The economic case for government subsidies can be made in one of two ways. The first is the argument based on externalities: the idea being that one person’s behaviour creates benefits for others, but that those others do not compensate the actor. An example might be a landowner who refrains from cutting down trees uphill from rivers. All river users benefit from the flood control and lack of silt. In this case, it might make sense for the government to pay the landowner to save the trees – in providing the subsidy, the government encourages a more socially optimal behaviour. This justification doesn’t work for fisheries. Fisheries are a common property resource and, as such, tend towards over-exploitation. Having fishers catch more does not provide anyone else with benefits; indeed, it harms the ability of everyone else to use marine resources. Subsidizing fishing pushes fishers to continue catching fish even beyond the point where it would normally be unprofitable, leading to further depletion.
The second argument for subsidies is the ‘infant industries’ argument. The idea here is that it can take a while for a new business to reach the level of existing businesses in the field. A brand new textile industry in an African state may not initially be able to produce goods at a cost and level of quality competitive with existing industries in Asia. In such cases, you can justify a temporary program of subsidy, intended to get the industry running. Once again, this doesn’t apply to fisheries. If anything, there is too much fishing capacity in the states that subsidize heavily (North America, Europe, and Japan). Excess fishing capacity is being exported into developing states, depleting the resources there.
The one form of subsidy that can be justified in relation to the fishing industry is subsidized training to get out of it. We can recognize that fishers are having an increasingly difficult time making a living, while also recognizing that subsidizing their fuel or equipment will just batter fish stocks further. The solution is to help people to transition into other industries where they can sustain themselves without depleting pools of resources common to everyone. It is always hard for politicians to say that an industry should be smaller, or should not exist at all, but, in the case of fisheries, that is probably the only position that makes economic and ecological sense.