Abundance Of Chinook Salmon Research Articles

Back from the brink: Estimating daily and annual abundance of natural-origin salmon smolts from 30-years of mixed-origin capture-recapture data

Evaluating the status and trends of natural-origin anadromous fish populations over time requires robust estimates of out-migrating juvenile abundance. Information on abundance is typically acquired by capturing actively migrating fish as they pass stationary monitoring platforms. Challenges to estimation include protracted migration timing, temporally varying capture probabilities and the contemporaneous presence of unmarked hatchery-origin fish. The confounding effects of unmarked hatchery fish are especially pernicious in systems hosting multiple hatchery programs with variable mark-rates among releases. Here, we address this problem for a regionally and culturally important population of Chinook salmon (Oncorhynchus tshawytscha) supported by a hatchery-supplementation program implemented in response to the listing of this population under the U.S. Endangered Species Act. We developed a model to estimate daily and annual abundance of naturally produced age-0 fall Chinook salmon passing Lower Granite Dam (Snake River, USA) for each of the last 30 years. We accounted for variable hatchery marking rates by integrating two related data sources: 1) release-recapture data of fish with individually identifiable tags and 2) counts of marked and unmarked sample of fish captured each day. We fit joint parameters for daily fish arrival and capture probabilities to these data to estimate the daily abundance of hatchery- and natural-origin fish. Our results show that from 1992 to 2021, the annual abundance of juvenile natural-origin Snake River fall Chinook salmon increased by two orders of magnitude. These results are the first comprehensive evaluation of multi-decadal trends in abundance and run-timing for this population. Our approach can be adapted to other runs and locations within the Columbia River basin or similar systems where out-migrating fish are monitored at fixed locations.

Visual and genetic stock identification of a test fishery to forecast Columbia River spring Chinook salmon stocks 2 weeks into the future.

Modern fisheries management strives to balance opposing goals of protection for weak stocks and opportunity for harvesting healthy stocks. Test fisheries can aid management of anadromous fishes if they can forecast the strength and timing of an annual run with adequate time to allow fisheries planning. Integration of genetic stock identification (GSI) can further maximize utility of test fisheries by resolving run forecasts into weak- and healthy-stock subcomponents. Using 5 years (2017-2022) of test fishery data, our study evaluated accuracy, resolution, and lead time of predictions for stock-specific run timing and abundance of Columbia River spring Chinook salmon (Oncorhynchus tshawytscha). We determined if this test fishery (1) could use visual stock identification (VSI) to forecast at the coarse stock resolution (i.e., classification of "lower" vs. "upriver" stocks) upon which current management is based and (2) could be enhanced with GSI to forecast at higher stock resolution. VSI accurately identified coarse stocks (83.3% GSI concordance), and estimated a proxy for abundance (catch per unit effort, CPUE) of the upriver stock in the test fishery that was correlated (R 2 = 0.90) with spring Chinook salmon abundance at Bonneville dam (Rkm 235). Salmon travel rates (~8.6 Rkm/day) provided predictions with 2-week lead time prior to dam passage. Importantly, GSI resolved this predictive ability as finely as the hatchery broodstock level. Lower river stock CPUE in the test fishery was correlated with abundance at Willamette Falls (Rkm 196, R 2 = 0.62), but could not be as finely resolved as achieved for upriver stocks. We described steps to combine VSI and GSI to provide timely in-season information and with prediction accuracy of ~12.4 mean absolute percentage error and high stock resolution to help plan Columbia River mainstem fisheries.

