Why do Salmon Stray? Tradeoffs Between Habitat and Homing

Abstract

Salmon are capable of precise homing at fine spatial scales, but some proportion of them stray to other areas within their natal system for spawning. Hatchery supplementation programs, such as the one being used in the Yakima River, WA, create an ideal system in which to study the tradeoffs between homing and habitat. Hatchery-origin fish are reared in acclimation facilities that are intended to extend the spatial distribution of spawning and increase natural production. The objectives of this study are to (1) quantify habitat differences among acclimation areas, (2) evaluate spatial patterns of spawning by hatchery- and wild-origin Chinook salmon, (3) identify physical habitat characteristics are associated with straying behavior among hatchery-origin females, and (4) determine the scale at which straying occurs from each acclimation area. Extensive surveys of channel morphology and physical habitat were conducted in over 160 km of mainstem, floodplain, and tributary river habitat in 2007. Preliminary results suggest that acclimation areas differ significantly in habitat characteristics across spatial scales (250 m, 1 km, 8 km, and 15 km). Hatchery-origin females select spawning sites that are away from acclimation areas and are characterized by deep, upstream habitat types. Multiple channel, glide, and pool habitats were associated with high density spawning at the 1 km scale.