Pink Salmon Abundance Research Articles

Cycles in adult steelhead length suggest interspecific competition in the North Pacific Ocean

Anadromous fishes rely on abundant prey in the ocean to grow large quickly, but prey limitation leads to interspecific competition. When species interactions are difficult to observe, growth can be studied to detect otherwise cryptic signals of competition. We describe a previously undocumented 2-year cycle in the lengths of adult natural-origin steelhead ( Oncorhynchus mykiss) returning to spawn in the Snake River Basin. Returning steelhead were 38 mm shorter on odd return years, not accounting for sex, stock, and years of ocean residence. The well-known cycle in abundance of pink salmon ( Oncorhynchus gorbuscha) from eastern Kamchatka and North America had statistically significant negative effects on returning steelhead lengths that depended on sex and the number of years of ocean residence. These results suggest that competition for limited resources occurs well after initial ocean entry and that interactions during later stages of ocean residence can be influential. Interspecific competition has implications for future returns of steelhead from the ocean, especially as metabolic demands for steelhead increase as the ocean warms.

Description of regression models for predicting the dynamics of pink salmon returns in the Kamchatka region based on climate-oceanological and population-genetic data

Several regression models for predicting returns of pink salmon in the Kamchatka region are presented. The data for 1990–2023 were analyzed. Among available climatic and oceanological indices, the most suitable for using as predictors for forecasting of pink salmon returns were the Pacific Decadal Oscillation (PDO) index, Western Pacific Cyclonic Index (WP), Arctic Oscillation (AO) index, and the sea surface temperature anomaly in the North Pacific. Multi-dimensional models of the «stock–recruitment» type were built on identified statistical patterns, which allowed to estimate potential abundance of the pink salmon returns to northeastern and western Kamchatka. Besides, methods for predicting the abundance of pink salmon returns on the data of fish counting in the sea are considered, using the materials of TINRO trawl surveys conducted in the Bering and Okhotsk Seas in the fall seasons of 2012–2023. To determine the abundance of pink salmon originated from West Kamchatka, genetic identification of regional composition of juveniles in mixed trawl catches was used. All tested methods have a high level of determination, but simpler regressive models are more prospective for practical forecasting of general trend in dynamics of pink salmon stocks in the Kamchatka region due to very weak generalization ability of more complicated models.

Ecological implications of the pink salmon invasion in northern Norway-Aggregative responses and terrestrial transfer by white-tailed eagles.

Over the last 10 years, the spawning population of invasive pink salmon (Oncorhynchus gorbuscha) has increased in the river systems in northern Norway to a level that is causing concern about their impact on endemic fauna and ecosystem processes. The scale of transfer of pink salmon carcasses into the terrestrial ecosystem is likely to be a key determinant of terrestrial impact. Bears (Ursus sp.) are responsible for most such transfers in North America but are rare in Norway. The white-tailed eagle (Haliaeetus albicilla) is common however, and a candidate to be a main cause of such transfers. To evaluate this hypothesis, data on the abundance of white-tailed eagles and pink salmon were collected along the river Skallelv in northern Norway in 2021, a year the pink salmon spawned in the river, and in 2022, a year no pink salmon spawned in the river. The abundance of white-tailed eagles along the river was much higher the year pink salmon spawned in the river. Furthermore, white-tailed eagles were observed aggregating and catching pink salmon where and when pink salmon were present at the spawning and post-spawning stages. Based on our observations, we suggest that the white-tailed eagle is the main species involved in the transport of pink salmon from the river into the riparian zone in northern Norway and that other scavengers, in particular the red fox (Vulpes vulpes) and common raven (Corvus corax), play an important role in transporting pink salmon carcasses from the riparian zone to the wider terrestrial ecosystem.

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.

