Dataset Information

In situ measurement of coastal ocean movements and survival of juvenile Pacific salmon.

ABSTRACT: Many salmon populations in both the Pacific and Atlantic Oceans have experienced sharply decreasing returns and high ocean mortality in the past two decades, with some populations facing extirpation if current marine survival trends continue. Our inability to monitor the movements of marine fish or to directly measure their survival precludes experimental tests of theories concerning the factors regulating fish populations, and thus limits scientific advance in many aspects of fisheries management and conservation. Here we report a large-scale synthesis of survival and movement rates of free-ranging juvenile salmon across four species, 13 river watersheds, and 44 release groups of salmon smolts (>3,500 fish tagged in total) in rivers and coastal ocean waters, including an assessment of where mortality predominantly occurs during the juvenile migration. Of particular importance, our data indicate that, over the size range of smolts tagged, (i) smolt survival was not strongly related to size at release, (ii) tag burden did not appear to strongly reduce the survival of smaller animals, and (iii) for at least some populations, substantial mortality occurred much later in the migration and more distant from the river of origin than generally expected. Our findings thus have implications for determining where effort should be invested to improve the accuracy of salmon forecasting, to understand the mechanisms driving salmon declines, and to predict the impact of climate change on salmon stocks.

SUBMITTER: Welch DW

PROVIDER: S-EPMC3102360 | biostudies-literature | 2011 May

REPOSITORIES: biostudies-literature

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In situ measurement of coastal ocean movements and survival of juvenile Pacific salmon.

Welch David W DW Melnychuk Michael C MC Payne John C JC Rechisky Erin L EL Porter Aswea D AD Jackson George D GD Ward Bruce R BR Vincent Stephen P SP Wood Chris C CC Semmens Jayson J

Proceedings of the National Academy of Sciences of the United States of America 20110510 21

Many salmon populations in both the Pacific and Atlantic Oceans have experienced sharply decreasing returns and high ocean mortality in the past two decades, with some populations facing extirpation if current marine survival trends continue. Our inability to monitor the movements of marine fish or to directly measure their survival precludes experimental tests of theories concerning the factors regulating fish populations, and thus limits scientific advance in many aspects of fisheries manageme ...[more]

PMID: 21558442

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Project description:The long-term viability of Pacific salmon stocks and the fisheries they support are threatened if large numbers die prematurely en-route to spawning grounds. Physiological profiles that were correlated with the fate of wild sockeye salmon during river migration were discovered using functional genomics studies on biopsied tissues. Three independent biotelemetry studies tracked the biopsied fish after tagging in the marine environment over 200 km from the Fraser River, in the lower river 69 km from the river mouth and at the spawning grounds. Salmon carrying the poor performance (unhealthy) profile in the ocean exhibited a 4-times lower probability of arriving to spawning grounds than those with a healthy genomic signature, although generally migrated into the river and to the spawning grounds faster. A related unhealthy signature observed in the river was associated with a 30% reduction in survival to spawning grounds in one of the three stocks tested. At spawning grounds, the same poor performance signature was associated with twice the pre-spawning mortality compared with healthy fish. Functional analysis revealed that the unhealthy signature, which intensified during migration to spawning grounds, was consistent with an intracellular pathogenic infection, likely a virus. These results are the first to suggest a pathogen present in salmon in the marine environment could be a major source of mortality during migration and spawning in the river. This series is of gill expression profiles from the study of fish sampled and tagged in the ocean and tracked as they entered the river system and swam towards the spawning grounds. Fish were caught in seine nets, gastrically implanted with radio transmitters, and biopsy sampled for blood, gill, muscle, and fin. Individual fish were tracked by receivers placed throughout the Fraser River watershed to identify and fate (i.e. the location of the receiver that last detected the fish). Targeted stocks of interest were genetically identified. Gene expression was profiled in gill tissue, a critical respiratory and ionoregulatory organ that is highly responsive to stress, chemical exposure and disease. Gene expression was assayed on the GRASP salmonid 16K cDNA microarray.

Project description:BACKGROUND: Migrations allow animals to find food resources, rearing habitats, or mates, but often impose considerable predation risk. Several behavioural strategies may reduce this risk, including faster travel speed and taking routes with shorter total distance. Descriptions of the natural range of variation in migration strategies among individuals and populations is necessary before the ecological consequences of such variation can be established. METHODOLOGY/PRINCIPAL FINDINGS: Movements of tagged juvenile coho, steelhead, sockeye, and Chinook salmon were quantified using a large-scale acoustic tracking array in southern British Columbia, Canada. Smolts from 13 watersheds (49 watershed/species/year combinations) were tagged between 2004-2008 and combined into a mixed-effects model analysis of travel speed. During the downstream migration, steelhead were slower on average than other species, possibly related to freshwater residualization. During the migration through the Strait of Georgia, coho were slower than steelhead and sockeye, likely related to some degree of inshore summer residency. Hatchery-reared smolts were slower than wild smolts during the downstream migration, but after ocean entry, average speeds were similar. In small rivers, downstream travel speed increased with body length, but in the larger Fraser River and during the coastal migration, average speed was independent of body length. Smolts leaving rivers located towards the northern end of the Strait of Georgia ecosystem migrated strictly northwards after ocean entry, but those from rivers towards the southern end displayed split-route migration patterns within populations, with some moving southward. CONCLUSIONS/SIGNIFICANCE: Our results reveal a tremendous diversity of behavioural migration strategies used by juvenile salmon, across species, rearing histories, and habitats, as well as within individual populations. During the downstream migration, factors that had strong effects on travel speeds included species, wild or hatchery-rearing history, watershed size and, in smaller rivers, body length. During the coastal migration, travel speeds were only strongly affected by species differences.

Dataset Information

In situ measurement of coastal ocean movements and survival of juvenile Pacific salmon.

Publications

In situ measurement of coastal ocean movements and survival of juvenile Pacific salmon.

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