摘要:

Hypotheses concerning the decline of Steller sea lions in the Gulf of Alaska (GOA) were evaluated based on comparison of data to three other ecosystems that had similar environmental and commercial fishery characteristics. We focus on examining the effects of commercial pinniped harvest, commercial fisheries, and environmental changes. Of the four pinniped species included in this study, only the Steller sea lion population has exhibited a sharp decline in population number. Comparative analysis indicated that the Gulf of Alaska pinniped population has not experienced any unique large-scale perturbations compared to the other ecosystems.Commercial pinniped harvest occurred in all four ecosystems. The history of harvest was shortest for GOA Steller sea lions and the numbers taken were lower than in the Barents Sea and Benguela Current ecosystems. Exploitation rates, though only calculated for years when both harvest numbers and total population size were available, also indicated that the Steller sea lions have experienced very little commercial harvest pressure compared to the other pinniped populations in the three other ecosystems. The age group of animals killed was comparable throughout all ecosystems.Large-scale variability in water temperature was common to all four ecosystems. Although the periodicity of the changes varied among ecosystems, they all appeared to be driven by low pressure systems. The variability of the oscillations in water temperature was lowest for the eastern Pacific ocean (i.e., the GOA and California Current ecosystems) and highest in the Benguela Current.Commercial fisheries played a major part in all four ecosystems. The main species in pinniped diets were often the target of commercial fishing activity leading to potential conflicts between the 2 types of predators (i.e., pinnipeds and commercial fisheries). Exploitation rates in the GOA were comparable to or less than rates in the other ecosystems while the rates were highest in the Barents Sea. Statistical analysis showed that GOA pollock exploitation rates were significantly different from the rates of most other species. Healthy pinniped populations were present in all the ecosystems in this study except for the GOA despite the presence of much commercial fishing activity. This suggests the need for more detailed analysis of the possible role of commercial fisheries in the GOA ecosystem and the management actions taken to alleviate its effects.

ISSN:1064-1262    

DOI:10.1080/10641260091129189

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Sedimentation and turbidity are significant contributors to declines in populations of North American aquatic organisms. Impacts to lotic fauna may be expressed through pervasive alterations in local food chains beginning at the primary trophic level. Decreases in primary production are associated with increases in sedimentation and turbidity and produce negative cascading effects through depleted food availability to zooplankton, insects, freshwater mollusks, and fish. Direct effects at each trophic level are mortality, reduced physiological function, and avoidance; however, decreases in available food at trophic levels also result in depressed rates of growth, reproduction, and recruitment. Impacts of turbidity to aquatic organisms often seem inconsistent among watersheds and experiments, but this apparent difference is actually due to the lack of correlation between suspended sediment concentrations (mg/L) and units of measure (Nephelometric Turbidity Units, NTU). The use of NTU as a surrogate measurement of suspended sediment to predict biotic effects within watersheds is dubious. Similar NTU measurements from different watersheds may be correlated with different concentrations of suspended sediment. For monitoring the effects of turbidity within local watersheds, we recommend that the correlation between suspended sediment and NTUs be examined over a range of discharge recordings, and that this be used as a baseline to examine local effects. We recommend that riparian buffer strips and livestock fencing be used to reduce sediment input to streams.

ISSN:1064-1262    

DOI:10.1080/10641260091129198

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

There have been many efforts to create a conceptual framework for understanding and defining sustainable aquaculture. A recent consensus or stakeholder view (Caffey et al., 1998) approached sustainability from three perspectives: environmental, economic, and sociological. Often, stakeholder views are snapshot or present oriented. The multiple variables affecting sustainability and viability are considered from a here-and-now perspective rather than considering the effects that significant change in one or several variables might cause. Aquatic nitrogen loads generated from the sewage effluent of a growing, global human population (15 billion vs. 6 billion people) may prevent the legal discharge of any aquacultural effluents. Much of the intensive aquaculture industry has a highly centralized structure with respect to production and distribution. This centralized development has flourished around energy-rich — at times extravagant — cultures and economies. How will increased costs or shortages of electricity, gasoline, and diesel fuel affect the sustainability or survival of the current production system? Does a large, centralized industry provide more jobs and profit or a better quality of life (per capita) than widely dispersed, small-scale operations producing at local or county levels?Nutrient recycling (converting nitrogen back to protein) through different polyculture systems could be more practical and efficient than controlling or treating the effluents associated with traditional, intensive monoculture practices. Phytoplankton and zooplankton occupy sizable respiratory (oxygen consumption) niches in the production pond environment — and have no market value. Careful selection of suitable filter feeding fish and mollusks for polyculture could open up these niches for the production of species with greater economic value. It might be more desirable to culture channel catfish with paddlefish and some species of freshwater mussel than to face bankruptcy because it has become illegal to discharge effluents from production ponds used for intensive monoculture. Ultimately, sustainability may be the aquaculture industry's ability to adapt on a planet with an ever-increasing human population that continues to consume its limited supply of nonrenewable resources at an alarming rate.

ISSN:1064-1262    

DOI:10.1080/10641260091129206

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor