One of the most reliable ways of locating tuna stocks is by following dolphins. Once you find dolphins feeding on the fish, you set your nets around and catch them. Of course, this method will sometimes lead to you catching dolphins as well. In eighteen years of dolphin set tuna fishing in the United States, 18 dolphins were recorded as caught, along with 34 tonnes of sharks and rays and 295 tons of other fish. Such by-catch is virtually always discarded. In an equivalent period of dolphin safe fishing (where electronic Fish Aggregation Devices are used instead), no dolphins were caught, but 237 tonnes of sharks and rays were, along with 15,500 tonnes of other fish. Again, this was discarded.
Dolphin safe fishing is also disproportionately likely to catch immature tuna, which have not yet reached their full size and which have contributed very little to reproducing the species, since tuna generally take a long time to reach sexual maturity.
This only makes sense if you strongly privilege dolphins over other forms of marine life. Either because:
- You think dolphins themselves are bearers of rights
- People have much stronger preferences regarding dolphin treatment than that of other elements of marine ecosystems, and those preferences determine what is moral.
Admittedly, each of these is a viable moral position consistent with the ways in which we generally view what kinds of things can bear rights. That said, the trend in ecology is towards recognizing the importance of ecosystem integrity. From this perspective, setting nets around dolphin pods is probably the greenest way of catching tuna. This is especially true since it is possible to design nets that dolphins virtually always escape, but tuna do not.
Of course, now consumers know that to be eco-friendly, they are meant to buy the dolphin safe tuna. Confident in the belief that the problem has been dealt with, not enough people realize that we have probably made things worse.