Globally, we do not know if fishing adheres fully to the law. Fish caught on accident or bycatch and fish thrown over board called discards have a cascading effect within fisheries, and are also a source of controversy in fisheries policy, law and enforcement. Measuring how effective enforcement measures are for reducing bycatch and discards is pivotal to understanding fisheries compliance with the law, and for developing strategies to reduce resource waste in fishery systems. In Greenland, more than 75% of all large-scale fishing is conducted without direct monitoring of a fishery observer aboard. While this sector creates about 75% of the value in Greenland ($52 million in 2017), little is known about the resource wastes associated with fishing, be it monitored or not. Using digital logbook records from all of Greenlands fisheries, we use matching techniques to process observations of trips from the last five years (2012-2017), with and without observers (N=5144). For each fishery, we present the likelihood of fishery observers driving bycatch and discards, as well as the effects of interaction terms such as haul time, vessel nation, gear type, season, and area. We also calculate the costs of the resource wastes that accue under the two enforcement scenarios of an observer aboard, or under standard, nonphysical control procedures. Our results clarify the costs and benefits of fishery observer programs designed for enforcement. We anticipate that that our methods will be of value to work on causal inference in the environmental social sciences and ongoing dialogue concerning the role of fishery observers in the montoring, control, and surveillance of fishing.