Download or read book Potential Causes of Size Trends in Yukon River Chinook Salmon Populations written by and published by . This book was released on 2006 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: Concerns regarding the size and sex composition of Yukon River Chinook salmon, Oncorhynchus tshawytscha, have been expressed in public meetings for over a decade. However, reports of small size and low numbers of females have become increasingly common in recent years, and apprehension over the long-term health of the stock has grown within the drainage. In response to these reports, the Salmon Size Subcommittee of the US/Canada Yukon River Joint Technical Committee was formed and charged with advising the Committee, and thereby the US/Canada Yukon River Panel, with respect to changes in chinook salmon age, sex, and size composition. This report, which summarizes the findings of prior investigations and the scientific literature on factors that influence salmon morphology, represents the first product of the subcommittee.

Download or read book Chinook Salmon Age Sex and Length Analysis from Selected Escapement Projects on the Yukon River written by Karen Hyer and published by . This book was released on 2005 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt: Anecdotal information from fishers along the Yukon River suggests that the length of chinook salmon harvested and the proportion of female Chinook salmon in the run have decreased over time. To determine whether sex composition, size, age, and size-at-age of chinook salmon in spawning escapements have experienced a basin-wide decline over time, we examined escapement data from the Andreafsky, Anvik, Gisasa, Salcha, Chena, and Big Salmon Rivers. The scope of the analysis is limited to a relatively small number of spawning tributaries over a relatively short time period during which both fisheries and environmental changes have occurred confounding the ability to establish the sources of the decreasing size trend in Yukon River Chinook salmon.

Download or read book Exploring the Potential Role of Late Stage Predation and Chinook Salmon Age Structure written by Kaitlyn A. Manishin and published by . This book was released on 2018 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chinook salmon (Oncorhynchus tshawytscha) populations across the North Pacific have displayed a decrease in body size-at-return resulting from declines both in age- and body size-at-maturity. These changes have precipitated the loss of the oldest age classes in some populations and have occurred throughout the range of this species, suggesting a shared – yet currently unknown – driver in the common marine environment. A hypothesis for the cause of these changes is intense and/or selective predation marine mortality after the first winter in the ocean, potentially from predators selectively removing relatively large sub-adult Chinook salmon. Here I consider the question: under what circumstances could predation on large sub-adult individuals by salmon sharks (Lamna ditropis) change the age structure of a Chinook salmon population? To address this question, I first estimated total per capita prey consumption by salmon sharks – an increasingly acknowledged predator of salmon on the high seas – using three methods: 1) daily ration requirement, 2) bioenergetic mass balance, 3) and a von Bertalanffy growth model. Second, I examined the effects of additional predation on an indicator Chinook salmon population from the Yukon River by simulating alternative predation scenarios with a stage-structured life cycle model. Scenarios described the strength and selectivity of predation, and the resulting simulated age structure was then compared to observed demography. The selectivity and intensity of removals required to produce this change in age structure were considered in the context of top predators, focusing on salmon sharks. The daily ration method yielded individual salmon shark consumption estimates of 1461 and 2202 kg·yr-1, the mass-balance method produced estimates of 1870 kg·yr-1, 2070 kg·yr-1, 1610 kg·yr-1, and 1762 kg·yr-1, depending on assumed diet, and the growth model output estimates of 16,900 kg·yr-1 or 20,800 kg·yr-1, depending on assumed assimilation efficiency. The per capita prey consumption estimates from the mass-balance method may be the most realistic because they incorporated life history data specific to salmon sharks and did not produce extreme values. Taken as a whole, these estimates suggest salmon sharks have energetic requirements similar to those of piscivourous marine mammals and corroborates conclusions of previous research suggesting that endothermic fishes exhibit metabolic rates similar to marine mammals. The simulated mortality scenarios that most closely mimicked observed shifts in age structure of the indicator Chinook salmon population focused intense and selective predation on the third year of Chinook salmon residence in the ocean. This simulated predation is corroborated by emerging results from an independent electronic tagging study in which tagged Chinook salmon experienced high predation rates, and research suggesting that killer whales (Orcinus orca) selectively prey upon Chinook salmon in their third year at sea. In summary, salmon sharks likely have high energetic requirements that could result in a large biomass of prey consumed, Chinook salmon populations are sensitive to predation during the third ocean year, and salmon sharks and other predators appear to frequently consume fish at that ocean stage. Taken together, these lines of evidence point to a potentially important mechanism for top down pressure on Chinook salmon populations that may explain observed changes in age-at-return, which in turn can affect population productivity. Future work and more robust data on predator distributions and abundances are needed to explore this finding further.

