萎缩了的鱼群

一千年前,生活在我的家乡约克市的挪威人吃的鳕鱼重达八公斤。我们有幸得知这些是因为考古学家一向对中世纪的废物堆保持着浓厚兴趣。但今天,能得见超过两公斤的鳕鱼就已经算是幸运了。人类做了什么,使鱼类发生如此变化?这一点是否关系重大呢?

渔业政策旨在保护幼苗得以生长。原因不证自明:捕捞幼鱼会导致重量上大幅减产;而且鱼群也将因此失去繁殖机会,招致鱼类总储备量下降。例如, 欧盟共同渔业政策就是"通过调节海上捕捞数量、允许鱼苗繁殖和保证此类政策被切实执行来保护渔源"。

然而,就目前情况看,我们已经破坏了鱼类储备。存活下来的大鱼、成鱼寥寥无几。北海的鳕鱼就是很好的例证。假设选出一万条年龄一岁的鱼类个体作为研究对象,若只考虑自然死亡,大约有一千条能存活八年。但捕捞造成的死亡把这个数字降到了一百条左右。而由于过去二十年里的过度捕捞,该数字已经降到了大约三条。

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