Sockeye Salmon Abundance Research Articles

Biological and environmental covariates of juvenile sockeye salmon distribution and abundance in the southeastern Bering Sea, 2002-2018.

Climate change is altering the distribution and abundance of marine species, especially in Arctic and sub-Arctic regions. In the eastern Bering Sea, home of the world's largest run of sockeye salmon (Oncorhynchus nerka), juvenile sockeye salmon abundance has increased and their migration path shifted north with warming, 2002-2018. The reasons for these changes are poorly understood. For these sockeye salmon, we quantify environmental and biological covariate effects within spatio-temporal species distribution models. Spatio-temporally, with respect to juvenile sockeye salmon densities: (1) sea surface temperature had a nonlinear effect, (2) large copepod, Calanus, a minor prey item, had no effect, (3) age-0 pollock (Gadus chalcogrammus), a major prey item during warm years, had a positive linear effect, and (4) juvenile pink salmon (O. gorbuscha) had a positive linear effect. Temporally, annual biomass of juvenile sockeye salmon was nonlinearly related to sea temperature and positively related to age-0 pollock and juvenile pink salmon abundance. Results indicate that sockeye salmon distributed with and increased in abundance with increases in prey, and reached a threshold for optimal temperatures in the eastern Bering Sea. Changes in population dynamics and distribution of sockeye salmon in response to environmental variability have potential implications for projecting specific future food securities and management of fisheries in Arctic waters.

Biennial patterns in Alaskan sockeye salmon ocean growth are associated with pink salmon abundance in the Gulf of Alaska and the Bering Sea

Abstract In response to ocean heating and hatchery production, pink salmon (Oncorhynchus gorbuscha) returning from the North Pacific Ocean steadily increased after 1975, leading to concerns about their influence on food webs and competition with other species. Using measurements of distance between scale annuli of 24 584 individual sockeye salmon (O. nerka), we examined growth during their 2 or 3 years at sea from 1977 to 2015 for eight populations in Alaska. We found significant, negative autocorrelations at 1 lag year in annual growth of sockeye salmon, with a consistent pattern of lower growth in odd years, i.e. opposite to the biennial pattern of pink salmon abundance. Peak pink salmon abundances reduced growth of sockeye salmon from 7 to 14% during the second year in the ocean compared with growth when pink salmon abundance was low, while third-year growth was reduced up to 17%. The overall effect of pink salmon abundance on sockeye growth was over two times greater than the effect of sockeye salmon abundance. Production hatcheries and ocean heating contribute to the competitive dominance of pink salmon, underscoring the need to consider this unintended anthropogenic effect on the growth and productivity of sockeye salmon throughout the North Pacific.

Analysis of state for the stocks of sockeye salmon ((<i>Oncorhynchus nerka</i>) from the Bolshaya River (western Kamchatka) in 1929–2022

The spawning stock of sockeye salmon in the Bolshaya River is evaluated for 1929–2022. Long-term tendencies are determined for their most important biological parameters, in particular, a juvenilization of returning spawners with decreasing of their body size, weight, and fecundity. Possible causes of these processes are considered. Biological indices of the sockeye salmon belonged to different races, ecological forms, ecotypes, and genders are compared statistically for different periods of time, with the frequency analysis. Changes in the size and age structure are revealed — range of the size and age variability has decreased. The age structure in the sea adjacent to the Bolshaya River mouth contradicts the hypothesis of a significant portion of sockeye salmon from Lake Kurilskoye in seine by-catch. The sockeye salmon abundance has changed periodically and recently is at the top of the wave. Compared to the 1929–2000 average, the stock has increased 6–7 times by 2020, and more than tenfold in 2022, whereas the average multiplicity of reproduction has increased 9 times (such a high value is obviously due to underestimation of spawning).

Sockeye salmon of Russian origin: what can fishermen сount on?