Factors Determining the Replenishment of Pink Salmon Oncorhynchus gorbuscha (Salmonidae) on Iturup Island

Based on the data on the abundance of 53 generations of pink salmon Oncorhynchus gorbuscha of Iturup Island (spawners on spawning grounds, downstream migrating juveniles and the return of mature fish), a model describing the dependence of the abundance of mature pink salmon offspring on the initial abundance of generations and the effect of external factors was constructed using nonlinear regression analysis. The model explains about 80% of the replenishment variability, and it depends more on the effect of external factors in the freshwater period of life. The variability of replenishment is most closely related to factors related to the hydrological regime of rivers. The dependence of replenishment on the abundance of juveniles migrating downstream from spawning grounds, described by the dome-shaped curve, indicates the limiting effect of density factors on the formation of the abundance of pink salmon during the marine period of life. At the same time, a statistically significant effect of the abundance of juveniles released from fish hatcheries on the dynamics of the replenishment was not found.

Geographic distribution, abundance, diet, and body size of invasive pink salmon (Oncorhynchus gorbuscha) in the Norwegian and Barents Seas, and in Norwegian rivers

AbstractWe report for the first time the geographic distribution, abundance, diet, and body size of invasive pink salmon (Oncorhynchus gorbuscha) in the Norwegian and Barents Seas and Norwegian coast and rivers. We found that pink salmon have spread throughout the Norwegian Sea and along the Norwegian coast, and abundance increased by several orders of magnitude in 2017, with no signs that it has peaked. Marine pink salmon diet comprised mainly fish larvae, amphipods, and krill, but their relative importance varied with geographic distribution. North of 67.5°N, Amphipoda, herring, and saithe were more important, while south of 67.5°N, Euphausiidae and mesopelagic fish abounded. Pink salmon body size was larger in the northern rivers, and to the north of the Norwegian Sea and the Barents Sea, relative to the southern rivers and sea areas. Pink salmon were feeding in the ocean during the winter and spring, and in coastal areas immediately before return to the rivers, but not after they had entered the rivers. There was no geographical pattern in the seasonal timing of river ascent. The geographic pattern in abundance and diet of pink salmon, as reported here, offer a measure of the ecological effect of the invasion.

The Dynamics of the Abundance and Intrapopulation Structure of Pink Salmon at the Western and Northeastern Coasts of Kamchatka

The Dynamics of the Abundance and Intrapopulation Structure of Pink Salmon at the Western and Northeastern Coasts of Kamchatka

Bayesian Nonparametric Density Autoregression with Lag Selection

We develop a Bayesian nonparametric autoregressive model applied to flexibly estimate general transition densities exhibiting nonlinear lag dependence. Our approach is related to Bayesian density regression using Dirichlet process mixtures, with the Markovian likelihood defined through the conditional distribution obtained from the mixture. This results in a Bayesian nonparametric extension of a mixtures-of-experts model formulation. We address computational challenges to posterior sampling that arise from the Markovian structure in the likelihood. The base model is illustrated with synthetic data from a classical model for population dynamics, as well as a series of waiting times between eruptions of Old Faithful Geyser. We study inferences available through the base model before extending the methodology to include automatic relevance detection among a pre-specified set of lags. Inference for global and local lag selection is explored with additional simulation studies, and the methods are illustrated through analysis of an annual time series of pink salmon abundance in a stream in Alaska. We further explore and compare transition density estimation performance for alternative configurations of the proposed model. Supplementary materials are available online.

Composition of nekton and jellyfishes communities and the results of trawl survey for estimation of abundance of pre-anadromous migrations pink salmon (<i>Oncorhynchus gorbuscha</i>) in the north-western Pacific Ocean in summer 2021

As a result, of a trawl survey performed in the Pacific waters of the Kuril Islands within the EEZ of the Russian Federation and outside the external border of the EEZ of the Russian Federation, the abundance and biomass of all representatives of nekton and macroplankton were determined. Peculiarities of the spatial distribution of massive representatives of pelagic nekton and jellyfish were revealed. According to the summer survey of the upper epipelagic layer of the Pacific waters, the abundance and biomass of Pacific salmon during their pre-anadromous migrations to the rivers of the Okhotsk Sea basin were taken into account and the main concentrations of mature pink salmon were outlined. During the survey, data on the biological state of salmon in mixed clusters were obtained and preliminary spatial differentiation of the early and late pink salmon stock belonging to different regions of the Okhotsk Sea was performed.