Download or read book Yukon River Chinook Salmon Comparative Mesh Size Study written by Kathrine G. Howard and published by . This book was released on 2010 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gillnet mesh size in the Yukon River Chinook salmon fishery has been unrestricted, leading many to believe that the fishery is size selective. The presented study used a test fishery in Yukon River District 1 near Emmonak to investigate catch composition of 7, 7.5, and 8-inch stretch-mesh drift gillnets. Age, sex, length, weight and girth (ASLWG) characteristics of Chinook salmon, and the species composition of the catch were examined. Comparisons among mesh sizes and with temporally congruent data from Lower Yukon River commercial and other test fisheries are included. Overall patterns indicate that larger mesh sizes catch a greater proportion of older fish, more Chinook relative to chum salmon, a greater proportion of females, and more larger fish with respect to length, weight and girth. This study provides important insight for management strategies and regulations concerning mesh size for Yukon River fisheries, as well as improves our understanding of potential effects of size-selective fishing.

Download or read book Changes in Size and Age at Maturity of Columbia River Upriver Bright Fall Chinook Salmon Oncorhynchus Tshawytscha written by Roy E. Beaty and published by . This book was released on 1992 with total page 540 pages. Available in PDF, EPUB and Kindle. Book excerpt: The average size and age of chinook salmon (Oncorhynchus tshawytscha) caught in commercial fisheries along the Pacific Coast of North America have decreased substantially in this century. These declines might be caused in part by changes in size and age at maturity within the stocks contributing to those fisheries. Upriver Brights (Brights), a stock of fall chinook salmon in the Columbia River, are one of those stocks. The purposes of this study were to (1) determine if average size and age at maturity of Brights have declined, (2) gain a better understanding of the factors that may contribute to such declines, and (3) describe potential consequences of these changes. Data from in-river fisheries suggest that the average weight of mature Brights returning to the Columbia River has decreased approximately 2.7 kg since the 1910s, an average rate of about 0.1 lb·yr−1 (45 g·yr−1). Most of the potential biases in these data tend to make this estimate conservative. Insufficient data were available to describe changes in average age at maturity. There are many potential causes for the decline in average size of mature Brights, including factors that affect very early life stages. Other researchers have determined that size at maturity appears to be highly influenced by inheritance, gender, and growth rate. I describe how maternal size can influence -- through time of spawning, choice of spawning site, and egg size -- the viability of the young, which carry the dam's genes for size. The size-related ability to produce viable offspring may have been changed by modifications in the environment. Very little is known about how changes in the natural environment for spawning, incubation, and rearing may have contributed to a decline in average size at maturity. Artificial propagation and rearing, such as at Priest Rapids Hatchery, seems to produce adult Brights that are smaller, younger, and more likely to be male than their natural counterparts. The net result is that the average hatchery fish may have only about 0.80 of the reproductive potential of the average natural fish. Changes in growth conditions in the ocean probably did not contribute to the change in size, although the ocean fisheries of Southeast Alaska and British Columbia appear to select, in the genetic sense, against large size and old age in Brights. Since 1978, in-river commercial fisheries have caught larger Brights and a higher proportion of females than are found in the escapement of the Priest Rapids Hatchery component of the stock, but the fisheries impact the two sexes differently by taking the larger males and the smaller females. The effect on the natural component may differ because of their apparently larger average size. I found no evidence that larger fish or more females were caught when 8-in. minimum restrictions were in effect on gillnet mesh size relative to periods when mesh size was not restricted. Impounding the mainstem during the last 50+ yr may have removed obstacles to migration (e.g., Celilo Falls) that selected for large size in Brights, but that hypothesis could not be tested. The perserverance of larger and older phenotypes in the Bright stock suggests that countervailing selection -- perhaps during spawning, incubation, and/or early rearing -- may have resisted the effects of a century of size- and age-selective fisheries. That resistance, however, may reduce the productivity of the stock. Declines in average size and age at maturity can have undesireable consequences. Lower average size means less biomass landed and lower commercial value. Lower average fecundity and a diminished ability to reproduce in some environments are also expected. Loss of size and age classes may reduce the ability of the stock to adapt to environmental variations. These results are relevant to several management practices. A holistic approach to fishery management issues is necessary to avoid erroneous conclusions based on narrow perspectives. Measuring reproductive potential of the catch and escapement would be superior to the conventional practice of simply counting numbers of fish. Many aspects of artificial propagation can be improved, including broodstock aquisition, mating regimes, and rearing practices. Stock abundance is a major factor in determining the effect of many management practices on the stock. In general, fisheries managers must be mindful that they manage very complex natural systems.

