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Sewall Fletcher - One of the best experts on this subject based on the ideXlab platform.
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Pacific Herring Juvenile Winter Survival and Recruitment in Prince William Sound
University of Alaska Fairbanks, 2020Co-Authors: Sewall FletcherAbstract:Small pelagic fish abundances can vary widely over space and time making them difficult to forecast, partially due to large changes in the number of individuals that annually recruit to the spawning population. Recruitment fluctuations are largely driven by variable early life stage survival, particularly through the first winter for cold temperate fishes. Winter survival may be influenced by juvenile fish size, energy stores, and other factors that are often poorly documented, which may hamper understanding recruitment processes for economically and ecologically important marine species. The goal of this research was to improve understanding of recruitment of Pacific herring (Clupea pallasii) within Prince William Sound (PWS) through recruitment modeling and by identifying factors influencing winter survival of young-of-the-year (YOY) herring. Towards this end, my dissertation addresses three specific objectives: 1) incorporate oceanographic and biological variables into a herring recruitment model, 2) describe patterns in growth and condition of PWS YOY herring and their relationship to winter mortality risks, and 3) compare the growth, condition, swimming performance, and mortality of YOY herring that experience different winter feeding levels. In the recruitment modeling study, annual mean numbers of PWS herring recruits-per-spawner were positively correlated with YOY walleye pollock (Gadus chalcogrammus) abundance in the Gulf of Alaska, hence including a YOY pollock index within a standard Ricker model improved herring recruitment estimates. Synchrony of juvenile herring and pollock survival persisted through the three-decade study period, including the herring Stock Collapse in the early 1990s. While the specific mechanism determining survival is speculative, size-based tradeoffs in growth and energy storage in PWS YOY herring indicated herring must reach a critical size before winter, presumably to reduce size-dependent predation. Large herring switched from growth to storing energy, and ate more high-quality euphausiid prey, which would delay the depletion of lipid stores that compelled lean herring to forage. Lipid stores were highest in the coldest year of the seven-year field study, rather than the year with the best diets. With diets controlled in a laboratory setting, spring re-feeding following restricted winter diets promoted maintenance of size and swimming ability, but had little effect on mortality rates compared to fish continued on restricted rations. Declines in gut mass, even among fully fed herring, and low growth potential suggest limited benefits to winter feeding. Mortalities due to food restriction compounded by disease were highest among herring that fasted through winter months, and among small herring regardless of feeding level. Taken together, these findings illustrate the importance of achieving a critical size and high lipid stores in the critical period before winter to promote YOY herring winter survival and ultimately recruitment
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Pacific herring juvenile winter survival and recruitment in Prince William Sound
2020Co-Authors: Sewall FletcherAbstract:Thesis (Ph.D.) University of Alaska Fairbanks, 2020Small pelagic fish abundances can vary widely over space and time making them difficult to forecast, partially due to large changes in the number of individuals that annually recruit to the spawning population. Recruitment fluctuations are largely driven by variable early life stage survival, particularly through the first winter for cold temperate fishes. Winter survival may be influenced by juvenile fish size, energy stores, and other factors that are often poorly documented, which may hamper understanding recruitment processes for economically and ecologically important marine species. The goal of this research was to improve understanding of recruitment of Pacific herring (Clupea pallasii) within Prince William Sound (PWS) through recruitment modeling and by identifying factors influencing winter survival of young-of-the-year (YOY) herring. Towards this end, my dissertation addresses three specific objectives: 1) incorporate oceanographic and biological variables into a herring recruitment model, 2) describe patterns in growth and condition of PWS YOY herring and their relationship to winter mortality risks, and 3) compare the growth, condition, swimming performance, and mortality of YOY herring that experience different winter feeding levels. In the recruitment modeling study, annual mean numbers of PWS herring recruits-per-spawner were positively correlated with YOY walleye pollock (Gadus chalcogrammus) abundance in the Gulf of Alaska, hence including a YOY pollock index within a standard Ricker model improved herring recruitment estimates. Synchrony of juvenile herring and pollock survival persisted through the three-decade study period, including the herring Stock Collapse in the early 1990s. While the specific mechanism determining survival is speculative, size-based tradeoffs in growth and energy storage in PWS YOY herring indicated herring must reach a critical size before winter, presumably to reduce size-dependent predation. Large herring switched from growth to storing energy, and ate more high-quality euphausiid prey, which would delay the depletion of lipid stores that compelled lean herring to forage. Lipid stores were highest in the coldest year of the seven-year field study, rather than the year with the best diets. With diets controlled in a laboratory setting, spring re-feeding following restricted winter diets promoted maintenance of size and swimming ability, but had little effect on mortality rates compared to fish continued on restricted rations. Declines in gut mass, even among fully fed herring, and low growth potential suggest limited benefits to winter feeding. Mortalities due to food restriction compounded by disease were highest among herring that fasted through winter months, and among small herring regardless of feeding level. Taken together, these findings illustrate the importance of achieving a critical size and high lipid stores in the critical period before winter to promote YOY herring winter survival and ultimately recruitment.Exxon Valdez Oil Spill Trustee Council, NOAAGeneral Introduction -- Chapter 1. Empirically based models of oceanographic and biological influences on Pacific Herring recruitment in Prince William Sound -- Chapter 2. Growth, energy storage, and feeding patterns reveal winter mortality risks for juvenile Pacific herring in Prince William Sound, Alaska, USA -- Chapter 3. Condition and performance of juvenile Pacific herring with different winter feeding rations -- General conclusions
Sturla Furunes Kvamsdal - One of the best experts on this subject based on the ideXlab platform.