Information on dynamics of abundance for sockeye salmon of Russian origin is presented, with assumptions on prospects of this species fishery in the future decade. The average annual catch in the period from 1907 to 2022 was about 27 thousand tons. The abundance of Asian sockeye salmon decreased twice (before 1927 and in 1965–2001) and increased twice (in 1928–1964 and since 2002 to the present) for 35–37 years. So, the stock fluctuated with the period about 70–75 years. This dynamics of sockeye salmon abundance is very similar to changes in the stocks of other pacific salmon species of Russian origin; in particular, the annual catches of sockeye salmon correlate closely with the landing of pink salmon and chum salmon in 1971–2022. Taking into account these regularities, prospects of sockeye salmon fishery in the Russian waters are estimated. High values of the annual catch, no less than 35 . 103 t, are expected until late 2020s — early 2030s.

Links between fluctuations in sockeye salmon abundance and riparian forest productivity identified by remote sensing

AbstractPacific salmon (Oncorhynchus spp.) carcasses can fertilize riparian forests with marine‐derived nutrients when populations make their annual return to natal streams to spawn; however, the strength of this cross‐system linkage likely varies substantially among years due to the interannual fluctuations in abundance that characterize most salmon populations. Here, we used a 36‐yr time series (1984–2019) of satellite imagery and salmon abundance estimates to assess spatiotemporal associations between forest greenness (a measure of plant productivity) and adult sockeye salmon (Oncorhynchus nerka) abundance in the lower Adams River, British Columbia, Canada. The Adams River sockeye population displays a quadrennial pattern of abundance, with a dominant cohort that spawns every four years in numbers that are typically two to three orders of magnitude larger than non‐dominant cohorts. We found that variation in forest greenness was consistently explained best by models including dominant cohort year, whereas models lacking an index of salmon abundance were the lowest‐ranked. Greenness of riparian vegetation increased by an average of 0.015 NDVI units (approximately 1%) in the summer after a dominant cohort return, and this effect on greenness persisted into the subsequent fall (11–13 months after spawning). The positive association between quadrennial pulses of salmon and riparian greenness occurred in plots both within 30 m of the stream and 95–125 m away from the stream, indicating that the spatial extent of fertilization may occur well beyond areas directly adjacent to the riverbank. These results suggest that forests respond to cyclical variation in salmon abundance and that overwinter storage of marine‐derived nutrients within catchments allows plants to capitalize on these nutrients in the following growing season. Continued advances in remote sensing technology will enhance our understanding of cross‐system resource linkages and can inform the ecosystem‐based management of Pacific salmon.

Estuary habitat associations for juvenile Pacific salmon and pelagic fish: Implications for coastal planning processes

Abstract Assessment of risk from industrial developments often relies on simple habitat descriptions for focal species. However, simple habitat metrics may not be accurate predictors of locations that species actually use. Understanding the nature of habitat is particularly pressing for estuaries, as they are among the most degraded ecosystems globally but provide critical rearing habitat for many species, including Pacific salmon. Canadian environmental impact assessment approaches use simple habitat‐type models to assess risk from developments and assume that different species of salmon rely on the same habitat. This study asked what combination of habitat type and biophysical covariates best predicted use of estuary habitat by juvenile salmon and two dominant small pelagic fish. Fish were sampled via purse seine throughout the Skeena River estuary (British Columbia, Canada) for 2 years across different habitat types (eelgrass, open water, sandy banks, and rocky shores). Simple habitat‐type models were compared with models with more complex biophysical variables to predict the variability in relative abundance of juvenile Chinook (Oncorhynchus tshawytscha), coho (Oncorhynchus kisutch), and sockeye (Oncorhynchus nerka) salmon, along with pelagic fish species Pacific herring (Clupea pallasii) and surf smelt (Hypomesus pretiosus). The combination of variables that best predicted abundance differed across fish species. Pelagic fish were associated with near‐shore sites, increased temperature (herring), and increased salinity (smelt). Juvenile coho and sockeye salmon (but not Chinook), were more abundant in higher turbid waters. Chinook and sockeye salmon used eelgrass habitat more frequently than other habitat types, whereas coho salmon were more abundant in areas with high macroalgae cover. Models with these variables had greater predictive power than those using habitat type alone for juvenile salmon. Simple classifications of estuary habitat currently used in environmental risk assessment may not reflect the complex nature of fish–habitat associations. Understanding biophysical factors associated with estuary fish abundance can inform management of estuary habitat to support their nursery function for important fish.

