贝类心愿

渔业与环境--贝类心愿

怎样减小捕捞作业对海底的破坏

生活在海底的生物味道鲜美。然而,打捞这些珍稀物种,通常会破坏深海生物的栖息环境。目前研究者开发了一种更为温和的捕鱼方式。

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。

颇让人担忧的是,海绵,海藻和百年珊瑚都遭到了破坏。认真说来,这些固着动物不仅仅是生态系统的部分,一定意义上,他是森林一样的提供居住环境的生态系统,以植物生态系统的方式存在,而不是动物。事实上拖网捕鱼就像是彻底砍伐树木,从实用角度讲,这种栖息环境的破坏促使世界范围的鱼群缩小。

可喜的是,有了这样一个事情。针对扇贝捕捞,麻省理工的Cliff Goudey有了对策。他与研究小组设计的捞网,不用接触海底就可以捞取到扇贝。

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。

在实验室水池和马萨阻塞海面上进行对比实验评估后,最近Goudey博士被邀情到英国威尔士大学做新发明和传统捞网的对比实验。在英国的曼恩岛海域,新旧装置都是在拖捞船尾被放进水中,然后牵引捕捞。两类装置捕捞到的扇贝数量相同。但新捞网破坏的捕获物少于传统捞网。

对捞网装置的进一步测试是投入商业使用的监管测试。一丹麦渔业设备公司Visserijcooperatie Urk,对新装置感兴趣,想用于捕捞另一种海底栖息生物,比目鱼鳎。捕捉贝类时珊瑚安全的关注,只是一个小小的起步,下面还要关注对海豚无害的金枪鱼捕捞技术吧。

英文原版地址

Fishing and the environment-Shellfish desires

Aug 7th 2007
From Economist.com

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.

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