BackgroundHybridization between coastal cutthroat trout (Oncorhynchus clarki clarki) and steelhead or rainbow trout (Oncorhynchus mykiss) has been documented in several streams along the North American west coast. The two species occupy similar freshwater habitats but the anadromous forms differ greatly in the duration of marine residence and migration patterns at sea. Intermediate morphological, physiological, and performance traits have been reported for hybrids but little information has been published comparing the behavior of hybrids to the pure species.Methodology/Principal FindingsThis study used acoustic telemetry to record the movements of 52 cutthroat, 42 steelhead x cutthroat hybrids, and 89 steelhead smolts, all wild, that migrated from Big Beef Creek into Hood Canal (Puget Sound, Washington). Various spatial and temporal metrics were used to compare the behavior of the pure species to their hybrids. Median hybrid residence time, estuary time, and tortuosity values were intermediate compared to the pure species. The median total track distance was greater for hybrids than for either cutthroat or steelhead. At the end of each track, most steelhead (80%) were located near or north of the Hood Canal, as expected for this seaward migrating species, whereas most cutthroat (89%) were within 8 kilometers of the estuary. Most hybrids (70%) were detected leaving Hood Canal, though a substantial percentage (20%) remained near the Big Beef Creek estuary. More hybrids (7.5%) than pure cutthroat (4.5%) or steelhead (0.0%) were last detected in the southern reaches of Hood Canal.Conclusions/SignificanceGiven the similarity in freshwater ecology between the species, differences in marine ecology may play an important role in maintaining species integrity in areas of sympatry.
Results from a 4‐year tagging study of the migration behavior of Pacific salmon smolts indicate an effect of lunar gravitation on the time of saltwater entry at an artificial tidal barrier. We used passive integrated transponders to tag several populations of juvenile Chinook salmon Oncorhynchus tshawytscha, coho salmon O. kisutch, and sockeye salmon O. nerka, including hatchery and wild Chinook salmon. We discovered through exploratory data analyses that the temporal variation in the date of initiation of passage at the barrier by the majority of the Chinook salmon populations studied was most closely related to the date of lunar apogee, followed by the date of quarter moon. Both phenomena are associated with weaker net lunar gravitation effects on water bodies than the full or new moon, which showed no consistent effect. Using available data we could not discern any effect of other environmental variables, including water temperature, nocturnal illumination, salinity, and lake level. Lunar apogee occurred on average 1 d prior to the onset of substantial passage by Chinook salmon smolts. The phenomenon was consistent in all 4 years, even though the lunar apogee cycle advanced annually by 7 d. An intermediate relationship was noted for coho salmon smolts and the weakest relationship for sockeye salmon smolts.
Partial migration, a term referring to populations in which only a fraction of the individuals migrate, is a widespread phenomenon among fishes. However, it is not always clear whether there are only two alternatives (migration or residency) or a continuum of movement patterns. For example, Coho Salmon Oncorhynchus kisutch are anadromous, and most individuals rear over the continental shelf or in offshore waters of the North Pacific Ocean; however, some Coho Salmon (known as residents) spend all or part of their marine lives within Puget Sound. The movements of residents are poorly documented, and it is unclear whether they ever leave Puget Sound and move to the coast of Washington and to what extent they move within Puget Sound. Accordingly, the goal of this study was to investigate the patterns of movement by immature Coho Salmon in Puget Sound at a series of spatial scales. We tagged 45 resident Coho Salmon in the central basin of Puget Sound with acoustic transmitters and detected their movements with fixed receivers in the Salish Sea. Seven individuals were detected as departing Puget Sound through the Strait of Juan de Fuca, but these fish did not differ in body size, origin (wild or hatchery), or tagging date from fish that remained in Puget Sound. The fish remaining as residents seldom moved between the marine basins of Puget Sound. Within the central basin, deeper/offshore sites had higher frequencies of detection and other indices of site use. Fish were more often present and moved more often at shallow sites close to shore during the night, whereas they were more often present and moved more at deep, offshore sites during the day. We suggest that rather than being a discrete behavior, residence in Puget Sound by Coho Salmon is part of a continuum of migratory behavior patterns.
Wild, downstream-migrating cutthroat trout, Oncorhynchus clarkii clarkii, smolts and adults were captured at a weir in Big Beef Creek, Hood Canal, Washington, surgically implanted with acoustic tags and tracked to identify spring and summer movements using stationary receivers in order to test the assumption that the species moves little while in marine waters. Overall, 93-96% migrated from the stream into the east side of the long narrow fjord, where they dispersed north and south along the shoreline. Most O. c. clarkii were detected nearshore within 10 km of the release site, with declining detection rates to 77 km. Over one-third (36%) crossed c. 2-4 km of deep water to the other side but only one O. c. clarkii left the Hood Canal basin. Movements and behaviour patterns did not differ between smolts and adults but cluster analysis revealed two modes of distribution, here categorized as residents and migrants. Within these categories of overall distribution, a range of finer-scale behaviour patterns was observed, including sedentary individuals, daily moving between proximate sites and more continuous long-distance travel. Diel movement patterns varied markedly among individuals but overall activity increased near dawn, peaked around mid-day and declined but continued at night. These patterns contrast with sympatric and closely related steelhead trout, Oncorhynchus mykiss, providing new insights into the diversity of salmonid behaviour.
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