Identifying drivers of demographic rates in an at‐risk population of marine mammals using integrated population models

AbstractEffective conservation of threatened populations requires identification of the processes limiting recovery. When multiple population processes are potentially limiting, they are sometimes analyzed independently, often using different datasets. Analytically, this is suboptimal, as processes are often correlated, which can lead to biased estimates of parameters and quantities of interest. Integrated population models (IPMs) can synthesize several data streams in the same probabilistic framework to circumvent these issues. Lack of prey was identified as one of the primary threats to recovery of critically endangered southern resident killer whales (SRKWs), Orcinus orca. Previous studies have correlated SRKW demographic rates with indices of Chinook salmon Oncorhynchus tshawytscha abundance, but these approaches have modeled reproduction and survival independently. We developed an IPM for SRKWs that models both processes simultaneously, as a function of Chinook salmon abundance along the west coast of North America. We used this model to evaluate the relationship between Chinook salmon abundance and demographic rates of SRKWs, with the goal of updating our understanding of a potential causal relationship between prey availability and SRKW population dynamics, and how these relationships may have changed over time. Results suggest that SRKW mortality rates are more strongly associated with Chinook salmon abundance than birth rates. Our analysis also suggests northern resident killer whale abundance could also be affecting SRKW carrying capacity, possibly through competition over shared prey resources. The IPM fit observed total abundance data well and predicted temporal changes in population demographics with reasonable accuracy, but small sample size may have opacified model selection. Our approach offers a valuable tool for predicting the response of the SRKW population to alternative management strategies involving the recovery of Chinook salmon stocks in the eastern Pacific.

Status of a stocked Atlantic salmon population in Lake Huron

In 2011, the Michigan Department of Natural Resources (MDNR) expanded stocking of Atlantic salmon (Salmo salar) in Lake Huron to enhance fishing opportunities following Chinook salmon (Oncorhynchus tshawytscha) abundance declines. Currently, little is known about the population produced from this stocking. We fit an assessment model to harvest data from Michigan jurisdictional waters to estimate Atlantic salmon population dynamics and abundance. Because of potential biases in MDNR creel survey harvest estimates, a survey was e-mailed to online purchasers of a 2019 Michigan fishing license asking about where and when Atlantic salmon were harvested to correct creel harvest estimates. Anglers were also asked about catch-and-release angling and tested on their ability to identify Lake Huron salmonids. Creel harvest estimates overlapped spatially and temporally with 42% of survey reported Atlantic salmon harvest. After correcting creel harvest estimates, total abundance of Atlantic salmon in 2019 was estimated at approximately 392,000 fish with a peak abundance of approximately 406,000 fish. Anglers released 27% of caught fish and correctly identified Atlantic salmon 28% of the time. To assess the occurrence of food resource competition, differences in condition (i.e., expected weight at length) were evaluated. Condition was higher in later years than in earlier years despite abundance increases. Our results suggested that past stocking established a population of approximately 400,000 Atlantic salmon with evidence suggesting that fish were finding sufficient food resources. Future Atlantic salmon management efforts may be improved by quantifying post-stocking survival rates and other sources (e.g., charter, Canadian) of harvest.

Methods for assessing and responding to bias and uncertainty in U.S. West Coast salmon abundance forecasts

We quantified the bias and accuracy of U.S. West Coast Chinook and coho salmon abundance forecasts using lognormal distributions fitted to annual ratios between postseason abundance estimates and preseason forecasts, or constrained to assume unbiased forecasts. Accuracy was modest to low, with CVs exceeding 50% for 8/19 Chinook and 17/17 coho stocks. We evaluated the fitted median as a bias correction, and uncertainty buffers based on quantiles below the median. We tested whether retrospective application of bias corrections and/or buffers brought forecasts closer on average to postseason estimates; and performed retrospective and prospective analyses of consequences for stock status, harvest, and escapement for Sacramento River Fall Chinook (SRFC), a key fishery stock. Bias corrections and/or buffers improved most forecasts, with buffers providing improvement more often. For SRFC, bias correction alone could have led to one less year of overfished status, while buffers could have further shortened or avoided overfished status and reduced the frequency of under-escapement. Reductions in mean annual harvest resulting from applying bias corrections and/or moderate buffers were predicted to be smaller than the increases in harvest resulting from forecast and implementation error. Prospective simulations showed buffers could reduce risks of overfished status and under-escapement, at small costs to long-term mean harvests. However, this metric misses substantial harvest reductions in some years, since mean harvest is most sensitive to harvest at high abundance; though our analyses also neglected benefits of increased escapement for future production. Future work should incorporate observation error and nonstationarity, and the combined effects of forecast and implementation error on the probability of missing escapement goals.