Download or read book Size and Scale Characteristics of Upper Yukon River Juvenile Chinook Salmon Oncorhynchus Tschawytscha written by and published by . This book was released on 1990 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chinook salmon migrate seaward either during their first spring and summer (ocean-type) or after one or two years in freshwater (stream-type). The tendency to remain a year or longer in freshwater is determined by the harshness of the rearing environment. Salmonids reared in severe environments with short growing seasons may not develop an annulus on their scale at the end of the first growing season. This paper compares circulus counts and size among 15 upper Yukon River tributary populations of juvenile chinook salmon collected in late August 1987 and between May 26 and August 20 in 1988 and examines the timing of freshwater annulus formation.

Download or read book Influence of Freshwater Processes on Juvenile Chinook Salmon Size Movement and Outmigration Timing in the Chena River Alaska written by Olivia N. Edwards and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chinook Salmon Oncorhynchus tshawytscha have experienced population declines across their range in recent decades, including Alaska where they are a critical subsistence, commercial, and sport fish species. The Alaska Board of Fisheries has listed Yukon River Chinook salmon as a “stock of yield concern” since 2000 prompting the implementation of escapement goals for key spawning tributaries in 2001. Additionally, research efforts across the basin have increased to better understand potential mechanisms behind these declines and provide information to facilitate management decisions. To help fill a critical data gap in the overall understanding of the fishery, this research investigated various freshwater juvenile life history factors including patterns in post-emergence summer body size, movement, and fish size during spring outmigration in the Chena River, Alaska. This research also identified links between these biological factors and freshwater processes that are affected by climate change, including stream temperature and discharge, with the intention of documenting benchmark information as conditions continue to change. Juvenile Chinook Salmon movement among four key rearing areas was observed during summer and fall 2019 and early spring 2020. Despite differences in early summer size patterns, by the end of September mean fork lengths were not statistically different among all rearing areas (ANOVA; all P > 0.05). Additionally, mean September weight varied among six years of empirical data and ranged from 3.19 g in 2018 (0.03 SE) to a maximum of 5.10 g in 2009 (0.05 SE). September weight was simulated across years with variable stream temperatures and discharge (2003 to 2020) using a bioenergetics model, and compared to observed data. Weight simulations were within

Download or read book New 3 d Video Methods Reveal Novel Territorial Drift feeding Behaviors that Help Explain Environmental Correlates of Chena River Chinook Salmon Productivity written by Jason Neuswanger and published by . This book was released on 2014 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chinook salmon (Oncorhynchus tshawytscha) are critical to subsistence and commerce in the Yukon River basin, but several recent years of low abundance have forced devastating fishery closures and raised urgent questions about causes of the decline. The Chena River subpopulation in interior Alaska has experienced a decline similar to that of the broader population. To evaluate possible factors affecting Chena River Chinook salmon productivity, I analyzed both population data and the behavior of individual fish during the summer they spend as fry drift feeding in the river. Using a stereo pair of high definition video cameras, I recorded the fine-scale behavior of schools of juvenile Chinook salmon associated with woody debris along the margins of the Chena River. I developed a software program called VidSync that recorded 3-D measurements with sub-millimeter accuracy and provided a streamlined workflow for the measurement of several thousand 3-D points of behavioral data (Chapter 1). Juvenile Chinook salmon spent 91% of their foraging attempts investigating and rejecting debris rather than capturing prey, which affects their energy intake rate and makes foraging attempt rate an unreliable indicator of foraging success (Chapter 2). Even though Chinook salmon were schooling, some were highly territorial within their 3-D school configurations, and many others maintained exclusive space-use behaviors consistent with the population regulatory effects of territoriality observed in other salmonids (Chapter 3). Finally, a twenty-year population time series from the Chena River and neighboring Salcha River contained evidence for negative density dependence and a strong negative effect of sustained high summer stream discharge on productivity (Chapter 4). The observed territoriality may explain the population's density dependence, and the effect of debris on foraging efficiency represents one of many potential mechanisms behind the negative effect of high stream discharge. In combination, these findings contribute to a statistically and mechanistically plausible explanation for the recent decline in Chena River Chinook salmon. If they are, in fact, major causes of the decline (other causes cannot be ruled out), then we can be tentatively hopeful that the population may be experiencing a natural lull in abundance from which a recovery is possible.