Dynamics of abundance and intrapopulation structure of pink salmon at the western and northeastern coasts of Kamchatka

Interannual changes of the pink salmon abundance at the western and northeastern coasts of Kamchatka are analyzed. Local stocks with certain patterns of the abundance dynamics are revealed. Contribution of these local groups to the overall reproduction of the regional macro-complexes and catch of pink salmon in the 1957–2020 is considered. Prospects of the reproduction and catch are evaluated. Taking into account the revealed heterogeneity of the population dynamics in spatially isolated groups within macro-complexes, quality of forecasting the pink salmon stocks and catches at Kamchatka could be improved.

Did Recent Marine Heatwaves and Record High Pink Salmon Abundance Lead to a Tipping Point that Caused Record Declines in North Pacific Salmon Abundance and Harvest in 2020?

Did Recent Marine Heatwaves and Record High Pink Salmon Abundance Lead to a Tipping Point that Caused Record Declines in North Pacific Salmon Abundance and Harvest in 2020?

Estimation and Selection for High-Order Markov Chains with Bayesian Mixture Transition Distribution Models

We develop a mixture model and diagnostic for Bayesian estimation and selection in high-order, discrete-state Markov chains. Both extend the mixture transition distribution, which constructs a transition probability tensor by aggregating probabilities from a set of single-lag transition matrices, through inclusion of mixture components dependent on multiple lags. We demonstrate two uses for the proposed model: identification of relevant lags through over-specification and shrinkage via priors for sparse probability vectors, and parsimonious approximation of multi-lag dynamics by mixing low-order transition models. The diagnostic yields a general and interpretable mixture decomposition for transition probability tensors estimated by any means. We demonstrate the utility of the model and diagnostic with simulation studies, and further apply the methodology to a data analysis from the high-order Markov chain literature, and to a time series of pink salmon abundance in Alaska, United States. Supplemental files for this article are available online.

Puget Sound Chum Salmon Growth Linked to Competitor Abundance, Climate Indices, and Copepod Species Richness

AbstractAn improved understanding of the mechanisms influencing productivity of fish populations is critical for accurately determining harvest rates and identifying years of conservation concern. Here we reconstruct yearly scale growth of three Puget Sound (PS) Chum Salmon Oncorhynchus keta stocks over 16 brood years (1997–2012) to better understand how variation in marine growth may be related to environmental factors, intra‐ and interspecific competition, and stock productivity. Generalized additive mixed models identified copepod species richness in the northern California Current and the abundance of PS Pink Salmon O. gorbuscha and Chum Salmon as strong predictors of first‐year growth, the latter indicative of density‐dependent effects as the abundance of local competitors (Pink and Chum salmon) increased. Second‐year growth was negatively related to the Aleutian Low–Beaufort Sea Anticyclone (ALBSA), a recently defined metric of the Aleutian Low, and showed a nonlinear positive to negative relationship with sea surface temperature in the Gulf of Alaska. Puget Sound Chum and Pink Salmon abundances were also significantly related to second‐year growth but did not suggest density‐dependent effects like those observed in ocean year 1. Third‐year growth was closely related to large‐scale climate indicators, demonstrating a nonlinear negative to positive relationship with the North Pacific Gyre Oscillation, a negative relationship with ALBSA, and a negative relationship with North Pacific Pink Salmon abundance when catch statistics indicated that abundance was high. Models indicated that PS Chum Salmon stock productivity (recruits per spawner) was positively correlated with back‐calculated first‐year growth and negatively correlated with second‐ and third‐year growth, suggesting that for brood years whose surviving adults experienced rapid early marine growth, there were cohort survival benefits. As new relationships between large‐scale indicators and Pacific salmon stocks are identified, incorporating these indicators into forecasting efforts is paramount for effective and sustainable management of fishery resources.