Requirements and availability of prey for northeastern pacific southern resident killer whales.

The salmon-eating Southern Resident killer whale (SRKW) (Orcinus orca) population currently comprises only 73 individuals, and is listed as ‘endangered’ under the Species at Risk Act in Canada. Recent evidence suggests that the growth of this population may be limited by food resources, especially Chinook salmon (Oncorhynchus tshawytscha). We present spatio-temporal bioenergetics model for SRKW in the Salish Sea and the West Coast of Vancouver Island from 1979–2020 with the objective of evaluating how changes in the abundance, age-structure, and length-at-age of Chinook salmon populations has influenced the daily food consumption of the SRKW population. Our model showed that the SRKW population has been in energetic deficit for six of the last 40 years. Our results also suggested that the abundance of age-4 and age-5 Chinook salmon are significant predictors of energy intake for SRKW. We estimated that the annual consumption (April-October) of Chinook salmon by the whales between 1979 and 2020 ranged from 166,000 216,300. Over the past 40 years, the model estimated that the contribution in the predicted SRKW diet of Chinook salmon originating from the Columbia River has increased by about 34%, and decreased by about 15% for Chinook salmon stocks originating from Puget Sound. Overall, our study provides an overview of the requirements and availability of prey for SRKW over the last 40 years, while supporting the hypothesis that SRKW were limited by prey abundance in the study period.

Nonstationary patterns in demographic traits covary with Chinook salmon marine distributions

The abundance of many Chinook salmon ( Oncorhynchus tshawytscha) stocks has declined despite reductions in harvest. We used state-space models parameterized with data from 57 Chinook salmon indicator stocks, ranging from coastal Oregon to southeast Alaska, to quantify long-term (since 1972 release year) changes in juvenile marine survival rate and mean age-at-maturity, as well as identify stock groupings with coherent dynamics. We found that juvenile marine distribution—rather than freshwater life history, run timing, or adult marine distribution—was the best predictor of trends in both survival and age. Only subyearling stocks that enter the Strait of Georgia showed evidence of transitioning to a low juvenile survival period, other groupings exhibited low and stable or cyclical patterns in survival. Conversely, declines in mean age-at-maturity were widespread and do not appear to have stabilized, suggesting that future declines in Chinook salmon population productivity may be influenced by earlier maturation or increased adult mortality, rather than further reductions in juvenile marine survival.

Effectiveness monitoring of juvenile Chinook salmon restoration projects in south Lake Washington, Washington State

Tabor RA, Liermann MC, Gearns HA, Moore ZJ, Lynch KD, Kurko K, Crittenden J, Shoemaker ME. 2022. Effectiveness monitoring of juvenile Chinook salmon restoration projects in south Lake Washington, Washington State. Lake Reserv Manage. 38:180–196. We evaluated 4 large restoration projects in south Lake Washington that were designed to improve nearshore habitat for lake-rearing juvenile Chinook salmon (Oncorhynchus tshawytscha). Restoration projects included shoreline modification, substrate enhancement, addition of engineered log jams (ELJs), and nonnatal tributary improvements. For most projects, we used a BACI (before-after-control-impact) study design. Projects were evaluated by determining the nighttime abundance of juvenile Chinook salmon through visual observations (primarily snorkeling with some surface observations in small nonnatal tributaries). Juvenile Chinook salmon are typically concentrated in the south end of the lake near their natal stream, and the project that was the farthest away from the natal stream did not appear to be beneficial, likely because few Chinook salmon were present. The highest observed abundance of juvenile Chinook salmon was associated with ELJs, where the abundance in February to April was typically 2 to 5 times higher than along adjacent, open shorelines. From January to April, juvenile Chinook salmon were usually more abundant in a daylighted nonnatal tributary (i.e., reconfigured from an unusable underground culvert to a more natural stream channel at the surface) than in 2 reference sites. Overall, all 4 project types improved juvenile use of the restored area, with substrate enhancement generally having the weakest response and ELJs the strongest response. Although most restoration projects for salmonids in the Pacific Northwest have focused on lotic systems, our results suggest projects in lentic systems may also be beneficial and should be considered by land-use managers. Supplemental data for this article is available online at https://doi.org/10.1080/10402381.2022.2027054 .