Modelling salmon migration as a mixture problem

Pulses of abundance in salmon migrations can arise from single populations arriving at different times, from multiple populations with different timing characteristics, or as a combination of these. Daily observations typically record an aggregate measure of abundance passing some location rather than the abundances of the individual components. An objective method is described that partitions a compound migration into its component parts by exploiting differences in the characteristics of each pulse. Simulated data were used to demonstrate when greater model complexity may be desirable. Three case studies of increasing complexity (Chilko Lake sockeye salmon smolts (Oncorhynchus nerka), large adult Columbia River Chinook salmon (Oncorhynchus tshawytscha), Fraser River salmon test fishery) demonstrate how the model can be applied in practice. Results indicated that Chilko Lake smolts rarely emigrate to sea as a single pulse, that the dates used to distinguish the spring run of Chinook salmon in the Columbia River may be overestimating its abundance, and that pulses of sockeye salmon abundance in a Fraser River ocean test fishery in 2014 may have arisen from some factor other than population composition.

Sockeye salmon population dynamics over the past 4000\xa0years in Upper Russian Lake, south-central Alaska

Stable nitrogen isotope (δ15N) data from sediment cores taken in clear-water Upper Russian Lake (Kenai River Watershed, Alaska, USA) indicate that sockeye salmon (Oncorhynchus nerka) populations varied significantly over the past 4000 years, with a prominent ~ 650-year period of lower salmon abundance from ~ 100 BCE to 550 CE. Sediment characteristics during this ~ 650-year interval reflect glacial sediment input, which may have contributed to the salmon decline by degrading spawning habitat and reducing carrying capacity. The decline, however, coincides with large reductions in sockeye salmon abundance identified previously in Karluk and Akalura lakes on Kodiak Island, > 400 km southwest, supporting the possibility of regionally synchronous, multi-centennial production regimes that may originate from shifts in oceanographic conditions such as biological productivity in the northeastern Pacific Ocean. Under such a scenario, coincidence with watershed glacial activity indicates a common driver, i.e. regional climate change. Climate conditions that led to significant glacial advances in this part of the Kenai Peninsula (cold and/or wet conditions) may have also created unfavorable ocean conditions during critical periods in the marine phase for these stocks of Gulf of Alaska sockeye salmon. Future climate projections and management strategies should focus on how climate regimes impact not only prey availability for salmon at sea, but also local conditions for spawners and juveniles.

The change in water circulation and its implication for the distribution and abundance of salmon in the western Bering Sea in the early 21st century

A “change” in water circulation took place in the Bering Sea in 2007. The Bering Sea cyclonic gyre decreased to the size of the Commander Basin; the longitudinal northward flow from the Near Strait intensified, and the latitudinal westward flow from the Aleutian Basin along the Koryak coast and the Bering Slope Current became noticeably weaker. The longitudinal flow formed a hydrodynamic front along the border of the Russian EEZ that prevented cold subsurface waters from spreading eastward. The changes in circulation of waters that were observed in the Bering Sea during the 2007–2011 period, as compared to the situation in 2002–2006, had an influence on the intensity of feeding migrations of immature salmon into Russian waters. The abundance of immature chum, sockeye, and chinook salmon in the western part of the sea declined and the pattern of their spatial distribution was altered. In 2012, after the water circulation changed to its original pattern, the abundance of salmon was restored to the levels that were recorded in 2002–2006.

Productivity and life history of sockeye salmon in relation to competition with pink and sockeye salmon in the North Pacific Ocean

Sockeye salmon (Oncorhynchus nerka) populations from Southeast Alaska through British Columbia to Washington State have experienced similar declines in productivity over the past two decades, leading to economic and ecosystem concerns. Because the declines have spanned a wide geographic area, the primary mechanisms driving them likely operate at a large, multiregional scale at sea. However, identification of such mechanisms has remained elusive. Using hierarchical models of stock–recruitment dynamics, we tested the hypothesis that competition between pink (Oncorhynchus gorbuscha) and sockeye salmon for prey has led to reduced growth and productivity and delayed maturation of up to 36 sockeye populations spanning the region during the past 55 years. Our findings indicate the abundance of North Pacific pink salmon in the second year of sockeye life at sea is a key factor contributing to the decline of sockeye salmon productivity, including sockeye in the Fraser River where an increase from 200 to 400 million pink salmon is predicted to reduce sockeye recruitment by 39%. Additionally, length-at-age of Fraser River sockeye salmon declined with greater sockeye and pink salmon abundance, and age at maturity increased with greater pink salmon abundance. Our analyses provide evidence that interspecific competition for prey can affect growth, age, and survival of sockeye salmon at sea.

