The principal purpose of fishery regulations and controls is to ensure a high but sustainable yield to the fishery. Fishing not only causes a reduction in fish population; it also alters the growth rate, the population structure, and has an adverse effect on the normal reproductive capacity of the population (Nikolskii, 1969). It is therefore necessary to have some measures to control fishing in order to ensure the optimum utilization of the resources and reasonable economic returns to the fishermen.
Winberg and Bauer (1971) pointed out that an important factor in creating high productivity of valuable fishes is the regulation of fish stocks by means of protective measures such as closed areas and seasons, control of mesh size or size limit, and restriction of fishing gears. In large water bodies, yearly limits for the catch (catch-quota) of most valuable fishes are based on scientific information of population abundance, growth, recruitment and mortality rates, relationship between catch from a stock and the amount of fishing, and the size of fish at first capture (Dill and Pillay, 1968). Effective measures for the control of fishing and protection of valuable fishes in inland waters may fall into four categories:
Closed areas and closed seasons to establish localities and times of the year when fish must not be taken.
Regulation of the minimum size of fish caught, particularly by controlling the mesh size of the fishing gear.
Limitation of entry by limiting the numbers of fishermen and/or fishing units.
Prohibited destructive fishing activities by prohibition of the use of explosives, toxicants (poisoning), and certain other destructive fishing methods.
However, the determination of the suitability of these regulatory measures has to be judged against economic and sociological conditions. They should be recommended and established only when the need for them has been determined and the effect of such measures estimated and found essentially practicable.
The closure of areas to fishing and establishment of closed seasons can effectively increase the yield by increasing recruitment and reducing fishing mortality. Fishing should be prohibited in the main spawning grounds of valuable fishes during the spawning period and in the feeding grounds of the young. Control of spawning areas and feeding sites of fry and immature fish is intended to allow spawning and also the growth of the fry to the stage when they leave the areas. This is particularly important for lithophilous and phytophilous fish, since spawning may be disrupted and eggs and fry destroyed if fishing is allowed at the wrong time (Nikolskii, 1969). The correct decision on dates allowing fishing operations is very important and may vary for each species and different areas. It also varies from year to year according to climatic conditions and ecological conditions of a water body.
Modifications of seasonal and area closures can be a real advantage in the management of multispecies fisheries. If the proportions of different species caught vary from area to area, or from season to season in the same area, proper regulations can ensure the most valuable combination of species in the final catch (Anderson, 1977).
Such regulations have been accepted in some Asian freshwater fisheries. Fishing in Lake Jatiluhur in Indonesia is prohibited during September and October, and throughout the year for a sanctuary section (Sarnita, 1977). In India, fishing is closed from June or July to the end of September for all large reservoirs. Jhingran (1975) pointed out that the minimum mesh size permitted for nets is generally not less than 30 mm bar-size. In some regions such as the Madhya Pradesh, the State Government prohibits fisheries in reservoirs from 16 June to 15 August (Dubey and Chatterjee, 1977). Establishment of sanctuaries and prohibition of fishing below the dam up to a distance of 3.2 km (2 mi) were generally
In some cases the closure of areas and a closed season for reservoir fisheries in Southeast Asia and the Indian sub-continent may not be necessary, particularly in reservoirs where the fisheries depends on multispecies fishes of short life-span. Most of them can reach maturation within one year and their spawning may extend over up to 3–4 months (throughout the rainy season). Fernando (pers.comm.) pointed out that in reservoirs with lacustrine species and more or less continuous breeding, fishing restriction may not be necessary. For instance, the reservoir Parakrama Samudra in Sri Lanka has had year-round fishing and high yields for over 20 years (de Silva and Fernando, 1979). But control of fishing is required for those fish with a limited breeding period. In Thai reservoirs several species spawn throughout the year. It may be difficult or impossible to set a closed season and area for one species without causing damage to other species. In case of the reservoirs in Thailand, fishing is usually permitted all year round. Closed areas and closed seasons may be considered as very important for a reservoir whose fisheries is based only on a few species. In such reservoirs, which are usually big, fish such as the Indian major carps in Indian reservoirs, require several years to reach maturity. However, it is different in the case of Sri Lanka where the reservoir fisheries is based mainly on Tilapia. There, fishing is permitted throughout the year, resulting in high yields for years. Therefore, these measures as a tool for reservoir fishery management must be considered carefully before applying them. Several factors should be taken into account including species composition of fishes, their life-history, fishing activities and types of fishing gear used, climate, fertility of impounded water, etc. Sound basic data will facilitate the decisions to be made.