Spatial and Temporal Variability in Chinook Salmon Abundance Reflects Opportunity to Support Life History Diversity in an Estuarine Landscape

Spatial and Temporal Variability in Chinook Salmon Abundance Reflects Opportunity to Support Life History Diversity in an Estuarine Landscape

Identifying the potential of anadromous salmonid habitat restoration with life cycle models.

An investigation into the causes of species decline should include examination of habitats important for multiple life stages. Integrating habitat impacts across life stages with life-cycle models (LCMs) can reveal habitat impairments inhibiting recovery and help guide restoration efforts. As part of the final elements of the Habitat Restoration Planning model (HARP; Beechie et al. this volume), we developed LCMs for four populations of three species of anadromous salmonids (Oncorhynchus kisutch, O. tshawytscha, and O. mykiss), and ran diagnostic scenarios to examine effects of barrier removal, fine sediment reduction, wood augmentation, riparian shade, restoration of the main channel and bank conditions, beaver pond restoration, and floodplain reconnection. In the wood scenario, spawner abundance for all populations increased moderately (29–48%). In the shade scenario, spring-run Chinook salmon abundance increased the most (48%) and fall-run Chinook salmon and steelhead were much less responsive. Coho responded strongly to the beaver pond and floodplain scenarios (76% and 54%, respectively). The fine sediment scenario most benefitted fall- and spring-run Chinook salmon (32–63%), whereas steelhead and coho were less responsive (11–21% increase). More observations are needed to understand high fine sediment and its impacts. Our LCMs were region-specific, identifying places where habitat actions had the highest potential effects. For example, the increase in spring-run Chinook salmon in the wood scenario was driven by the Cascade Mountains Ecological Region. And, although the overall response of coho salmon was small in the barrier removal scenario (6% increase at the scale of the entire basin), barrier removals had important sub-regional impacts. The HARP analysis revealed basin-wide and regional population-specific potential benefits by action types, and this habitat-based approach could be used to develop restoration strategies and guide population rebuilding. An important next step will be to ground-truth our findings with robust empirically-based estimates of life stage-specific survivals and abundances.

Survival of the fattest: linking body condition to prey availability and survivorship of killer whales

AbstractRecovering small, endangered populations is challenging, especially if the drivers of declines are not well understood. While infrequent births and deaths may be important to the outlook of endangered populations, small sample sizes confound studies seeking the mechanisms underlying demographic fluctuations. Individual metrics of health, such as nutritive condition, can provide a rich data source on population status and may translate into population trends. We examined interannual changes in body condition metrics of endangered Southern Resident killer whales (SRKW) collected using helicopters and remotely operated drones. We imaged and measured the condition of the majority of all three social pods (J, K, and L) in each of seven years between 2008 and 2019. We used Bayesian multi‐state transition models to identify relationships between body condition changes and both tributary‐specific and area‐based indices of Chinook salmon abundance, and K‐fold cross‐validation to compare the predictive power of candidate salmon covariates. We found that Fraser River (tributary‐specific) and Salish Sea (area‐based) Chinook salmon abundances had the greatest predictive power for J Pod body condition changes, as well as the strongest relationships between any salmon covariates and SRKW condition across pods. Puget Sound (tributary‐specific) Chinook salmon abundance had the greatest predictive power for L Pod body condition changes, but a weaker relationship than Fraser River or Salish Sea abundance had with J Pod body condition. The best‐fit model for K Pod included no Chinook covariates. In addition, we found elevated mortality probabilities in SRKW exhibiting poor body condition (reflecting depleted fat reserves), 2–3 times higher than whales in more robust condition. Collectively, these findings demonstrate that (1) fluctuations in SRKW body condition can in some cases be linked to Chinook salmon abundance; (2) the three SRKW pods appear to have distinct patterns of body condition fluctuations, suggesting different foraging patterns; and (3) aerial photogrammetry is a useful early‐warning system that can identify SRKW at higher risk of mortality in the near future.

