Deterring Environmental Crime: Nautical Patrol and Illegal Fishing Practices

Abstract
Achilles heel of many environmental regulations is its enforcement. Fishing is no exception. A variety of regulations are designed to protect fish, a common property resource, from overexploitation, but detecting violations of these regulations is challenging, both at sea and in port. We present a novel approach to uncover a supposedly widespread and particularly harmful illegal fishing practice, the use of nets with illegally small mesh size. Our approach relies on readily available data on reported fish landings. We exploit the fact that the use of illegally small mesh size increases the proportion of small fish in the catch. Using quasi-random variation in nautical patrol as a source of variation in the incentive to comply, we show that in weeks without patrol the proportion of small fish in the landed catch is systematically larger than in weeks with patrol. Our results are in line with widespread use of illegally small mesh. The resulting catch and discard of juvenile fish is approximated to be more than forty times larger than the gain in the catch of marketable fish. This harm has thus far been largely ignored in estimates of the externalities from fishing. Joint paper with Stephen Kastoryano.