Download or read book Ecological Interactions Among Important Groundfishes in the Gulf of Alaska written by Cheryl L. Barnes and published by . This book was released on 2019 with total page 386 pages. Available in PDF, EPUB and Kindle. Book excerpt: Complex ecological interactions such as predation and competition play an important role in shaping the structure and function of marine communities. In fact, these processes can have greater impacts than those related to fishing. We assessed ecological interactions among economically important fishes in the Gulf of Alaska – a large marine ecosystem that has recently undergone considerable shifts in community composition. Specifically, we developed an index of predation for Walleye Pollock (Gadus chalcogrammus) to examine spatiotemporal changes in consumption, quantify portfolio effects, and better understand diversity-stability relationships within the demersal food web. We also evaluated the potential for competition between two important pollock predators, Arrowtooth Flounder (Atheresthes stomias) and Pacific Halibut (Hippoglossus stenolepis). We found highly variable predation intensity on Gulf of Alaska pollock. The combination of a single dominant predator and synchronous consumption dynamics indicated strong top-down control in the region. Spatial heterogeneity, however, may offset trophic instability at the basin scale. Assessments of resource partitioning provided little indication for competition between Arrowtooth Flounder and Pacific Halibut of similar lengths. Morphological differences between the two flatfish predators prompted an exploration into whether our conclusions about resource partitioning were dependent upon the size metric used. From this study, we found a relatively early onset of piscivory for Arrowtooth Flounder. Relationships between predator size and prey size also suggested gape limitation among Pacific Halibut sampled. Trophic niche separation was more pronounced for fishes with larger gapes, indicating greater potential for competition among smaller Arrowtooth Flounder and Pacific Halibut in Southeast Alaska. Reexamining basin-scale relationships between spatial and dietary overlap according to gape size would further elucidate the effects an increasing Arrowtooth Flounder population has had on changes in Pacific Halibut size-at-age. Results from this dissertation improve our understanding about the impacts of complex ecological interactions on population and community dynamics, and how those interactions may change in time, space, and under different environmental conditions.

Download or read book The Factors Affecting the Diets of Groundfish in the Gulf of Alaska written by Kevin A. Thompson and published by . This book was released on 2015 with total page 95 pages. Available in PDF, EPUB and Kindle. Book excerpt: Marine systems undergo changes in community composition over time as a result of a variety of environmental and anthropogenic factors. Understanding these community changes and the factors that drive them is critical for ecosystem management of marine resources. The Gulf of Alaska (GOA) is a large marine ecosystem that includes a variety of species that support large scale fisheries. This is also a system in which large scale community shifts, or regime shifts, have occurred due to the Pacific Decadal Oscillation (PDO) and fishing pressure. Given the economic and conservation importance of this marine system, the GOA has been modeled using a variety of multispecies, or ecosystem, models. While this work has been critical in understanding the ecosystem dynamics of the GOA and helped generate management recommendations for commercial species, these models often make assumptions regarding trophic-dynamics, particularly that predator-prey relationships follow a standard functional response and do not change through time in response to environmental variables. However, empirical evidence suggests that a predator's diet can be influenced by a variety of factors, abiotic and biotic, at large and small spatial scales. Our overall objective was to investigate the potential impact environmental variables may have in structuring this ecosystem by using statistical analyses of diets and an ecosystem modeling framework. We focused on three commercially and ecologically important groundfish predators: Pacific Cod (Gadus macrocephalus), Pacific Halibut (Hippoglossus stenolepis), and Sablefish (Anoplopoma fimbria). We also focused on a key prey species, Walleye Pollock (Gadus chalcogrammus), and used environmental data collected during trawl surveys and PDO data generated for the entire North Pacific region. The first study completed was focused solely on the consumption of Walleye Pollock, a critical fishery species and ecosystem link. We used data from trawl surveys to determine the potential influence of local environmental variables on the predation rate of Walleye Pollock in the system by these groundfish. Using an information-theoretic approach, we found that predator length was positively related to Walleye Pollock presence and proportion of total diet weight in all predators. Increased temperatures positively