Legal Options (and Obligations?) for Enhanced Canada–United States Cooperative Southern Resident Killer Whale Conservation

The critically endangered Southern Resident killer whale (SRKW) population is at a conservation crossroads. The SRKW’s range extends from California to southern Alaska, but the core habitat of the species is the inland Salish Sea. The principal threats to the population are the decline in Chinook salmon abundance, physical and acoustic disturbance, and environmental contamination. Effective management must respond to the cumulative impact of these threats. The SRKW population has been protected as an endangered species in Canadian and U.S. waters for more than a decade, and emergency conservation measures have been produced in both jurisdictions. Unfortunately, these conservation measures have failed to stabilize the population or advance cooperative ecosystem-based conservation. The United Nations Convention on the Law of the Sea (UNCLOS) legally obligates states to cooperate in marine mammal conservation and, with respect to cetaceans, specifically requires states to work through an appropriate institution for their conservation and management. This article examines ongoing efforts by Canada and the United States to stabilize and recover the SRKW population in view of UNCLOS and the objective of long-term stewardship. This assessment includes ad hoc cooperative mechanisms and possible developments under existing cooperative forums. Although the base legal obligations created by UNCLOS are likely met, the objective of institutionalized cooperative cetacean conservation and management in UNCLOS is not met; moreover, existing cooperative forums are insufficient to effect SRKW recovery. Canada and the United States continue to approve projects without properly assessing the cumulative transboundary impact on the SRKW population or quantifying their contribution to important ecosystem-based thresholds, which reveals the true extent of management dissonance in the Salish Sea. This analysis concludes that enhanced bi-lateral cooperation and long-term co-existence with the SRKW population requires the creation of a new institutional forum, analogous to the International Joint Commission, that coordinates SRKW recovery measures and assesses future projects in view of cumulative effects management.

Fish distribution in a southern Patagonian river invaded by Chinook salmon

This study analysed the spatial–temporal abundance and distribution of exotic Chinook salmon (Onchorynchus tsawytscha) along the shore zone of the Lapataia River in relationship with the presence of non-native brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta), and native small puyen (Galaxias maculatus) during the four seasons of the year. These data were used to detect fish patchiness and spatial overlap and related to environmental characteristics to determine the habitat used by each species. Juvenile Chinook salmon was recorded only in spring and summer, showing a highly aggregated spatial distribution pattern. The native small puyen dominated fish assemblages all over the year, except in winter when brook trout showed the highest abundance. The highest overlap was detected between small puyen and Chinook salmon. Chinook salmon distribution was mainly explained by the occurrence of flood plains. Brown trout distribution was highly related to the presence of woody debris, while small puyen and brook trout showed no preferences for any environment. These results provide little evidence for habitat competition between Chinook salmon and the other native and non-native fish species. In contrast, species habitat preferences are likely shaping the current fish distribution.

A cumulative effects model for population trajectories of resident killer whales in the Northeast Pacific

