Littérature scientifique sur le sujet « Disturbo Uso Sost »

<em>Abstract.</em> —Seabed disturbance by mobile bottom-fishing gear has emerged as a major concern related to the conservation of essential fish habitat. Unquestionably, dredges and trawls disturb the seabed. However, the seabed is also disturbed by natural physical and biological processes. The biological communities that utilize a particular habitat have adapted to that environment through natural selection, and, therefore, the impact of mobile fishing gear on the habitat structure and biological community must be scaled against the magnitude and frequency of seabed disturbance due to natural causes. Fishers operating in the mouth of Narragansett Bay, Rhode Island use trawls to harvest lobsters, squid, and finfish and dredges to harvest mussels. These mobile fishing gears impact rock, sand, and mud substrates. Side-scan sonar data from 1995 with 200% coverage were available from the National Oceanic and Atmospheric Administration for the mouth of Narragansett Bay. Analysis of these data indicates that evidence of bottom scarring by the fishing gear is restricted to deeper waters with a seabed composition of soft cohesive sediments, despite the observation that fishing activity is ubiquitous throughout the bay mouth. A quantitative model has been developed to compare the magnitude and frequency of natural seabed disturbance to mobile fishing gear disturbance. Wave and tidal currents at the seabed are coupled with sediment characteristics to estimate the degree of seabed disturbance. Field experiments designed to compare the longevity of bottom scars indicate that scars in shoal waters and sand sediments are short-lived, as compared to scars in deep water and mud sediments, which are long-lasting. Finally, the model results are compared to the recovery time of sediments disturbed by the interaction of the fishing gear with the seabed. The impact of mobile fishing gear on the seabed must be evaluated in light of the degree of seabed disturbance due to natural phenomena. The application of this model on a larger scale to continental shelf waters and seabed sediment environments will allow for the identification of problematic areas relative to the degradation of essential fish habitat by mobile fishing gear.

<em>Abstract.</em> —Seabed disturbance by mobile bottom-fishing gear has emerged as a major concern related to the conservation of essential fish habitat. Unquestionably, dredges and trawls disturb the seabed. However, the seabed is also disturbed by natural physical and biological processes. The biological communities that utilize a particular habitat have adapted to that environment through natural selection, and, therefore, the impact of mobile fishing gear on the habitat structure and biological community must be scaled against the magnitude and frequency of seabed disturbance due to natural causes. Fishers operating in the mouth of Narragansett Bay, Rhode Island use trawls to harvest lobsters, squid, and finfish and dredges to harvest mussels. These mobile fishing gears impact rock, sand, and mud substrates. Side-scan sonar data from 1995 with 200% coverage were available from the National Oceanic and Atmospheric Administration for the mouth of Narragansett Bay. Analysis of these data indicates that evidence of bottom scarring by the fishing gear is restricted to deeper waters with a seabed composition of soft cohesive sediments, despite the observation that fishing activity is ubiquitous throughout the bay mouth. A quantitative model has been developed to compare the magnitude and frequency of natural seabed disturbance to mobile fishing gear disturbance. Wave and tidal currents at the seabed are coupled with sediment characteristics to estimate the degree of seabed disturbance. Field experiments designed to compare the longevity of bottom scars indicate that scars in shoal waters and sand sediments are short-lived, as compared to scars in deep water and mud sediments, which are long-lasting. Finally, the model results are compared to the recovery time of sediments disturbed by the interaction of the fishing gear with the seabed. The impact of mobile fishing gear on the seabed must be evaluated in light of the degree of seabed disturbance due to natural phenomena. The application of this model on a larger scale to continental shelf waters and seabed sediment environments will allow for the identification of problematic areas relative to the degradation of essential fish habitat by mobile fishing gear.

The practice of procedural sedation involves the use of medications that alter upper airway function and patency because of myoneural suppression of anatomic airway elements. It is the specific responsibility of the sedationist to ensure upper airway patency during conditions induced by pharmaceuticals in which the airway is almost certain to be threatened, if not totally obstructed. Soft tissue collapse during inspiration is modeled by the Starling resistor. Airway protective reflexes may be profoundly disturbed during deep sedation. The sedationist’s knowledge of the anatomy and physiology of the upper airway and proficiency in clinical application of airway supportive principles are essential.

Given the discussion above regarding natural changes in the marine benthos, we should now consider the human-mediated (anthropogenic) changes and the response of benthic systems to human impacts. From the 1960s to the 1980s the general opinion seemed to be that pollution (considered in the next chapter) was the most important marine problem, but we now realize that habitat change and habitat loss are of greater concern: see, for example, the Quality Status Report 2000 (OSPAR 2000). One of the greatest effects on the integrity of the seabed and hence its biota is now known to be caused by bed trawling. This has now generated an enormous literature, and the reader is directed to Daans and Eleftheriou (2000) and Hollingworth (2000) for more details. We can take this information and summarize the overall ecosystem effects of fisheries in detailed flow diagrams (referred to as ´horrendograms´!) to show the interlinked and complex nature of the impact—the effects trawling are included here, but see also those in McLusky and Elliott (2004) (e.g. Fig. 8.1). Historically, the effects of trawling on benthos caused concern as early as 1376 when a petition was made to the English parliament by fishermen concerned over the damage done to the seabed and fisheries by bottom trawling (De Groot 1984). This was despite the gear used by sailing vessels in those days being relatively light and towed at slow speeds and in shallow water only. When steam trawlers were developed in the early 1900s, everything changed. The weight and size of trawls increased and use of tickler chains (mounted on the bottom rope to disturb bottom-living fish upwards and into the trawl net) were of great concern, although studies done in the 1970s to allay the fears of fishermen did not find long-term effects on macrobenthos (Jones 1992). At the end of World War II the otter trawl was developed and its use became widespread. This and the beam trawl (see Fig. 8.4) were (and still are) the types of gear most widely used to fish the seabed.

The purpose of this chapter is to consolidate. No new ideas are introduced; instead we try to sort the main thread from the side issues, and the parts that are reasonably clear and firm from the parts that are still fuzzy. The core of the chapter is a set of seventeen statements, seventeen vertebrae that form the backbone of the book, but there are also a preface and a postscript. The preface provides the setting for the seventeen-part core and the postscript takes up the question of where to go next. The purpose of the book was given at the start of Chapter 1. Even at that early point, a stressed cylinder was used as an example. The purpose is to make headway with the question: if a state of chemical equilibrium exists under hydrostatic stress and is disturbed by making the stress nonhydrostatic, what processes begin to run, and what quantitative relations should we expect to be followed? Before the seventeen-part "answer" it is to be noted that there are two alternative ways of dividing the subject matter into two parts. The division scheme is displayed in Figure 17.1a and separates eight types of change. (A somewhat similar diagram on page 111, distinguished eight circumstances in which change might be observed—a different system of divisions that is of no use here.) Of the eight boxes set up, four have been discussed, as shown in Figure 17.1b. The two ways of dividing this four-box group are by a horizontal cut or by a vertical cut that separates stars from superscript a’s. (A vertical cut separating the N-box from the rest is of no help; it would be contrary to our theme.) The horizontal cut separates stress-driven effects below from composition-driven effects above. It is in fact the traditional division between mechanics and chemistry; enormous amounts of science fall clearly above the cut or clearly below it and cause no confusion at all. This cut was used as a guide in the early chapters, especially in the flow diagram or organization chart, Figure 8.1. By contrast, the second cut appeared as late as Chapter 15, but deserves emphasis; it is at least as instructive and helpful as the first, and perhaps more helpful.