Download or read book Factors Affecting the Abundance of Fall Chinook Salmon in the Columbia River written by Jack M. Van Hyning and published by . This book was released on 1968 with total page 848 pages. Available in PDF, EPUB and Kindle. Book excerpt: A study of the population ecology of Columbia River fall chinook salmon, Oncorhynchus tshawytscha (Walbaum), was made in an attempt to determine the cause of a serious decline in this run which occurred in the early 1950's. Fluctuations in abundance of major salmon runs the North Pacific were examined to detect any coastwide pattern. Only chinook salmon in Cook Inlet, Alaska, and chum salmon from Oregon to southwestern Alaska showed a similar trend. The following life history stages broken down into pre- and post-decline years were examined: (1) marine life including distribution and migration, growth and maturity, survival rate, oceanography, and commercial and sport fisheries; (2) upstream migration including river fisheries, gear selectivity, size and age composition of the run, escapement, and influence of dams, diseases, and water quality; (3) reproduction and incubation including spawning areas and spawning and incubation conditions; and (4) downstream migration which included predation, dams and reservoirs, diseases, flow, turbidity and temperature, and estuary life. Salient points of the analysis were: (1) a change in the maturity and survival pattern based on tagged and fin-clipped fish recovered before and after 1950; (2) a significant negative correlation between sea-water temperature during a year class' first year at sea and subsequent survival; (3) a large increase in the ocean fisheries coincident with the decline in the run; (4) catch-effort statistics of the ocean fishery show a near classic example of the effect of overexploitation; (5) estimates of the contribution of Columbia River chinook to the ocean fisheries based on tag recoveries could be underestimates rather than overestimates; (6) a significant inverse correlation between estimated ocean catch of Columbia River fall chinook and numbers entering the river; (7) size and age composition of the ocean and river catches decreased coincident with the decline in the run; (8) the gill-net fishery shows little size selectivity by age, size, or sex in the dominant group; (9) fluctuations in abundance of hatchery stocks are related to differences in survival between fingerling and adult; (10) hatchery, lower river, and upriver populations fluctuate in abundance in much the same pattern; (11) optimum escapement is between 90,000 and 100,000 adults, a value that was exceeded during most years; (12) a highly significant negative correlation between numbers of spawners and return per spawner; (13) most of the early dams had no direct effect on fall chinook and the decline in productivity occurred when river conditions were relatively stable; (14) temperatures at time of migration and spawning for fall chinook have not increased enough to be a serious mortality factor; (15) little relationship between flow, turbidity, and temperature at time of downstream migration and subsequent return was evident except that high temperatures and high flows (and turbidities) tended to produce poorer runs during certain time periods; and (16) predation and delay of smolts in reservoirs are largely unknown factors, but circumstantial evidence suggests that they were not important in regulating fall chinook numbers during the period of the study. Finally, variables that appeared to bear some relationship to fluctuations in abundance of fall chinook were submitted to multiple regression analysis. For the predecline period (1938-46 brood years), sea-water temperature and ocean troll fishing effort were significant variables (R2 = 0.74). For post decline years (1947-59 broods), troll had the most influence on total return with ocean temperature and escapement having lesser effects. For the combined years, troll intensity and ocean temperature were the significant variables (R2 = 0.572). Entering interaction of river flow at downstream migration with the other variables brought R2 to 0.754 which means that 75% of the variability in the returning run could be accounted for by these three factors. Return per spawner was so heavily influenced by numbers of spawners that the other factors assumed negligible importance. Equations were derived that predicted the returning run in close agreement with the actual run size. Substituting a low and constant troll fishing effort in the equation resulted in the predicted run maintaining the average predecline level. The increase in ocean fishing was the main contributor to the decline of the Columbia River fall chinook run as shown by correlation, by analogy, and by the process of elimination. To demonstrate why other chinook runs have not shown similar declines, it was shown that due to several unique features in Columbia River fall chinook life history they are exposed to much more ocean fishing than other populations. It was emphasized that these conclusions should not be extrapolated to the future or to other species or runs of salmon.

Download or read book An Investigation of the Potential Effects of Selective Exploitation on the Demography and Productivity of Yukon River Chinook Salmon written by Jeffrey F. Bromaghin and published by . This book was released on 2008 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: A study on how selective exploitation of large fish leads to widespread and undesirable changes to productivity, demographic composition, and reduction of genetic variation, such as altering size and age distributions of breeding adults. This study focused on effects due to fish take through large-mesh gill netting.