Reliable Identification of Declining Populations in an Uncertain World

AbstractAssessments of extinction risk based on population declines are widely used, yet scientists have little quantitative understanding of their reliability. Incorrectly classifying whether a population is declining or not can lead to inappropriate conservation actions or management measures, with potentially profound societal costs. Here we evaluate key causes of misclassification of decline status and assess the reliability of 20 decline metrics using a stochastic model to simulate time series of population abundance of sockeye salmon (Oncorhynchus nerka). We show that between‐year variability in population productivity (process variation) and, to a lesser extent, variability in abundance estimates (observation error) are important causes of unreliable identification of population status. We found that using all available data, rather than just the most recent three generations, consistently improved the reliability of risk assessments. The approach outlined here can improve understanding of the reliability of risk assessments, thereby reducing concerns that may impede their use for exploited taxa such as marine fishes.

Challenges for the Kasatoshi volcano hypothesis as the cause of a large return of sockeye salmon (Oncorhynchus nerka) to the Fraser River in 2010

AbstractIn August 2008 the Kasatoshi volcano in the Aleutian archipelago erupted. Prevailing winds carried volcanic ash to the Gulf of Alaska, where its soluble iron dissolved and initiated a widespread phytoplankton bloom. Two years later, the abundance of sockeye salmon (Oncorhynchus nerka) returning to spawn in the Fraser River was larger than any observed since 1913. Kasatoshi's influence on growth and survival has been proposed as the ultimate cause of the abundant return. However, when relevant data are brought to bear on the hypothesis, it shows that: (1) survival of the abundant sockeye salmon cohort was unremarkable when compared with the historical record; (2) without an accompanying volcano, survival of the returns in 2011 was about the same as in 2010; (3) parental abundance that spawned the abundant return in 2010 was the sixth largest since 1948; (4) during their first summer at sea, sockeye salmon are not known to migrate in the offshore region where the anomalous chlorophyll bloom occurred; (5) an older cohort that was likely exposed to the chlorophyll bloom had the second lowest productivity on record when it returned in 2009; (6) immature sockeye salmon do not feed on diatoms, so any trophodynamic benefit derived from excess chlorophyll in mid‐to late August 2008 would have to have found a rapid trophic pathway to sockeye salmon on the continental shelf; and (7) no other populations of sockeye salmon or other species of salmon that are known to rear in the same region had unexpectedly high returns.

Conservation Biology through the Lens of a Career in Salmon Conservation

Conservation Biology through the Lens of a Career in Salmon Conservation

Physiological impairment of adult sockeye salmon in fresh water after simulated capture-and-release across a range of temperatures

Sockeye salmon abundance in the Fraser River has declined precipitously over the past two decades, reducing fishing opportunities for this ecologically, culturally and economically valuable species. Release of non-target species that are captured incidentally is a growing conservation measure used in managing mixed species fisheries. Fraser River sockeye salmon are released from commercial, First Nations, and recreational fisheries, however little research exists investigating the fitness and fate of released sockeye salmon, and none examine how the effect of ecologically relevant temperature ranges interact with capture stressors. We exposed adult migrating summer-run sockeye in freshwater to simulated capture and release stressors, including exhaustive exercise and air exposure, at temperatures spanning the range of historic, current and predicted future migration conditions in the Fraser River (13 °C, 19 °C, and 21 °C) to understand the physiological consequences of these stressors acting in synergy. Three minutes of exhaustive exercise significantly raised the plasma lactate, chloride, sodium, and osmolality, and lowered the plasma potassium of these fish, and one minute of air exposure following exercise elevated glucose (females only) and exacerbated high lactate levels. The inability of all air-exposed fish in the warmest temperatures to maintain equilibrium upon return to the water is evidence of the effects of warm temperatures. Fewer than half of the air-exposed fish in the coolest temperature demonstrated this impairment. Further, air exposure resulted in a marked depression of ventilation rates in the warmest temperatures. This is the first experiment investigating the physiological disturbance of capture and release at various temperatures on adult Pacific salmon, and the results suggest a need for better understanding of the potential fitness consequences to improve the management of this important resource.

