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As the fisheries of the continental shelves have become fully exploited (6), the search for commercially valuable species has moved off the continental shelf and onto the upper slope and offshore seamounts, resulting in depletion of deep-water stocks and also with consequences for benthic habitats (7). Deep-sea trawl gear is large and heavy. The paired otter doors, which are metal plates pulled at an angle to the direction of movement of the ship and therefore act to spread the net, can weigh as much as 5 tons each. The bottom leading edge of the net, called the footrope, is armed with stainless steel bobbins or rollers and often rubber disks that are 30 cm or so in diameter, thus allowing the net to traverse rough bottom with minimal damage to the net. Large sediment plumes are generated by the turbulence created as the doors, ropes, and net are pulled across sandy or muddy bottoms at speeds up to 4 kn, and grooves are made in the sediment that can last for a very long time (8) (Fig. 1A). Puig et al. (1) demonstrated that bottom muds resuspended by trawling activity along the upper continental slope could be transported over long distances, often going down canyons to deeper waters, simultaneously drastically reducing the bottom topography and habitat heterogeneity in the area where trawling was frequent.
Search results for steel beasts
Military technology reached a turning point in the First World War, which saw widespread use of machine guns, poison gas, and indirect artillery fire. Massed formations and desperate charges were decisively outmatched by the new weaponry, with bloody results. World War I was the first war in which American soldiers were issued steel combat helmets, a precursor to the elaborate body armor that exists today. (National Guard Heritage Collection)
The mass production of tanks during the Second World War was a death knell for the linear fighting formations that had for so long constrained battlefield tactics. The steel beasts could break through a firing line with ease, but dispersed and hidden infantrymen could destroy an unwary tank with a variety of armor-piercing weaponry. (National Guard Heritage Collection) 041b061a72