Like numerous species at risk, the resident killer whale populations of the Northeast Pacific are vulnerable to the cumulative effects of anthropogenic threats. A Pathways of Effects conceptual model summarised the current understanding of each threat (prey availability, acoustic and physical disturbance, and contaminants), threat interactions, and potential impacts to fecundity and mortality. A Population Viability Analysis utilised the most recent available data to quantify impacts of threats on population parameters. The impacts of individual and cumulative threat scenarios on modelled Southern and Northern Resident Killer Whale populations were compared to the observed population demographics to define a model that best captured the real world dynamics. Of the individual and combined threat models tested, the cumulative model incorporating all threats predicted demographic rates closest to those observed for both populations. Recent low Chinook salmon abundance and its interactions with vessel disturbance and contamination strongly influenced modelled killer whale population dynamics. The cumulative effects population viability analysis model projected a mean increase in the modelled Northern Resident Killer Whale population to the carrying capacity within 25 years. In contrast, the mean modelled Southern Resident Killer Whale population trajectory was projected to decline under current conditions, with a 26% probability of population extinction, and in those projections, extinction was estimated to occur after 86 (± 11) years. Our results highlight the importance of considering the collective impact of multiple threats to imperilled species and the necessity of testing management and mitigation measures aimed at recovery using a holistic, validated model.

Qualitative and Quantitative Fisher Perceptions to Complement Natural Science Data for Managing Fisheries

Sustainably managing fisheries for ecological and social objectives in the current era of rapid environmental change requires that managers, scientists, and fishery stakeholders work together to find solutions to complex problems. Recognizing that multiple forms of knowledge generation exist and focusing on the strengths of different ways‐of‐knowing can facilitate a more holistic understanding of these problems. Here, we illustrate the value in both natural and social science‐generated information for informing our understanding of a rapidly changing social–ecological system. Using data collected through an in‐person and online survey, we show that methods for quantifying user perceptions can facilitate the integration of social data with traditional scientific data collection efforts. Specifically, the synthesis of a Bayesian lifecycle model (Cunningham et al. 2018) for Chinook Salmon Oncorhynchus tshawytscha and quantified fisher perceptions suggests that natural science efforts and resource users largely agree on many of the factors that may be contributing to the observed declines in abundance of Chinook Salmon in Alaska. A qualitative assessment of the perceptions of resource users revealed benefits to incorporating stakeholders in science and management, including the ability to identify regional issues or trends potentially unrealized by natural science approaches. Our study highlights the synergistic value of multiple sources of ecological information for sustainably managing fishery systems.

Surface behaviors correlate with prey abundance and vessels in an endangered killer whale (Orcinus orca) population

AbstractSouthern Resident killer whales (SRKWs) (Orcinus orca) are an endangered population in the United States and Canada, partly due to declines of their primary prey species, Chinook salmon. Prey availability influences various aspects of SRKW behavior, including distribution patterns and social structure. Yet, it is unclear to what extent a limited prey source influences the frequency of surface‐active behaviors (SABs), behaviors with important ecological implications. Here, we used long‐term datasets (1996–2019) to examine the relationships between the abundance of Chinook salmon, vessel presence, and the frequency with which SRKWs perform SABs. Salmon abundance was a significant predictor of SAB frequency, with fewer SABs performed in times of lower salmon abundance. SRKWs displayed more SABs when more whale watching vessels were present, and the whales spent a greater amount of time in the study area, performing more milling as opposed to traveling behavior, when vessel numbers were higher. Lastly, we found pod‐specific differences, such that K pod displayed significantly fewer SABs than either J or L pods. The observed relationships between SRKW behavior and both salmon abundance and vessel presence have implications for social network cohesion and foraging success. Our study adds to a growing body of literature highlighting factors affecting SRKW behavior as they experience increased threats from decreased prey availability, habitat loss, and anthropogenic disturbance, with implications for trans‐boundary management and conservation efforts.

AGE, SEX CLASS, AND PREY ABUNDANCE INFLUENCE THE FREQUENCY AND TYPE OF PERCUSSIVE BEHAVIOR IN THE SOUTHERN RESIDENT KILLER WHALE (ORCINUS ORCA) POPULATION AT LIME KILN POINT STATE PARK