Implications of a warming eastern Bering Sea for Bristol Bay sockeye salmon

AbstractFarley, E. V., Starovoytov, A., Naydenko, S., Heintz, R., Trudel, M., Guthrie, C., Eisner, L., Guyon, J. R. 2011. Implications of a warming eastern Bering Sea for Bristol Bay sockeye salmon. – ICES Journal of Marine Science, 68: 1138–1146. Overwinter survival of Pacific salmon (Oncorhynchus sp.) is believed to be a function of size and energetic status they gain during their first summer at sea. We test this notion for Bristol Bay sockeye salmon (O. nerka), utilizing data from large-scale fisheries and oceanographic surveys conducted during mid-August to September 2002–2008 and from February to March 2009. The new data presented in this paper demonstrate size-selective mortality for Bristol Bay sockeye salmon between autumn and their first winter at sea. Differences in the seasonal energetic signatures for lipid and protein suggest that these fish are not starving, but instead the larger fish caught during winter apparently are utilizing energy stores to minimize predation. Energetic status of juvenile sockeye salmon was also strongly related to marine survival indices and years with lower energetic status apparently are a function of density-dependent processes associated with high abundance of juvenile sockeye salmon. Based on new information regarding eastern Bering Sea ecosystem productivity under a climate-warming scenario, we hypothesize that sustained increases in spring and summer sea temperatures may negatively affect energetic status of juvenile sockeye salmon, potentially resulting in increased overwinter mortality.

Pacific salmon abundance trends and climate change

Abstract Irvine, J. R., and Fukuwaka, M. 2011. Pacific salmon abundance trends and climate change. – ICES Journal of Marine Science, 68: 1122–1130. Understanding reasons for historical patterns in salmon abundance could help anticipate future climate-related changes. Recent salmon abundance in the northern North Pacific Ocean, as indexed by commercial catches, has been among the highest on record, with no indication of decline; the 2009 catch was the highest to date. Although the North Pacific Ocean continues to produce large quantities of Pacific salmon, temporal abundance patterns vary among species and areas. Currently, pink and chum salmon are very abundant overall and Chinook and coho salmon are less abundant than they were previously, whereas sockeye salmon abundance varies among areas. Analyses confirm climate-related shifts in abundance, associated with reported ecosystem regime shifts in approximately 1947, 1977, and 1989. We found little evidence to support a major shift after 1989. From 1990, generally favourable climate-related marine conditions in the western North Pacific Ocean, as well as expanding hatchery operations and improving hatchery technologies, are increasing abundances of chum and pink salmon. In the eastern North Pacific Ocean, climate-related changes are apparently playing a role in increasing chum and pink salmon abundances and declining numbers of coho and Chinook salmon.

Indigenous culture and adaptation to climate change: sockeye salmon and the St’át’imc people

This paper provides a culturally-informed understanding of the impacts of climate change on a highly important subsistence activity that has been practiced by First Nations of central British Columbia for thousands of years. The paper begins with a review of the science regarding sockeye salmon and climate change. It discusses harvest patterns, and how the timing of runs has changed. A survey was conducted by the first author regarding St’at’imc traditional fishing at a historic site on the Fraser River, in 2005. The results show that the impacts of climate change are apparent to those conducting traditional fishing practices, in terms of changed timing and abundance of salmon runs. These perceptions fit closely with the information available from scientists and management agencies. These changes are highly problematic for the St’at’imc, in that the preservation method (drying) is tied to seasonal weather patterns. The whole cultural setting, and the relevance of salmon for subsistence would be highly altered by climate change that leads to changes in the timing and abundance of sockeye salmon. The paper discusses mitigation and adaptation alternatives, but also indicates the scope of these seem limited, given the resource systems and the context of these activities.

