It gets entangled in the illegal gillnets targeting totoaba, which is also an endangered species. In the Western Mediterranean Sea, the illegal Italian swordfish driftnet fishing very seriously threatens the striped local dolphin population. An even more dramatic effect of overfishing arises from the depletion of prey species populations. North Atlantic seals, Northwest Atlantic whales and UK seabirds are known to have suffered starvation and population collapses when the species they relied upon have been depleted or seriously reduced. This is very much the case with some of the small fish species which are at the lowest level of the marine trophic web, such as sand-eels, anchovies, pilchards, capelin, and krill.
Fisheries also have an impact on biodiversity through the degradation of marine habitats.
Dynamite-fishing is widespread, and when it is practised in coral reefs, one of the most diverse ecosystems in the world, it not only kills fish but also damages and degrades the reef. Another example is trawling in shallow waters, a common practice in many areas of the world. Shallow waters host the most complex and diverse marine ecosystems thanks to the availability of both nutrients and sunlight. In every continental water system, populations have evolved in relative isolation, in a permanent process of adaptation to their environment. This has lead to the selection of particular combinations of genes which result in a maximum adaptation for a given environment.