The endangered Southern Resident Killer Whale (Orcinus orca, SRKW) is an iconic species in the Pacific Northwest. Although many ecological aspects of this population have been studied, why SRKW perform above-surface “percussive” behavior such as breaching, cartwheeling, pectoral-fin slapping, tail lobbing, and dorsal-fin slapping remains unclear. In the present study, we observed SRKW in Haro Strait, Washington, to evaluate trends in percussive behavior by age and sex class during the summer of 2016, and used long-term data (1996–2016) to compare the relationship between the seasonal frequency of percussive behaviors and the abundance of Chinook Salmon (Oncorhynchus tshawytscha) the primary food source of SRKW. Over the summer season in 2016, we documented 24 encounters involving percussive behavior. We found a significant difference between ages and sexes in the rate of percussive behaviors performed, with adult females performing the most behaviors among these groups, and tail slaps comprising the most frequent behavior performed. We also found a significant positive relationship between the rate of percussive behaviors and Chinook Salmon abundance in the Salish Sea over the past 2 decades. These findings present a preliminary investigation into the potential for behavioral observations to serve as indicators of population-level health or behavioral trends, which could be important for this population's conservation.

Relationship between per capita births of Cook Inlet belugas and summer salmon runs: age‐structured population modeling

AbstractAnthropogenic disturbances may alter a population's conservation status if the ability of individuals to survive and breed is affected. We used an adaptation of the Heligman‐Pollard model to estimate survival at age of Cook Inlet belugas (CIB; Delphinapterus leucas), an endangered population in south‐central Alaska. We developed an age‐structured Leslie matrix model, based on the life history parameters survival and fecundity probability, to evaluate the sensitivity of population size and growth of CIB, to variation in estimate values of Chinook and coho salmon abundance in the Deshka River, a major tributary of the Susitna River. Birth effect (eb) was regressed against Chinook and coho salmon levels for the year of, the year before, and two years before a beluga calf birth. The effect of a range of modifications of salmon availability was illustrated in CIB with a series of simulations. The maximum annual population growths (λ) were set at 1.036 (3.6%). Ranges of CIB survival and fecundity probabilities indicated small changes in survival probabilities have a greater impact on population growth than similar changes in birth probability. As either survival (es) or fecundity (eb) was reduced, the annual growth declined, with either es = 0.961 or eb = 0.388, causing a decreased annual growth of −0.4%. Regressions of Chinook salmon for the year of, the year before, and two years before a birth were all significant at the 5% level as was coho in the year of and year prior to birth. The mechanism model with the best fit was the sum of Chinook and coho in the year of birth and year prior to birth. Simulations showed that if salmon runs remained at their current levels, the CIB population would likely continue its current slow decline and per capita births would continue to be low. The results from this study suggest reproductive success in CIB is tied to salmon abundance in the Deshka River. Current management practices should consider this when setting research priorities, designing new studies, and developing management actions to achieve CIB population recovery targets.

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.

Stock specific relative abundance of Columbia River juvenile Chinook salmon off the Southeast Alaska coast

Migration patterns of juvenile Columbia River Chinook salmon (Oncorhynchus tshawytscha) differ among stocks and life history types, creating diverse marine distributions of these fish. This results in different stocks being subject to different ocean conditions during their first summer of marine residence, a time that is critical for their survival. Understanding their early marine distributions, and the conditions that affect their survival, may enhance conservation efforts for these stocks, many of which are protected under the Endangered Species Act. We analyzed juvenile Chinook salmon samples collected in trawls made from 2011 to 2015 off the southeastern (SE) Alaskan panhandle, and off the coasts of Washington and Oregon. We used genetic stock identification techniques to estimate stock proportions of juvenile Chinook salmon in each of these areas. Results indicated that most juvenile Chinook salmon in our SE Alaska coast study area in July originate from Columbia River spring-run stocks. We found a significant relationship in catch per unit effort (CPUE) over all stocks between the SE Alaska and the Washington and Oregon coast samples. In 2011, CPUE for Columbia River spring-run stocks for the SE Alaska coast was lower than for the Washington and Oregon coast, suggesting a differing level of marine mortality that year. We also found a significant relationship between juvenile CPUE of interior Columbia River spring-run stocks off the SE Alaska coast and adult counts at Bonneville Dam two years later. Our results provide marine life history, performance and survival information that supports management and recovery efforts for Columbia River Chinook salmon.