Oncorhynchus nerka (ALASKA COASTAL DOWNWELLING, EASTERN GULF OF ALASKA)
|Scientific Name:||Oncorhynchus nerka (ALASKA COASTAL DOWNWELLING, EASTERN GULF OF ALASKA)|
|Species Authority:||(Walbaum, 1792)|
|Taxonomic Notes:||A total of 93 extant and five extinct subpopulations were identified across the natural range of O. nerka. The assessors used a combination of ecoregional information (i.e., based on differences in marine and freshwater habitat) and the degree of genetic divergence between known spawning locations, using an Fst value of 0.04, representing a threshold level of gene flow between putative subpopulations of less than or equal to one effective migrant per year. The five extinct subpopulations were based on Gustafson et al. 2007. While the assessors acknowledge that it is not straightforward to ascribe demographic or geographic distinctness to a subpopulation based on observed genetic distances, they feel it is the most appropriate methodology given the scale of the assessment and the paucity of observations of stray rates among the spawning locations considered in this assessment. For the amendment completed in 2011, we split a number of British Columbia subpopulations described in the original 2008 assessment based on additional input from experts. For a complete description of the approach and methods used for identifying units and the underlying assumptions, please refer to the supplementary material
Subpopulation naming convention:
Subpopulation names consist of an ecoregion name in upper case with any subdivision of the ecoregion by other criteria (e.g. genetic divergence) indicated in proper case after a colon.
|Red List Category & Criteria:||Vulnerable A2a ver 3.1|
|Reviewer(s):||Ruggerone, G. & English, K.|
This subpopulation was evaluated against relevant A, B and D criteria. Recent escapement trends at individual monitoring sites were analyzed and results were scaled upwards to characterize the Red List status of the subpopulation against A2 criterion (i.e., based on the rate of change in adult abundance over three generations, or 12 years for this species). The rate of change applied to this subpopulation, assessed over 6 site(s), was -39%. It therefore qualifies as Vulnerable against criterion A2. For evaluation against B2 criterion, we estimated the area of occupancy and the number of extant locations for the subpopulation. Area of occupancy was estimated on a one kilometer square grid overlaid on the nursery lake(s) and freshwater river habitat. This surface area estimate is meant to capture habitat occupied for spawning and rearing by both lake- and river-type life histories. The number of extant locations was the sum of the total number of known nursery lakes and distinct spawning regions supporting the subpopulation. The surface area of freshwater habitat supporting this subpopulation (864 km2), the number of extant locations (>35 lakes and/or distinct spawning areas), and its observed rate of change in adult abundance described above qualifies this subpopulation as Least Concern against the B2ab(v) criteria. The current abundance of mature adults in the subpopulation qualifies it as Least Concern against the D1 criterion. See the supplementary material for data sources, trend model parameters and complete description of methods and assumptions.
|Previously published Red List assessments:|
|Range Description:||The current distribution of Oncorhynchus nerka extends from approximately 45-70°N to 140°E-125°W longitude. The species has been recorded from Russia, United States, Canada, and Japan, although the Japanese populations are likely to have resulted from introductions; Japan is therefore not considered to be part of this species' natural range. |
See the supplementary material (particularly Figures 1 & 2, and Appendices 1 & 2) for details on the range of this species and of each of the 98 subpopulations identified.
