ISSN:1064-1262    

DOI:10.1080/10641269309388533

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Hydroelectric development on the Columbia and Snake Rivers substantially impacted salmonid populations. The 1980 Pacific Northwest Electric Power Planning and Conservation Act mandated development of a program to mitigate these impacts. Hydroacoustics was one of the techniques that were applied to study the temporal and spatial characteristics of the downstream salmonid migration. Over 60 hydroacoustic studies were conducted at the various hydroelectric facilities on the Columbia and Snake Rivers during the 1980s. The primary objectives were measurement of run timing, vertical distribution, horizontal distribution, diel distribution, spill efficiency, and bypass efficiency. The techniques provided a cost‐effective, nonlethal, and accurate means to study passage rates, migration paths, and efficiencies of various operational and bypass mechanisms. In at least one case, the techniques were instrumental in the development of a successful bypass procedure. The development of hydroacoustic techniques for the Columbia and Snake Rivers contributed to successful applications of these techniques throughout the world, although more widespread application is hindered by the complexity and lack of understanding of the techniques.

ISSN:1064-1262    

DOI:10.1080/10641269309388534

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Fisheries of enclosed and semi‐enclosed seas provide the first basis for evaluating human impacts on marine ecosystems. These have become of serious concern before similar changes are detectable in oceanic systems, thus emphasizing their value as laboratories for comparative study of man‐induced changes. The paper discusses the relevance of the cline, oligo‐meso‐eu‐dys‐trophic to stressed marine systems, and focuses on impacts on fisheries of enhanced nutrient runoff, noting common features with marine systems subject to natural enrichment, but also with well‐studied freshwater systems. It is suggested that under nutrient enrichment and heavy fishing, both “top down”; and “bottom up”; trophic mechanisms act in synchrony to change the trophic chain, leading initially to increased fishery productivity of formerly oligotrophic systems, followed by more drastic and negative changes as nutrient input passes beyond a state that may be called mesotrophic.

ISSN:1064-1262    

DOI:10.1080/10641269309388535

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor