拖网捕鱼是广泛采用的捕鱼方式。但在海底，拖网捕鱼是很残酷的。海底捕捞时，绑有巨大锯齿状横杆的捕 捞装置，刮过海床。后面的拖网扫过时会将捕捞目标在内的海底生物尽收网内。可惜，拖网还带上来很多生活在深海区海床表面或下面的其他生物，渔业术语叫做一 网打尽。结果很多其他鱼类，甲壳类，软体动物无意中被捕捞上来。
这种捞网用几个半球状的铲子代替了锯齿横杆。拖拽时，半球铲子向下搅动水，形成一股股较温和的水流使 扇贝慢慢离开原来的静修地。而这种不特别强大的水流又不至于破坏深海内的长期房客。同时，如果半球铲子遇到任何坚实的固体，会旋转起来而不至于撞坏海底岩 石等隆起物。捕鱼者看来，最好的一点是Goudey博士的这种装置比传统的拖拽方法更省油。因为在不平的海床表面拖拽比用捞网搅水流要费劲多了。
Fishing and the environment－Shellfish desires
Aug 7th 2007
How to make trawling for fish less harmful to the seabed
TASTY species live at the bottom of the sea. Plucking these morsels from their habitat, however, is often a violent affair that destroys other denizens of the deep. Now researchers have developed a more benign way to fish.
Trawling is the most widespread form of fishing. But bottom trawling is brutal. It uses an enormous, toothed bar mounted on a device called a dredge to scrape the seabed. Dredging throws the intended catch up into a cloud that is captured by a net trailing behind. Unfortunately, the cloud contains a lot of other stuff. Anything at or just below the surface of the seabed-the benthic zone, in fishery parlance-gets dragged up. The result is that a lot of other types of fish, crustaceans and molluscs are caught unintentionally.
More worryingly, sponges, seaweeds and centuries-old coral are destroyed. This is serious because such sessile creatures are not merely part of the ecosystem. In a sense, they are the ecosystem-in the way that it is plants rather than animals that define a forest. Indeed, trawling has been compared to clear-cutting trees. Moreover, from a practical point of view, this destruction of habitat contributes to the dwindling of fish stocks worldwide.
However, in one case-scallop trawling-Cliff Goudey of the Massachusetts Institute of Technology reckons he has a solution. He and his team have designed a dredge that can dislodge scallops without touching the seafloor.
The dredge has several hemispheric scoops in place of the toothed bar. As it is pulled along, the scoops direct water downward. That creates a series of gentle jets that can shuffle the scallops from their resting places-but the streams of water are not powerful enough to damage the benthic zone’s long-term tenants. Also, the scoops swivel out of the way if they encounter anything solid, so the dredge does not destroy such protuberances. Best of all, from the fisherman’s point of view, it takes less effort to float a dredge on water jets than to drag it across the uneven surface of the seabed. That makes Dr Goudey’s device a more fuel-efficient way to fish than the traditional method.
Having assessed a prototype both in a laboratory tank and in the sea off the coast of Massachusetts, Dr Goudey was recently invited by the University of Wales to test his invention against a traditional dredge. New and old were dropped from the stern of a trawler and towed across the seabed off the Isle of Man. They each caught the same number of scallops. The new dredge, though, damaged the catch less than the traditional one.
Further tests will take the dredge over the regulatory hurdles toward commercial use. Visserijcooperatie Urk, a Dutch fisheries-equipment firm, has already expressed an interest in using the new device to catch sole, another bottom-dwelling species. A humble start-but it may yet be worth keeping an eye out for coral-safe scallops next to the dolphin-friendly tuna.