The establishment of minimum size is considered an important control measure, particularly for fishes whose reproductive capacity is low. Thus a limiting minimum size will not only protect immature fish, but should be large enough to protect first spawning fish.
Regulation of mesh size has been widely used for controlling the minimum commercial size in protected fish populations because it does not affect the cost of fishing (Dill and Pillay, ~ 1968). However (where the fishing depends on multispecies resources) it is difficult to design appropriate mesh size regulations to ensure adequate protection for valuable fish and permit catches of low value species (Tyurin, 1968). In most instances these two requirements are contradictory because a mesh large enough to allow one species to grow to optimal size may permit practically all of another species to escape permanently. A smaller size, on the other hand, will reduce or even destroy the stock of the first species while allowing a reasonable catch in the second (Anderson, 1977). Therefore, it has to be decided whether it is more harmful to remove some of the young of the protected fishes or to contaminate the water with fishes of little or no value.
The application of this measure must be considered carefully in reservoirs where the fisheries depends on multispecies of fishes because it is impossible to set a proper size limit suited for all species. Limited size may not work as desired, and it may lead to the establishment of small size fishes. On the other hand, this measure may be a very useful one for fishery management in a reservoir whose fisheries depends on only a few economically valuable species such as the Indian major carp fisheries in Indian reservoirs.
This type of regulation does not usually restrict freshwater capture fisheries in Asia and the Far East where most reservoirs have a multispecies fish stock. Dubey and Chatterjee (1977) reported that the State Government of Madhya Pradesh, India, prohibits the catch in reservoirs of mrigal, rohu and calbasu of less than 1 kg in weight, and of catla of less than 4 kg in weight. Srinivasan and Sreenivasan (1976) also reported that the capture of major carps less than 15 cm in length is prohibited in rivers, tanks and reservoirs. In Thailand, mesh of less than 20 mm bar-size is prohibited for fishing in lakes and reservoirs.
This regulation includes restrictions on the number of fishermen and fishing gears, imposition of quotas, taxation and licensing. These measures aim at promoting the conservation and the sustained yield management of a fishery resource since it not only allocates the resource, but also affects the size of the harvest (Adasiak, 1979). The restrictions on the number of fishermen and gears will directly reduce the total fishing effort. Quotas will shorten the fishing season by establishing a total allowable catch for a given period. This practice will arrest overfishing and lead to the recovery of badly depressed stocks. Taxes and licenses will result in a reduction of fishing pressure and help protect the fish stocks from overfishing and depletion.
Limitation of entry should be applied only to a reservoir with intensive fisheries and with data indicating that the fish stock has been utilized up to the maximum potential level. In the reservoirs of Southeast Asia a limitation of entry has not yet been applied.
Restriction of fishing methods generally takes the form of prohibition of or limits on the use of damaging methods and gears and implements, or mesh size limits (Dill and Pillay, 1968). Such restrictions are warranted when increased fishing effort will affect recruitment. Use of poisons and explosives must be prohibited since they are likely to indiscriminately kill fish without regard to species and sizes, endangering the existence of the fish stock, and providing at one time more fish than can be consumed. They are also likely to cause other and often long-lasting damage to the local ecosystem (Gulland, 1974). Other methods of fishing whose harmfulness is generally recognized in inland waters are twin trawls and deep-water sweepnets among which particularly those with fine mesh should be restricted (Tyurin, 1968). Such danger already exists in some lakes such as Lake Victoria and Lake Malawi, where industrial trawling for multispecies cichlid stocks caused a severe overfishing of some species (Welcomme and Henderson, 1976).
Prohibition of use of poisons and explosives is the most common management measure applied to reservoir fisheries in Southeast Asia. Mesh size regulation has been applied only on a limited scale, but trawls are prohibited in Southeast Asia reservoirs.
