to John Day Dam, (3) John Day Dam to Bonneville Dam, and (4) Bonneville Dam to the Pacific Ocean.
Additional key terms (or species): Hanford, fall chinook, juvenile
Payton, Q., A. Evans, J. Fryer, and T. Garrison. 2021. Factors influencing avian predation of juvenile upriver bright Chinook Salmon. Final Technical Report submitted to the Pacific Salmon Commission Chinook Technical Committee in partial fulfillment of Contract No. 048-001. 36p.