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stochastically induced critical depensation and risk of Stock Collapse
Marine Resource Economics, 2015Co-Authors: Diwakar Poudel, Leif Kristoffer Sandal, Sturla Furunes KvamsdalAbstract:This article investigates the risk of Stock Collapse due to stochastically induced critical depensation in managed fisheries. We use a continuous-time surplus production model and an economic model with downward-sloping demand and Stock-dependent costs. First, we derive an optimal exploitation policy as a feedback control rule by applying the Hamilton-Jacobi-Bellman approach and analyze the effects of stochasticity on the optimal policy. Then, we characterize the long-term sustainable optimal state and estimate the risk of Stock Collapse due to stochastically induced critical depensation. We find that the optimal harvest policy in the stochastic setting is conservative at low stochasticity and approaches the myopic solution at high stochasticity. The risk of Stock Collapse is increasing with the stochasticity and decreasing with Stock sizes.
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analyzing risk of Stock Collapse in a fishery under stochastic profit maximization
2012Co-Authors: Diwakar Poudel, Leif Kristoffer Sandal, Sturla Furunes KvamsdalAbstract:In commercial fisheries, Stock Collapse is an intrinsic problem caused by overexploitation or due to pure stochasticity. To analyze the risk of Stock Collapse, we apply a relatively simple Monte Carlo approach which can capture complex Stock dynamics. We use an economic model with downward sloping demand and Stock dependent costs. First, we derive an optimal exploitation policy as a feedback control rule and analyze the effects of stochasticity. We observe that the stochastic solution is more conservative compared to the deterministic solution at low level of stochasticity. For moderate level of stochasticity, a more myopic exploitation is optimal at small Stock and conservative at large Stock level. For relatively high stochasticity, one should be myopic in exploitation. Then, we simulate the system forward in time with the optimal solution. In simulated paths, some Stock recovered while others Collapsed. From the simulation approach, we estimate the probability of Stock Collapse and characterize the long term stable region.
Kenneth Patterson - One of the best experts on this subject based on the ideXlab platform.
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fisheries for small pelagic species an empirical approach to management targets
Reviews in Fish Biology and Fisheries, 1992Co-Authors: Kenneth PattersonAbstract:Long-term management targets based on MSY, Fmax or F0.1 are inappropriate for small pelagic fish because of the possibility of Stock Collapse owing to a Stock-recruit relationship at low biomasses. Better reference points such as Fmed and Fhigh that take account of Stock and recruit data cannot be used in developing fishery situations because they are too demanding of data. A simple model was fitted to medium-term (about 10 year) periods in exploited small pelagic fisheries, relating change in Stock biomass to exploitation rate. Data from 28 Stocks and 11 species were used. The fitted model was used to estimate likelihood of Stock decrease at different exploitation rates. The pelagic Stocks included in the model appeared to be in equilibrium for an exploitation rate F/Z=0.4, which may be used as a guideline for the appropriate exploitation of pelagic Stocks.
Diwakar Poudel - One of the best experts on this subject based on the ideXlab platform.