Growth features for pink salmon <i>Oncorhynchus gorbuscha</i> in generations with different survival rate in the marine period of life

There is believed in classical fishery ichthyology, that slower growth can be a reason for decreasing of fish abundance. A sharp decrease occurred recently in the pink salmon abundance on the eastern coast of Sakhalin Island that inspired this study of growth in the pink generations with different survival during the marine period of life. The growth rates were determined using the scale measurements for the pink salmon returned to the southeastern coast of Sakhalin in 2005-2018. The growth parameters (length increments, variability and asymmetry of size composition) were compared with the survival rate of corresponding year-classes. Slower growth coincided with lower survival for feeding fry only, i.e. in the early marine period of pink salmon life. So, the hypothesis is not confirmed about a «crucial size» for salmon juveniles that must be reached until the end of summer-autumn feeding to survive during wintering. That means that previous estimations of size-selective mortality of pink juveniles are not realistic because of both inadequate samplings and reconstructions in size composition during the juveniles growth.

Competition with odd-year pink salmon in the ocean affects natural populations of chum salmon from Washington

Over the last 5 decades, natural populations of pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon were the most abundant salmon species returning to Washington, USA. Pink salmon predominantly returned in odd years, and chum salmon stocks that interacted with pink salmon exhibited strong even- and odd-year variations in abundance, size, age-at-maturity, and productivity (recruits-per-spawner). We investigated the effects of competition between pink and chum salmon originating from Washington during different life-history phases. Overall, chum salmon returns were 34% lower in pink salmon (odd) years compared to non-pink salmon (even) years. Chum salmon productivity tended to be below average for odd broods, especially along the Washington coast where there are no pink salmon populations, suggesting that competition during overlapping marine periods established their distinct even- and odd-year patterns. We evaluated long-term trends in chum (and pink) salmon productivity using correlation and time series analysis and examined the influence of ocean indicators on those trends. In general, chum salmon productivity increased between brood years 1968 and 1989 and was positively related to summertime Pacific Decadal Oscillation (PDO), but declined between brood years 1990 and 2012 and was negatively related to the PDO. Pink salmon productivity had no directional trend, but exhibited declines over the last decade and was negatively related to the PDO over the entire time series. Chum salmon productivity was also negatively related to pink salmon abundance, supporting the conclusion that ocean conditions and competition accounted for brood-year differences in chum salmon age-at-maturity and lower returns in odd versus even years.

Comparative characteristics of growth of the scales from pink salmon in returns to Sakhalin Island (southeast coast) and Iturup Island in 2017 and 2018

Iturup Island (in southern Kuril Islands) and southeastern Sakhalin Island are known by the highest catches of salmons within the Sakhalin-Kuril region. The timing of pink salmon mass return to Iturup is 5–10 days later than to Sakhalin, and the females returned to Iturup have higher relative individual fecundity, on average. In 2014, an unexpected increase of pink salmon catches occurred on southeastern Sakhalin Island, with a simultaneous sharp decrease of the catches on Iturup Island. Assumption on appearance of Kuril pink salmon in the Sakhalin waters was confirmed by analysis of the scale parameters (number of sclerites and intercirculi distance in the first-year scale zone), dynamics of catches, and individual fecundity of females. Sharp opposite changes of the pink salmon catch dynamics were noted again for these areas in 2017 and 2018. Such changes of pink salmon abundance could be reasoned by environmental conditions of reproduction in these areas or new redistribution between two areas. To clarify the issue, complex analysis (same as for 2014) was applied for pink salmon at southeastern Sakhalin and Iturup in 2017 and 2018 (187 and 215 fish samples from Sakhalin and 194 and 152 fish samples from Iturup in these two years, respectively). The results were interpreted following the hypothesis of fluctuating stocks. Taking into account the complex of traits, there is concluded that the assumption about redistribution of pink salmon between southeastern Sakhalin and Iturup Island in 2017 and 2018 is untenable.

