I mean, extinctions of giant fish, not giant extinctions of fish! This is about a paper that I read last year & put aside as a 'general interest' topic for when I was looking for something to write about.
The paper caught my eye because the title photo is of this amazing giant catfish (plus proud fisherman). It's a huge fish (they grow up to 3m long & can weigh up to 300kg) – and sadly, one which is becoming increasingly rare in its Mekong River habitat. In fact, many of the world's largest freshwater fish populations are declining, due to a combination of overfishing & degradation of their habitat through pollution and changing water use (eg damming waterways can block migration routes).
Why focus on the big ones? Stone quotes environmental scientist Thomas Lovejoy: Much like tigers on land, they are flagship species representing the wonders of life in rivers. Taking action to save these 'megafish' must entail conserving and restoring their habitat, so other fish species will benefit as well. (And it's easier to get people interested in the plight of large, exciting animals than the small, wriggly ones. Even more so when we're talking fish – people seem to be more interested when the animal is feathered or furry.) And there are social issues involved as well: the local fishing communities depend on selling the fish for their income, so how do you save the megafish (& their ecosystem) without destroying the community?
Unfortunately, for many of the fish discussed in Stone's article, scientists know very little about them. The fear is that they will become extinct even before researchers can identify what can be done to save them. Even if the species survive, sustained fishing may affect their evolution: if humans are constantly taking the largest animals, then this is placing strong selection pressure on the population: where smaller fish are surviving (being selected for), then it's their genes that will be passed on to the next generation.
R. Stone (2007) The last of the leviathans Science 316: 1684-1688
PS This item – like the last – was brought to you from St Pierre d'Albigny in southeastern France. Ah, the joys of modern technology!