affected consumption of Walleye Pollock by Pacific Halibut, but not the other predators. We found evidence for a number of inter-predator effects of co-occurring predators, both positive (facultative) and negative (competitive). Observed prey density was not statistically significant with respect to consumption for these predators, suggesting that trawls sample the environment differently than Walleye Pollock predators or species interactions are more complex than those used in previous multispecies models. In our second study, we considered the entire diet of these predators, rather than one key prey. Furthermore, because PDO had been described as leading to community changes in the system previously, we hypothesized that it could also be driving shifts in diets in the three groundfish predators we studied. We used a multivariate statistical approach to compare the diets of these predators by PDO state (warm or cold years) and also included local environmental covariates. Overall, we found that diets observed in PDO cold years were significantly different than diets in fish in warm years. In general, predators were found to be consuming more Walleye Pollock and euphausiids in warm years, and more benthic invertebrates and other forage fish in cold years. Local environmental covariates contributed to the diets observed in these predators, however no general pattern was observed. Our results also show the benefit of using diet data from large scale monitoring efforts as indicators of community shifts in a large marine ecosystem through time. Ultimately, we used our statistical analyses regarding diet and PDO state to drive a modeling exercise using alternate representations of the diets of the predators in the GOA. We investigated the potential impact of shifting diets in groundfish in an ecosystem-modeling framework, using Ecopath trophic-mass balance models. We changed the diets of key groundfish predators in the model based on our previous results for three alternative model parametrizations; 1) average conditions over the time period, 2) cold PDO state, and 3) warm PDO state. We noted a number of differences in model estimated ecosystem indices. Biomass accumulation estimates indicated that some ecologically and commercially important species groups would be expected to greatly diverge in population size if models were based on data from warm vs. cold PDO years compared to the averaged climatic state. In general, predator overlap was at its lowest in the cold year model, as predators had more diverse diets and therefore predation was more diffuse in the system in general. These results indicate the potential importance of environmental context when collecting diet data to be used in ecosystem models designed to provide fishery management recommendations. As ecosystem models are used more commonly, taking the time to investigate the factors that structure diets and how predation changes due to environment can yield more representative, and potentially more accurate biomass projections and recommendations for the GOA and likely many other managed marine ecosystems.

Download or read book Long term Ecological Change in the Northern Gulf of Alaska written by R.B. Spies and published by Elsevier. This book was released on 2006-12-12 with total page 609 pages. Available in PDF, EPUB and Kindle. Book excerpt: This comprehensive text is a major synthesis on ecological change in the Gulf of Alaska. It encompasses the structural and annual changes, forces of change, long-ecological changes in the atmosphere and ocean, plankton, fish, birds and mammals, and the effects of the 1989 Exxon Valdez Oil Spill. With 5 major sections, Long-term Ecological Change in the Northern Gulf of Alaska first describes the physical features, the atmosphere and physical oceanography, the annual production cycle, the forage base for higher animals and trophic transfer, and the adaptations for survival in this changing environment for 9 portal species. Then, the major forces of change are introduced: climate, geophysics, fisheries and harvesting, species interactions, disease and contaminants. Next, the long-term records of change in physical factors and biological populations are presented, as well as the potential reasons for the biological changes. Following is the history of the Exxon Valdez oil spill and its long-term effects. And, finally, the emergent properties of the ecosystem are discussed and an attempt is made to weigh the importance of the major forcing factors in terms of their temporal and spatial scales of influence. * Examines important data on long-term change in the ecosystem and the forcing factors that are responsible for it * Provides an account of the 1989 Exxon Valdez oil spill with emphasis on the long-term effects * Describes the effects of climate change, geophysical change, species interactions, harvesting, disease, the 1989 oil spill, and marine contaminants on key populations of marine organisms

