Spatial and trophic overlap of marked and unmarked Columbia River Basin spring Chinook salmon during early marine residence with implications for competition between hatchery and naturally produced fish

• Published in: Environmental biology of fishes Vol. 94; no. 1; pp. 117 - 134
• Main Authors: Daly, Elizabeth A., Brodeur, Richard D., Fisher, Joseph P., Weitkamp, Laurie A., Teel, David J., Beckman, Brian R.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.05.2012; Springer Nature B.V
• Subjects: Animal behavior; Animal Systematics/Taxonomy/Biogeography; Aquatic ecology; Biomedical and Life Sciences; Coastal waters; Environment; Fish hatcheries; Freshwater & Marine Ecology; Life Sciences; Natural populations; Nature Conservation; Oncorhynchus tshawytscha; River basins; Salmon; Salmonidae; Spatial distribution; Trophic relationships; Zoology; Columbia River; USA, Oregon; USA, Columbia R. basin; INE, USA, Washington; Competition; Marine; Wild; Spatial; Trophic; Juvenile Chinook salmon; Hatchery; Columbia River Basin
• ISSN: 0378-1909; 1573-5133
• DOI: 10.1007/s10641-011-9857-4

Ecological interactions between natural and hatchery juvenile salmon during their early marine residence, a time of high mortality, have received little attention. These interactions may negatively influence survival and hamper the ability of natural populations to recover. We examined the spatial distributions and size differences of both marked (hatchery) and unmarked (a high proportion of which are natural) juvenile Chinook salmon in the coastal waters of Oregon and Washington from May to June 1999–2009. We also explored potential trophic interactions and growth differences between unmarked and marked salmon. Overlap in spatial distribution between these groups was high, although catches of unmarked fish were low compared to those of marked hatchery salmon. Peak catches of hatchery fish occurred in May, while a prolonged migration of small unmarked salmon entered our study area toward the end of June. Hatchery salmon were consistently longer than unmarked Chinook salmon especially by June, but unmarked salmon had significantly greater body condition (based on length-weight residuals) for over half of the May sampling efforts. Both unmarked and marked fish ate similar types and amounts of prey for small (station) and large (month, year) scale comparisons, and feeding intensity and growth were not significantly different between the two groups. There were synchronous interannual fluctuations in catch, length, body condition, feeding intensity, and growth between unmarked and hatchery fish, suggesting that both groups were responding similarly to ocean conditions.