Whatever indirect measure of fishing mortality is used, there remains a choice in the way the amount is controlled. If the mortality is higher than desired, then the amount can be reduced in several ways.
(i) stop everyone from fishing for some of the time
(ii) stop some people from fishing for all the time (limited entry)
(iii) allow all to fish all the time (or most of the time) but limit the efficiency of operations
(iv) some combination of these
The third of these clearly prevents the costs of fishing to be reduced in proportion to the reduction of fishing mortality, and thus loses much of the possible benefit of regulations. However, in one form or another (prohibitions on trawling, on the use of monofilament gill-nets, limitations on the size of ship) such methods have been widely used, especially in national programmes of fishery management.
Restrictions on gear efficiency may be of value when other regulations giving greater economic benefit cannot be employed. For instance, whenever the yield/effort declines sharply beyond some maximum point (e.g. in the simple Schaefer model, or when the recruitment is significantly reduced by reduction in adult stock), there will at least be a gain in total catch by preventing the mortality increasing beyond the value giving the maximum.
There may in some circumstances even be some economic benefit in restricting the type of gear in comparison with having no regulations at all. Suppose a group of fishermen is fully exploiting a stock of fish, and that they have no easily available alternative employment. A new method of fishing - e.g. with purse-seines instead of gill-nets - might give improved efficiency and for an individual fisherman his increased catches would (so long as the others used the old gear) greatly exceed the additional costs of the new gear. However, if all use the new gear (and if one starts the others will have to follow), the long-term effect will be that the same total catch is shared among the same people, who will have the extra costs of the new gear.
The prohibition of the use of the most effective gear may therefore be better than doing nothing, though less desirable than allowing the most effective gear with other methods of regulation - unless the objectives of regulation are, for example, to maximise employment until those displaced can be fitted into other jobs. This method will not be discussed in more detail here.