Correspondence between scale growth, feeding conditions, and survival of adult Chinook salmon returning to Puget Sound and coastal Washington: Implications for forecasting

In this study, we used scale analysis of returning adults to examine the relationship between early marine growth and survival for Chinook salmon (Oncorhynchus tshawytscha) returning to the Puget Sound and coastal Washington, USA. In total, we examined scales from 2604 individuals from 5 stocks over 7 outmigration years characterized by a range of survival conditions (range from 0.11 to 9.50%). We observed a positive relationship between growth during the first year at sea and survival for adults returning to Puget Sound and the Washington coast. Scale growth during the first year at sea did not co-vary between coastal Washington and Puget Sound stocks, and in most years coastal Chinook salmon attained a larger size at the end of the first year at sea. Large scale oceanographic variables (PDO, NPGO) were not significantly related to variation in scale growth, but for some Puget Sound populations, scale growth was higher in years of cooler sea surface temperatures and lower Pink salmon (O. gorbuscha) abundance. We developed a biological indicator for forecasting cohort survival of Tumwater Falls hatchery Chinook salmon on the Deschutes River, WA using marine growth estimates of the earliest returning fish (age-21). The marine growth index predicted survival better for 8 brood years compared to a recent 5 year average returns forecasting approach (3.40% vs 35.41% Mean Percent Error). Results from this study suggest that early marine growth is important to the survival of Puget Sound and coastal Washington Chinook salmon and may be a useful biological indicator to improve pre-season forecasting of Chinook salmon populations in Washington State.

Density‐dependent effects of eastern Kamchatka pink salmon (Oncorhynchus gorbuscha) and Japanese chum salmon (O. keta) on age‐specific growth of western Alaska chum salmon

AbstractHatcheries release >4.5 billion juvenile Pacific salmon (Oncorhynchus spp.) into the North Pacific Ocean annually, raising concerns about competition with wild salmon populations. We used retrospective scale analysis to investigate how the growth of chum salmon (O. keta) from western Alaska is affected by the abundance of chum salmon from Japanese hatcheries and wild pink salmon (O. gorbuscha) from the Russian Far East. Over nearly five decades, the growth of Kuskokwim River chum salmon was negatively correlated with the abundance of Japanese hatchery chum salmon after accounting for the effects of sex and spring/summer sea‐surface temperature in the Bering Sea. An effect of wild eastern Kamchatka pink salmon abundance on the growth of Kuskokwim River salmon was detectable but modest compared to the intraspecific competitive effect. A decrease in Japanese hatchery chum salmon releases in 2011–2013 was not associated with increased growth of Bering Sea chum salmon. However, the abundance of wild chum salmon from the Russian Far East increased during that time, possibly obscuring reduced competition with hatchery chum salmon. Our results support previous evidence that chum salmon are affected by intraspecific competition, and to a lesser extent interspecific competition, in the North Pacific, underscoring that the effects of salmon hatchery production transcend national boundaries.

Competition-driven growth of Atka mackerel in the Aleutian Islands ecosystem revealed by an otolith biochronology

Fish otolith increment biochronologies can reveal factors contributing to growth. These annually resolved, multi-decadal biochronologies have been used to identify temporal and spatial patterns in growth variability. Here, we used a linear mixed modeling approach to determine the relative importance of intrinsic factors (e.g., sex, age) and extrinsic factors (e.g., temperature, abundance of con-specifics and competitors) to growth of Atka mackerel (Pleurogrammus monopterygius), a commercially important groundfish dominant in the Aleutian Islands ecosystem. A yearly alternating pattern of wide and narrow increments was observed, and was negatively correlated with abundance of pink salmon (Oncorhynchus gorbuscha), suggesting possible competition over shared food resources such as large copepods (which were positively correlated with the otolith biochronology). There was no detectable effect of temperature on otolith growth, which could be a result of relative stability in water temperatures at the study site. We also contrast the otolith biochronology with a body condition index to examine the relationship between otolith and somatic growth. This represents the first otolith biochronology developed in the Aleutian Islands and provides insight into potential species interactions and their impacts on growth within this highly dynamic and productive ecosystem.