title: Inter-Tributary Movements by Resident Salmonids across a Boreal Riverscape.
abstract: Stream-dwelling fishes inhabit river networks where resources are distributed heterogeneously across space and time. Current theory emphasizes that fishes often perform large-scale movements among habitat patches for reproduction and seeking refugia, but assumes that fish are relatively sedentary during growth phases of their life cycle. Using stationary passive integrated transponder (PIT)-tag antennas and snorkel surveys, we assessed the individual and population level movement patterns of two species of fish across a network of tributaries within the Wood River basin in southwestern Alaska where summer foraging opportunities vary substantially among streams, seasons, and years. Across two years, Arctic grayling (Thymallus arcticus) and rainbow trout (Oncorhynchus mykiss) exhibited kilometer-scale movements among streams during the summer growing season. Although we monitored movements at a small fraction of all tributaries used by grayling and rainbow trout, approximately 50% of individuals moved among two or more streams separated by at least 7 km within a single summer. Movements were concentrated in June and July, and subsided by early August. The decline in movements coincided with spawning by anadromous sockeye salmon, which offer a high-quality resource pulse of food to resident species. Inter-stream movements may represent prospecting behavior as individuals seek out the most profitable foraging opportunities that are patchily distributed across space and time. Our results highlight that large-scale movements may not only be necessary for individuals to fulfill their life-cycle, but also to exploit heterogeneously spaced trophic resources. Therefore, habitat fragmentation and homogenization may have strong, but currently undescribed, ecological effects on the access to critical food resources in stream-dwelling fish populations.
authors.affiliation: School of Aquatic and Fishery Sciences, Box 355020, University of Washington, Seattle, Washington, United States of America.
authors.forename: Kale T
authors.initials: KT
authors.lastname: Bentley
authors.affiliation: School of Aquatic and Fishery Sciences, Box 355020, University of Washington, Seattle, Washington, United States of America.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Schindler
authors.affiliation: School of Aquatic and Fishery Sciences, Box 355020, University of Washington, Seattle, Washington, United States of America; Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming, United States of America.
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Armstrong
authors.affiliation: School of Aquatic and Fishery Sciences, Box 355020, University of Washington, Seattle, Washington, United States of America.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Cline
authors.affiliation: Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle, Washington, United States of America.
authors.forename: Gabriel T
authors.initials: GT
authors.lastname: Brooks
mesh_terms: D000413:Alaska; D025041:Animal Migration; D000818:Animals; D009068:Movement; D017686:Oncorhynchus mykiss / Q000254:growth & development / Q000502:physiology*; D045483:Rivers; D012621:Seasons; D016019:Survival Analysis