Download or read book Fishery Management Plan and Environmental Impact Statement for the Gulf of Alaska Groundfish Fishery During 1978 written by North Pacific Fishery Management Council and published by . This book was released on 1977 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Programmatic Supplemental EIS for Alaska Groundfish Fisheries Implemented Under the Authority of the Fishery Management Plans for the Groundfish Fishery of the Gulf of Alaska and the Groundfish of the Bering Sea and Aleutian Islands Area written by and published by . This book was released on 2004 with total page 810 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Food Habits of the Commerically sic Important Groundfishes in the Gulf of Alaska in 1990 1993 and 1996 written by Mei-Sun Yang and published by . This book was released on 2000 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Groundfish Total Allowable Catch Specifications and Prohibited Species Catch Management Plans for the Groundfish Fishery of the Bering Sea and Aleutian Islands Area and Groundfish of the Gulf of Alaska written by and published by . This book was released on 1998 with total page 846 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Alaska Groundfish Harvest Specifications written by and published by . This book was released on 2007 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Draft EIS provides decision-makers and the public with an evaluation of the environmental, social, and economic effects of alternative harvest strategies for the federally managed groundfish fisheries in the Gulf of Alaska (GOA) and the Bering Sea and Aleutian Islands (BSAI). The EIS examines alternative harvest strategies that comply with Federal regulations, the Fishery Management Plans for the GOA and BSAI groundfish fisheries, and the Magnuson-Stevens Act. The harvest strategies are applied to the best available scientific information to derive the total allowable catch for the groundfish fisheries.

Download or read book Essential Fish Habitat Designation and Minimization of Adverse Impacts Pacific Coast Groundfish Fishery Management Plan written by and published by . This book was released on 2005 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gulf of Alaska Groundfish Fisheries Management Plan FMP 1978 written by and published by . This book was released on 1977 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Programmatic Supplemental EIS for Alaska Groundfish Fisheries Implemented Under the Authority of the Fishery Management Plans for the Groundfish Fishery of the Gulf of Alaska and the Groundfish of the Bering Sea and Aleutian Islands Area written by and published by . This book was released on 2004 with total page 868 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Food habits of the commercially important groundfishes in the Gulf of Alaska in 1990 written by Mei-Sun Yang and published by . This book was released on 1993 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Our Living Oceans written by and published by . This book was released on 1991 with total page 486 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Amendment 16 3 to the Pacific Coast Groundfish Fishery Management Plan Rebuilding Plans for Bocaccio Cowcod Widow Rockfish and Yelloweye Rockfish written by and published by . This book was released on 2004 with total page 330 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Regulatory Impact initial Flexibility Analysis of Proposed Inshore offshore Allocation Alternatives Amendment 18 23 to Groundfish Bering Sea and Aleutian Islands Fisheries Management Plan FMP and Gulf of Alaska Groundfish Fisheries Management Plan FMP written by and published by . This book was released on 1992 with total page 852 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book American Fisheries Act Amendments 61 61 13 8 written by and published by . This book was released on 2002 with total page 844 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fishery Management Plan for the Gulf of Alaska Groundfish Fishery written by North Pacific Fishery Management Council and published by . This book was released on 1979 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt: "As directed by the Fishery Conservation and Management Act of 1976 (P.L. 95-265) the North Pacific Fishery Management Council is preparing fishery management plans for those fisheries within its area of jurisdiction. This document was the first of the plans to be completed by the Council since its formation in October, 1976. The Fishery Management Plan for the Gulf of Alaska Groundfish Fishery was developed by a multi-agency team composed of members from the National Marine Fisheries Service, the Alaska Department of Fish and Game, the International Pacific Halibut Commission and the University of Washington. It was approved by the North Pacific Fishery Management Council on September 24, 1977, for submission to the Secretary of Commerce. Regulations to implement this plan were published on the same date. It was approved by the Secretary of Commerce and published in the Federal Register on April 21, 1978. The Plan has been amended seven times, beginning December 1, 1978 (Amendment 1 implemented) and most recently, November 1, 1979 (Amendment 7 implemented). An explanation of these amendments is attached."-- from page 1.