Native:United States (Alaska)
|FAO Marine Fishing Areas:|
Pacific – northeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||At the species level, the population is believed to be stable; however, some subpopulations are declining. For more details on subpopulation size estimates and trends, see the supplementary material (particularly Appendix 2).|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||The species exhibits a great variety of life history patterns. It has a genetically diverged life history form called “kokanee” that lives its entire life within freshwater, but this assessment includes only anadromous populations commonly referred to as “sockeye” or “red salmon”. Sockeye are born in gravel nests in rivers or lakes and the majority of life history forms rear as juveniles for one to three years in freshwater before migrating to the ocean. Some sockeye assume a river-type life history and rear in a river channel, while others are lake-type and rear in a lake environment. Primary prey during this life history stage include zooplankton and stream invertebrates. Some sea-type populations migrate within one to three months following emergence, and these make extensive use of estuaries. Most populations spend one to three years in offshore feeding areas where they grow to maturity (ca. 50-60 cm total length, 2.5-3.0 kg weight). Diet in the ocean consists primarily of zooplankton (copepods and euphausiids), but their diet also includes squids and fishes. Natural predators during this period in their life history include salmon sharks (Lamna ditropis) and Daggertooth (Anotopterus nikparini). Foraging individuals mix among populations both within and between Asia and North America, but at maturity they all migrate back toward their natal freshwater habitat where they spawn and die. The return to natal habitat and the isolation of spawning populations results in considerable genetic differentiation and adaptation to local conditions. Many fish are intercepted by fishers during the homeward, spawning migration, and natural predators include seals, sea lions and bears. Spawning occurs in late summer and autumn, in lake outlet or lake tributary streams or along lake beaches in finer sediments where subterranean upwelling occurs or among boulders on wave-aerated shores. River-type sockeye spawn in river channels not associated with lakes. Adults display bright red bodies and green heads. Males compete with each other for access to females. Females compete with each other for gravel sites where they build nests, deposit eggs (fecundity typically ranges from 2,000-5,000 eggs), and briefly guard the redd. Median population size for the species is ca. 6,000 individuals. Reviews of life history and ecology of the species appear in Smith et al. (1987), Burgner (1991), Wood (1995) and Quinn (2005).|
|Movement patterns:||Full Migrant|
|Use and Trade:||A certain percentage of sockeye are captured and killed exclusively for their roe (eggs, caviar). This occurs primarily in the Russian portion of their natural range, and the fishery is illegal and the take is unreported.|
General threats to O. nerka
The key threats to the species identified by the IUCN SSC Salmon Specialist Group were:
a) Mixed stock fishing leading to over fishing small, less productive populations
b) Changing river and ocean conditions that are likely linked to global climate change, expressed in poor marine survival rates and increased incidence of disease in adult spawners
c) Negative effects of hatcheries and construction of artificial spawning habitat
It is important to note that in many cases, the causes for declines in some specific sockeye salmon subpopulations remain unknown.
Many subpopulations of sockeye in
Most of the data used in our assessment, particularly in
4. Mixed-stock fishing is likely to be a key factor in the decline observed at many sites and subpopulations in our assessment. We feel a key priority is filling a gap in knowledge about composition of mixed-stock harvest in coastal sockeye salmon fisheries. While a great deal of resources has been invested in developing weak-stock management for Fraser River sockeye salmon through the Pacific Salmon Commission and DFO, there has been much less attention placed in other regions along the west coast of North America, particularly in the regions where we found the greatest diversity of subpopulations. We encourage continued investment in developing methods and protocols to account for subpopulation composition of coastal fisheries targeting sockeye salmon to help track harvest pressure at a biologically and ecologically meaningful scale. Further, we encourage fisheries management agencies to explore restructuring fisheries in a way that would result in shifting fishing pressure from coastal regions to more terminal locations, thus providing a more effective means of controlling fishing pressure at the scale of individual subpopulations.
Another leading factor threatening sockeye salmon are poor marine survival
rates. This has been documented in cases where smolt-to-adult survival rates
are estimated through intensive monitoring programs. This appears to be a
significant factor explaining declines in adult abundance across many locations
in the southern range of the species in
Many previous attempts at re-introductions of sockeye salmon have been
unsuccessful, and we feel any effort at captive breeding or inter-basin
transfers for re-introduction purposes should proceed with great caution. These
efforts, to the extent that they exist, are at best stop-gap measures and are
in no way a substitute for conserving the species in the wild. The lack of
success from the captive breeding of endangered Sakinaw sockeye salmon by DFO,
Enhancement activities (particularly hatchery releases and spawning channel
construction) is likely to be a key factor in reducing abundance in
neighboring, small wild populations. In our assessment, we were unable to
functionally track both wild and enhanced sockeye salmon where they
intermingle. We strongly recommend adoption of integrated monitoring programs
that includes a robust marking program and monitoring efforts targeted toward
wild sockeye salmon populations that would provide the data necessary to
address the degree to which enhancement practices threaten wild sockeye salmon.
It is important to note that two large basins in our assessment (Fraser and
8. While not addressed in the present assessment due to lack of data, we feel there should be more focused research attention on sea-and river-type sockeye that may serve as colonizers in the future. This line of research is particularly important given expected habitat alterations from climate change.
9. Very few data were available to assess population viability of sockeye salmon in the Russian Far East, and we document a significant reduction in escapement in recent years at a site within the
|Citation:||Rand, P.S. 2011. Oncorhynchus nerka (ALASKA COASTAL DOWNWELLING, EASTERN GULF OF ALASKA). The IUCN Red List of Threatened Species 2011: e.T135322A4084933.Downloaded on 30 August 2016.|
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