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stochastically induced critical depensation and risk of Stock Collapse
Marine Resource Economics, 2015Co-Authors: Diwakar Poudel, Leif Kristoffer Sandal, Sturla Furunes KvamsdalAbstract:This article investigates the risk of Stock Collapse due to stochastically induced critical depensation in managed fisheries. We use a continuous-time surplus production model and an economic model with downward-sloping demand and Stock-dependent costs. First, we derive an optimal exploitation policy as a feedback control rule by applying the Hamilton-Jacobi-Bellman approach and analyze the effects of stochasticity on the optimal policy. Then, we characterize the long-term sustainable optimal state and estimate the risk of Stock Collapse due to stochastically induced critical depensation. We find that the optimal harvest policy in the stochastic setting is conservative at low stochasticity and approaches the myopic solution at high stochasticity. The risk of Stock Collapse is increasing with the stochasticity and decreasing with Stock sizes.
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analyzing risk of Stock Collapse in a fishery under stochastic profit maximization
2012Co-Authors: Diwakar Poudel, Leif Kristoffer Sandal, Sturla Furunes KvamsdalAbstract:In commercial fisheries, Stock Collapse is an intrinsic problem caused by overexploitation or due to pure stochasticity. To analyze the risk of Stock Collapse, we apply a relatively simple Monte Carlo approach which can capture complex Stock dynamics. We use an economic model with downward sloping demand and Stock dependent costs. First, we derive an optimal exploitation policy as a feedback control rule and analyze the effects of stochasticity. We observe that the stochastic solution is more conservative compared to the deterministic solution at low level of stochasticity. For moderate level of stochasticity, a more myopic exploitation is optimal at small Stock and conservative at large Stock level. For relatively high stochasticity, one should be myopic in exploitation. Then, we simulate the system forward in time with the optimal solution. In simulated paths, some Stock recovered while others Collapsed. From the simulation approach, we estimate the probability of Stock Collapse and characterize the long term stable region.
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analyzing risk of Stock Collapse in a fishery under stochastic growth model
2012Co-Authors: Diwakar PoudelAbstract:Acknowledging that there is stochasticity in the dynamics of a fish Stock, one has a situation where the fish Stock can Collapse even without any fishing pressure. To derive the probability of Collapse, we suggest a Monte Carlo approach because it is relatively simple model and can capture complex Stock dynamics. We use an economic model with downward sloping demand for fish and Stock dependent costs. Then, we calculate the optimal harvest profile as a feedback control rule. We analyze effects of different level stochasticity. We observe that the stochastic solution is more conservative compared to deterministic solution apart from a very small Stock level, however, the effect from increased stochasticity is small at high Stock levels. We simulate the system forward in time with the optimal solution. In simulated paths some Stock Collapsed, while other recovered. The paths are easily identified and we group the paths and estimate the probability of Collapse for a given Stock level. The precision of the estimate only depends on the number of paths. We have also looked at the time required for Stock to reach stable level. The system needs more time to stabilize if the initial Stock level is small and with stochasticity. Finally, the stochastic Stock stabilizes on a level which is lower than the deterministic level. In this study, we demonstrate an approach to quantify stochasticity in fish Stock dynamics, derive the optimal stochastic harvest profile, and demonstrate a method to assess the risk of Collapse.
Colin Clark - One of the best experts on this subject based on the ideXlab platform.
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Marine Reserves: from Beverton and Holt to the Present
Reviews in Fish Biology and Fisheries, 1998Co-Authors: Sylvie Guénette, Tim Lauck, Colin ClarkAbstract:The idea of using marine reserves, where all fishing is banned is not new to fisheries management. It was first formally considered by Beverton and Holt but rejected in favour of approaches such as fleet and gear control. Since that analysis, many fisheries have Collapsed worldwide, illustrating the vulnerability of fishery resources and the ineffectiveness of these approaches. Empirical data and modelling suggest that marine reserves would generally increase yields, especially at the high fishing mortality that occurs in most fisheries. However, the most interesting feature of reserves is their ability to provide resilience to overexploitation, thereby reducing the risk of Stock Collapse. Benefits from reserves come from the increase in biomass and individual size within them, resulting in adult migration and/or larval dispersal that would replenish fishing grounds. The use of marine reserves in managing fisheries necessitates a thorough understanding of critical habitat requirements, fish movement, fish behaviour, the relations between subpopulations and the critical density effect for larval dispersal. When properly designed, and coupled with other management practices, reserves may provide a better insurance against uncertainties in Stock assessment, fishing control and management by protecting a part of the population from exploitation. This strategy can be used for both sedentary and migratory species.