Effectiveness of the law
A rule of law is considerd as being effective when it is applied and observed by those for whom it is intended. This gives rise to many problems in international law, especially as concerns the law of the sea. Two levels of effectiveness can be distingushed, though they are eminently complementary. For a rule of law to be effective, the States concerned must have entered into a commitment to observe it, and also to have take then steps necessary to ensure its observance.
Firstly, a rule of international law is only imposed on a person, a vessel or in the context of an activity if the State to which they are attached has agreed to be bound by it following a customary or conventional process (cf. Conditions for a State's Commitment). In this case, the rule is opposable to the State concerned, which is responsible for ensuring that the rule is observed by its nationals and within its territory. In other cases, ie. for Other States, the rule of law exists but is not applicable to them. Depending on the number of States which are concerned by application of the rule, and which have agreed to be bound by it, it can be more or less effective. An international convention adopted by a modest number of States, or by States barely concerned by the activities it targets, will be seen as being only slightly effective.
Secondly, a State's commitment to the rule does not suffice to guarantee its effectiveness. In fact, a State may agree to be bound by a rule of international law, but then fail to ensure that it is observed by those under its authority, whether vessels flying its flag, its nationals or those who are present in areas, especially maritime, which are under its jurisdiction. In the law of the sea, such failure to apply the law may be explained by material difficulties in carrying out controls (for example, due to the distance covered by ships from their flag State, particularly when pursuing their activities on the high sea; due to the vast extent of the areas over which States exercise their authority, especially in an EEZ; or because of economic, political or social difficulties that certain States may be experiencing).
Such difficulties may be circumvented by the adoption of cooperation agreements among States allowing each party to carry out controls on the other parties' vessels. These agreements thus make it possible to go beyond the principle of the flag State's exclusive authority on the high sea, or the principle of the coastal State's exclusive rights to exploitation and conservation of natural resources in its EEZ. Such a system makes it possible to compensate for the lack of means or the distance of certain States from the activity zone in which the rule must be observed.
This type of measure has already been developed, notably with regard to fisheries, in the context of the Northwest Atlantic Fisheries Organization , though it is above all provided for by the Fish Stocks Agreement (FSA). The FSA  enables Member States of a Regional Fisheries Organization (RFO) to carry out checks of fishing vessels in the area under their authority if they are flying the flag of a State party to the FSA, even if it is not a party to the regional agreement concerned. These vessels must therefore comply with the fisheries rules adopted by the RFO in the area over which it has jurisdiction. However, this regional organization must have adopted binding rules like those laid down by the GFCM and the ICCAT*. This type of agreement allows for mutual assistance in terms of means and a larger number of controls, and thus theoretically encourages more widespread compliance and a higher level of effectiveness of the rule of law. It should, however, be noted that sanctions resulting from a control revealing an infringement of the law are always the responsibility of the flag State (which will find it hard to show any laxity in front of its partners, in the event of illegal behaviour on the part of vessels flying its flag).
 FSA, article 21. http://treaties.un.org/doc/publication/UNTS/Volume%202167/v2167.pdf (p. 154).