Management measures based on fish size or sex attempt to maintain stocks by enhancing their reproductive and growth potential. This type of regulation protects individual fish if they have not yet matured to spawning size or if they are important to reproduction, and it allows fish to be caught at a larger size. Sex and size restrictions are used extensively in crustacean fisheries, such as the West Coast Dungeness and Alaskan snow, Tanner, and king crab fisheries, in which only males with a minimum carapace length can be retained, or the New England lobster fishery, in which only males and non-egg-bearing females above a minimum carapace length may be retained. Minimum fish sizes are frequently used in conjunction with gear restrictions, for example, the minimum size of sablefish combined with a minimum trawl mesh size in the Pacific groundfish trawl fishery. However, minimum fish size rules apply to the retention, not the capture, of undersized fish. Some mortality of undersized fish will result from the process of catching and discarding.
Means of protecting small fish vary from country to country; some make landings of undersized fish illegal so the fish must be thrown overboard at sea, whereas in other countries, all fish—including undersized ones—must be landed (called full retention). If captured fish can survive upon release, which is primarily true for crustaceans, mollusks, finfish without closed swim bladders caught in pot or trap fisheries, and some hook-and-line fisheries, requiring immediate release is the most common practice. Release of undersized fish has no conservation benefits in gillnet or trawl fisheries and may have limited benefit in other fisheries because the undersized fish are likely to be dead when returned to the sea. Enforcement of size and sex regulations may be costly. In addition, regulating for size and sex of fish, while appropriate for biological productivity goals, does nothing to alleviate the race for fish (OECD, 1997).
Area restrictions limit the geographic region within which fishing is permitted. Area closures are usually temporary—expressed as time-area closures—and are focused on specific types of gear or vessels to prevent harvest during spawning, provide nursery areas for juveniles, or protect species during other vulnerable life history stages. Area restrictions are often applied to geographic regions that have particular conservation needs related to spawning, feeding, or preservation of other ecological services. Area restrictions are also used to allow juveniles to grow to a full, more valuable, size.
For example, fishing in the Shelikof Strait area for Gulf of Alaska pollock is prohibited during the spawning season, and trawl gear is kept out of crab or lobster grounds during molting season. In fact, Bristol Bay and large areas above the Alaska Peninsula are permanently closed to trawling to reduce bycatch mor-