Factors Affecting Migration Timing, Growth, and Survival of Juvenile Coho Salmon in Two Coastal Washington Watersheds

Abstract

Recent improvements in tagging technology allow for the examination of the migration of individual fish, the detection of previously unidentified life histories, and the detailed examination of factors affecting growth, migration, and survival. Using passive integrated transponder tags and instream readers installed near tidewater, we examined the migration, growth, and survival of 18,642 juvenile coho salmon Oncorhynchus kisutch in two small western Washington rivers from 2005 to 2009. In most years, more than 50% of the juvenile coho salmon from a given brood year migrated to sea between 1 October and 31 December (fall migrants). These fall migrants were significantly smaller at tagging than fish that migrated between 1 January and 30 June (spring migrants) but were similar in size to fish that were never detected after tagging and assumed to have died. Annual coho salmon survival estimates from tagging to out‐migration ranged from 31% to 40% for fall and spring migrants combined but from 5% to 15% for spring migrants only. The best fitting regression models indicated that survival differed by river and year and was negatively correlated with tagging location (river kilometer) and positively correlated with fish length: larger fish and those tagged lower in the watershed were more likely to survive. The number of days juvenile coho salmon spent in freshwater before migrating to sea was positively correlated with tagging location, fish length (mm), and habitat depth (m) and negatively with density (coho salmon/m2). Our results suggest that fall or early winter migration is a common life history for juvenile coho salmon that is driven in part by fish size and location in the watershed. The exclusion of fall migrants may lead to underestimates of the total number of migrants and parr‐to‐smolt survival.

Factors Affecting Partial Migration in Puget Sound Coho Salmon

“…Chinook Salmon spend more years at sea, so they might benefit more from the survival advantage than do Coho Salmon, for which rapid growth in marine waters is needed to achieve a large size after only a year and a half at sea (Quinn 2005). It should be noted that all the Coho Salmon in the present study were yearling smolts, but subyearlings can be a substantial fraction of wild populations (Roni et al 2012). Subyearlings would enter marine waters at a much smaller size and different time of year (fall versus spring) than yearling smolts, and it is unclear what proportion of them might become residents in Puget Sound.…”

Watershed-scale effectiveness of floodplain habitat restoration for juvenile coho salmon in the Chilliwack River, British Columbia

“…a Mean of apparent survival and summed proportion survival (which counts fall outmigrants as survivals rather than mortalities; see Roni et al 2012 andHauer 2013).…”

Wood placement in river restoration: fact, fiction, and future direction

“…Salmonids in habitats with abundant wood cover or complex pool habitats move shorter distances than fish in simple habitats with little complexity or wood cover (e.g., Bjornn 1971;Giannico and Hinch 2003;Harvey et al 1999;Heggenes et al 1991;Rinne 1982;Wilzbach 1985). Moreover, recent tagging studies on juvenile salmonid movement have indicated that although most fish do not move long distances during low-flow periods in summer and winter, a portion of juvenile salmonids move long distances or emigrate out of watersheds or subwatersheds in fall or winter (Achord et al 2012;Ibbotson et al 2013;Pess et al 2011;Roni et al 2012).…”