Density-dependent growth of Alaska sockeye salmon in relation to climate–oceanic regimes, population abundance, and body size, 1925 to 1998

To better understand how density- dependent growth of ocean-dwelling Pacific salmon varied with climate and population dynamics, we examined the marine growth of sockeye salmon Oncorhynchus nerka in relation to an index of sockeye salmon abundances among climate regimes, popu- lation abundances, and body sizes under varied life- history stages, from 1925 to 1998, using ordinary least squares and multivariate adaptive regression spline threshold models. The annual marine growth and body size during the juvenile, immature, and maturing life stages were estimated from growth pattern incre- ments on the scales of adult age 2.2 sockeye salmon that returned to spawn at Karluk River and Lake on Kodiak Island, Alaska. Intra-specific density-depen- dent growth was inferred from inverse relationships between growth and sockeye salmon abundance based on commercial harvest. Density-dependent growth occurred in all marine life stages, during the cool regime, at lower abundance levels, and at smaller body sizes at the start of the juvenile life stage. The finding that density dependence occurred during the cool regime and at low population abundances sug- gests that a shift to a cool regime or extreme warm regime at higher population abundances could further reduce the marine growth of salmon and increase competition for resources.

Linkages between Alaskan sockeye salmon abundance, growth at sea, and climate, 1955–2002

We tested the hypothesis that increased growth of salmon during early marine life contributed to greater survival and abundance of salmon following the 1976/1977 climate regime shift and that this, in turn, led to density-dependent reductions in growth during late marine stages. Annual measurements of Bristol Bay (Bering Sea) and Chignik (Gulf of Alaska) sockeye salmon scale growth from 1955 to 2002 were used as indices of body growth. During the first and second years at sea, growth of both stocks tended to be higher after the 1976–1977 climate shift, whereas growth during the third year and homeward migration was often below average. Multiple regression models indicated that return per spawner of Bristol Bay sockeye salmon and adult abundance of western and central Alaska sockeye salmon were positively correlated with growth during the first 2 years at sea and negatively correlated with growth during later life stages. After accounting for competition between Bristol Bay sockeye and Asian pink salmon, age-specific adult length of Bristol Bay salmon increased after the 1976–1977 regime shift, then decreased after the 1989 climate shift. Late marine growth and age-specific adult length of Bristol Bay salmon was exceptionally low after 1989, possibly reducing their reproductive potential. These findings support the hypothesis that greater marine growth during the first 2 years at sea contributed to greater salmon survival and abundance, which in turn led to density-dependent growth during later life stages when size-related mortality was likely lower. Our findings provide new evidence supporting the importance of bottom-up control in marine ecosystems and highlight the complex dynamics of species interactions that continually change as salmon grow and mature in the ocean. r 2007 Elsevier Ltd. All rights reserved.

Caveats on the use of paleolimnology to infer Pacific salmon returns

The ability of paleolimnology to reconstruct historical sockeye salmon (Oncorhynchus nerka) abundance was assessed at Fraser Lake, an important nursery lake in the interior of British Columbia (BC), Canada. Multiple sediment proxies of lake production, as well as nitrogen and carbon stable isotopes, all portray relatively complacent stratigraphies, despite well‐monitored changes in salmon returns over the most recent 60 years. The separation of autochthonous from total sediment organic matter did not clarify the identification of the nitrogen isotopic fingerprint of marine‐derived nutrients (MDN). Slight shifts in diatom assemblages are better interpreted as responses to either early human activities in the catchment or post‐Little Ice Age climate warming. The low proportion of MDN in the lake's annual budget (3% N and 7% P) is the probable reason their influence is not expressed in lake sediments. Thus, paleolimnology is incapable of providing unequivocal inferences concerning historical salmon abundances in Fraser Lake, in contrast to lakes from southern Alaska, where the same techniques have yielded unambiguous results. Sediment MDN proxies, together with catchment characteristics and escapement data, were collated for an additional nine sockeye nursery lakes spanning southern Alaska to southern BC. Primary production and biogeochemical cycling in Alaskan nursery lakes appears largely driven by MDN from sockeye returns, whereas BC lakes are more strongly influenced by allochthonous organic matter and lake‐water residence times. Alaskan lakes possess the limnological features that are prerequisite for meaningful salmon reconstructions using paleolimnology, while lakes from southern BC do not. This does not suggest that MDN are unimportant in southern BC lakes but rather that they are not readily disentangled from other factors that shape the paleolimnological record.