In many developing countries, food and income associated with fishing are important to the poor. When fishing is subsidized, those people suffer the most. Who benefits? Well, of course people doing the fishing benefit, but also people who consume a lot of fish benefit in the short run from lower prices (though we pay the difference as taxes). However, those people can expect to pay higher prices later as fish become scarce more quickly.
It's cases like agricultural and fishing subsidies that put environmentalists and libertarians in the same camp, which is relatively rare. Too bad their combined energies are not enough to persuade politicians to cut back on the subsidies!