Some have argued that open-access fisheries will always be subject to more exploitation than are private fisheries. The reasoning is that each fisherman will be more likely to over fish open-access fisheries because he alone reaps the benefits, while the costs of mitigating measures to prevent the collapse of over-exploited fisheries is borne by all. Despite this, one study of 250 common-access fisheries and 103 private fisheries showed that the open-access fisheries were less exploited than the private ones.

Which of the following, if true and known by the fishermen, is the best explanation tor the results of the study?