Using Archival Tags to Infer Habitat Use of Central California Steelhead and Coho Salmon
Sean A. Hayes, Morgan H. Bond, Brian K. Wells, Chad V. Hanson, Andrew W. Jones, R. Bruce MacFarlane
Abstract.—We deployed archival temperature loggers on juvenile and adult coho salmon Oncorhynchus kisutch and steelhead (anadromous rainbow trout) O. mykiss over both the freshwater and marine portions of their lifecycle in order to study their movements and thermal preferences. Beginning in 2003, loggers were deployed on juvenile coho salmon and juvenile and adult steelhead in a small central California coastal stream. A tag recovery from a coho salmon indicates the fish experienced variable temperatures on a daily to weekly basis in the marine environment (mean 13.3°C, range 10–18°C). Tags recovered from steelhead indicate use of a cooler, more stable, thermal habitat window in the marine environment (mean 11.0°C, range 8–14°C), often with little fluctuation over a period of weeks to months, and most thermal changes occurring at the seasonal time scale. Comparisons of steelhead data with sea surface temperature data suggest a northern migration out of the California Current to a narrow band of habitat that fluctuates between the southern boundary of the Bering Sea and north of the 40th parallel. In the shallow freshwater environment, steelhead appeared to be at the mercy of stream temperatures. However, in the estuary, where thermally variable habitats were available, steelhead used a surprisingly broad temperature range, including entering water thought to challenge their thermal tolerances (>20°C) even when cooler waters were available. Temperature loggers recovered on a local beach and island indicate tagged fish were consumed in the estuary by warm-blooded predators. All of these data coupled with a larger number of passive integrated transponder (PIT) tags, are helping to identify discrete habitats fish are using, exact dates of ocean entry and return, and enhance our understanding of marine survival and predation. Finally, archival tags may be useful in understanding habitat use of pelagic long-migrating species like steelhead, by tracking individuals in areas where other tagging technologies are poorly suited.