Patterns of homing and straying in southern British Columbia coded-wire tagged chinook salmon ( Oncorhynchus tshawytscha) populations

Abstract

Chinook salmon ( Oncorhynchus tshawytscha) reared in a hatchery can originate from the same river on which a hatchery is located (natal river) or from a foreign river. Non-displacement rearing occurs if juveniles originating from the same drainage as the hatchery are released back into the natal stream. Displacement rearing occurs if part of the rearing and release strategy occurs at a foreign drainage or includes the marine environment. We compared straying between non-displacement and three types of displacement releases where: (1) juveniles are transported, reared in a central hatchery and released back into natal drainage (satellite); (2) or transported, reared in a central or recipient hatchery and released in a foreign drainage (transplant); (3) or reared and released directly into the marine environment away from the home drainage (out-estuary). Compared with non-displacement rearing, displacement-reared fish were between two and five times more likely to stray (2.1–5.3% vs 1.2%). Out-estuary releases had the highest stray rates of the displacement rearing types and were suspected of being least successful at imprinting on the home stream. Analysis of hybrid and transplanted stocks suggested that there was a genetic component to homing. A hybrid stock was three times more likely to stray than the natal stock released at the same time and location (6.2% vs 2.4%). Transplanted fish without exposure to their ancestral drainage were more likely to stray back to the ancestral drainage than non-transplanted fish released at the same time and location (2.9% vs 0.1%). Approximately 50% of the stray migrants were recovered within 30 km of the release site, indicating that the highest risk of straying may occur during the transition from bi-coordinate navigation to imprinted natal stream clues.