Download or read book Size and Scale Characteristics of Upper Yukon River Juvenile Chinook Salmon Oncorhynchus Tschawytscha written by Henderson, Michael A and published by Nanaimo, B.C., Canada : Fisheries and Oceans, Canada. This book was released on 1990 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Forecasting Stock specific Upriver Migration Timing of Chinook Salmon in the Yukon River written by Bryce Douglas Mecum and published by . This book was released on 2016 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pacific salmon (Oncorhynchus spp.) are an economically and culturally important genus of fishes endemic to the North Pacific. Their sustainable management depends on an understanding of the drivers of their abundance and migration dynamics. In many instances, statistical models are employed to predict abundance and run timing before harvest takes place to more effectively meet management objectives. In this thesis, I created a general-purpose predictive model of run timing that can be applied to many salmon populations. I then applied it to Yukon River Chinook salmon (O. tshawytscha) by generating pre-season predictions of inriver run timing, which I then compared with existing observations of run timing at two upriver locations. Prediction errors were low enough for the model to be useful to management. Models such as the one created in this study represent an objective tool that can be used to reduce subjectivity in fisheries management.

Download or read book Determinants of Life History Variability in the Chinook Salmon Oncorhynchus Tshawytscha of Western Alaska written by Jared E. Siegel and published by . This book was released on 2017 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chinook Salmon from western Alaska have experienced recent declines in abundance, size, and age at maturity. Declines have led to hardships for the region's dependent subsistence and commercial users. Thus there is a managerial need to better understand factors effecting life-history expression in these populations. I used retrospective scale analysis and run reconstructions to investigate the causes of declines in age at maturity and the effect of the marine environment on growth, maturation, and survival in two western Alaskan Chinook Salmon populations subject to long-term monitoring: the East Fork Andreafsky River and the Kogrukluk River (tributaries of the Yukon River and Kuskokwim River respectively). The expression of age at maturation exhibited sex-specific responses to variability in growth. Additionally, thresholds for maturation, as described by a newly presented measure of maturation reaction norms that accounts for growth history, were found to have declined in both sexes. This can be interpreted as indirect evidence that observed declines in age at maturity represent an evolutionary response. I also found that sea surface temperatures in the Bering Sea exert strong control on the expression of life history variability. Warmer sea surface temperatures appear to lead to a younger age at maturity, largely through the vector of augmented growth. However, warmer sea surface temperatures additionally appeared to decrease the average age of male recruits by lowering growth thresholds for early male maturation. Despite the demonstrated relationship between Bering Sea surface temperatures and age at maturation, a lack of a temporal trend in sea surface temperatures during the period of analysis (1977-2013) suggests that temperature alone cannot explain documented declines in average age. However, this result suggests that the average age at maturation of western Alaskan Chinook Salmon will continue to decline with future predicted warming of the Bering Sea as a consequence of climate change.

Download or read book Yukon River Chinook Salmon Genetic Baseline written by William D. Templin and published by . This book was released on 2006 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report presents the results of a survey of 13 microsatellite loci (from a standardized set used by the Pacific Salmon Commission Chinook Technical Committee) in 2646 individual fish representing 11 U.S. Chinook salmon populations.

Download or read book Growth and Degree of Maturity of Chinook Salmon in the Ocean written by Willis Horton Rich and published by . This book was released on 1925 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Biological Opinion that Address the Potential Effects on Sacramento River Winter run Chinook Salmon from the Bureau of Reclamation s Proposed Los Vaqueros Project written by and published by . This book was released on 1993 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Stock specific Run and Escapement of Yukon River Chinook Salmon 1981 2019 written by Toshihide Hamazaki and published by . This book was released on 2021 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes a modeling framework to reconstruct the historical time series of drainagewide and stock-specific run and escapement of Pacific salmon Oncorhynchus spp. that return to a single large river system. The model combines historical data from various assessment projects that estimate mainstem passage, harvests, tributary escapements, and stock proportions under a single maximum-likelihood estimation framework. As a demonstration, the modeling framework was applied to reconstruct the historical (1981–2019) drainagewide run size and escapement of Yukon River Chinook salmon (O. tshawytscha) and each of the contributing stock components: Canada, Middle Yukon, and Lower Yukon. The model estimated that the average drainagewide (all stocks) run size was 301,000 (range: 109,000–491,000), escapement was 186,000 (88,000–305,000), and harvest rate was 35% (2–60%). The average Canada stock run size was 125,000 (39,000–214,000), escapement was 60,000 (14,000–126,000), and harvest rate was 48% (2–78%). The average Middle Yukon stock run size was 75,000 (22,000–139,000), escapement was 47,000 (14,000–126,000), and harvest rate was 35% (2–85%). The average Lower Yukon stock run was 101,000 (48,000–204,000), escapement was 78,000 (30,000–164,000), and harvest rate was 21% (1–51%). The next steps regarding the application of this model to Yukon River Chinook salmon should include a comprehensive data review, consideration of alternative model structures, and critical evaluation of model assumptions.