Cultivation racks for mussels (Thau, France)
In contrast to aquaculture sensu stricto which involves the cultivation of aquatic life within controlled environments or the commercial production of certain aquatic species by managing the major part of their life history under strict control, culture-based fisheries increase production in natural environments by controlling a part of the life history of certain species and transplanting or releasing their seed or fry into the open waters. The juvenile fish, which are produced in hatcheries and are released into fresh- brackish- or marine waters, are allowed to propagate or grow on natural foods until they reach harvestable size.
Culture-based fisheries are less limited by land or population pressures and do not have to modify or manage the culture system to approximate the natural environment since it uses the natural environment itself. However, unlike aquaculture, harvests are uncertain and returns are more difficult to predict, depending as they are on the quality of fingerlings released and their survival in an uncontrolled environment.
Nonetheless, culture-based fisheries have been increasingly resorted to as means of enhancing the fishery resources, replenishing natural stocks whose populations have declined through over-exploitation or environmental degradation, or simply maximizing the productivity of open bays, coastal lagoons, or freshwater reservoirs. Their adoption or application on an expanded scale has in fact been identified as a high-priority item in the agenda for development in a number of regions in the world in the coming years despite some serious scientific reservations about the effectiveness of the approach (see topic on enhancement.
The major types of culture-based fisheries include:
Sea ranching, in which juvenile fish are released to grow unprotected on natural foods in marine waters where they are harvested at marketable size, takes advantage of the sea as a large aquatic pasture. While it is practised in slightly differing forms around the world, in its distinctive form, young fish are released to the sea through ponds, enclosures or channels, and allowed to grow until they are ready for the market.
Sea ranching of salmon is widely practised in countries such as the United States (mainly Alaska, Washington and Oregon), Canada, Japan, USSR, New Zealand, Iceland, and the Baltic countries. The most widely used species for ocean ranching is the Pacific salmon (Oncorhynchus sp.) because of the success of its artificial spawning coupled with the rapid growth and the high degree of its homing precision that makes it amenable to harvesting at maturity. The practice of salmon ranching existed already a century ago or more in the Nordic countries and USA and Japan, where it really took of in the early 1960s. Pink and chum salmon are raised in Soviet hatcheries using technology similar to that of Japan. In the Pacific Northwest, chinook and coho salmon are the predominant species used in hatcheries where raceways and ponds for feeding juvenile fish are prominently featured.
Canada's salmon farming industry has grown tremendously in the mid 1980s as a result of its successful hatchery operations. Canadian hatchery workers have pioneered development and application of spawning and egg incubation channels which provide favourable environmental conditions for eggs and fingerlings. These techniques have been applied most successfully to sockeye, pink and chum salmon.
Aside from the widely popular Pacific salmon, other marine species have been used for ocean ranching in the Seto inland sea of Japan: Kuruma prawn, red sea bream, blue crabs, sole, flounder, and yellowtail supported by the development of a large number of Prefectural Centers for Culture-Based Fisheries all over Japan. The Ezo abalone, Haliotis discus Hanai, is one of the most important species for ocean ranching in Japan in rocky areas of the Sea of Japan around Hokkaido. Likewise, the giant Ezo scallop, Patinopecten yessoensis, is propagated in the Okhotsk Sea, the Nemuro Channel, and in other areas of the Hokkaido coast.
Coastal lagoon farming
Extensive lagoon farming is a traditional activity in various European and Mediterranean countries. Brush parks are used in many countries of Africa.
Valliculture, as the practice is called in view of its being fish culture-based, is one of the most ancient forms of aquaculture in the Mediterranean region. Its origins date back to the first rudimental fish pond and fattening systems used along the Adriatic and Tyrrhenian coasts. This technique was developed by the upper Adriatic populations to exploit the seasonal migrations of some fish species from the sea into the lagoon and delta areas which were more suitable for their growth. Among the Mediterranean countries, Italy has the largest areas of brackish water (called "valli") that are exploited for lagoon farming of commercially valuable species like Anguilla anguilla, Mugil cephalus, Liza aurata, Liza saliens, Liza ramada, Chelon labrosus, Dicentrarchus labrax and Sparus aurata. Restocking of the valli/coastal lagoons is carried out by anadromous, natural, and annual migration and by artificial restocking. Catches from the valli primarily depend on the quantity of fingerlings which entered the lagoons some years before and on the quantity of fingerlings stocked.
These species used to return to the sea in order to avoid unfavourable environmental conditions or for reproduction. To exploit these periodic movements, large brackish areas were enclosed to prevent the fish returning to the sea and complex permanent capture systems, fish barriers, were developed consisting of barriers in the channels communicating with the sea to catch the adults. Later, from the simple ponding of fry freely entering the lagoon from the sea, came a man-made seeding of fry fished elsewhere and introduced into the basins to be reared for a few years.
Brush-park fishery in Benin
The successful management of coastal lagoons using hatchery-bred fry of important species is thought to hold considerable promise world-wide for expansion in the future.
Brush-park fisheries are a traditional form of low-technology aquaculture which is practised in coastal lagoons and brackish waters in many areas of the world. The brush parks are constructed in a variety of forms and sizes, but basically a brush park consists of an inner core, or concentric circles, of densely packed tree branches or other material surrounded by an outer, more substantial wooden framework which is fished periodically, usually by encirclement.
In coastal lagoons the most sophisticated forms of brush-park fisheries occur in Benin. There are several basic types of brush-park fisheries in Benin where they are known collectively as "acadjas". They vary from each other in configuration, construction and fishing characteristics. The acadjas are constructed of tree branches with harder woods forming the peripheral structure and with soft wood branches with many ramifications forming the interior of the acadja. Acadjas are preferentially placed in shallow, quiet waters of no more than 1.5 m depth.
Fishing is accomplished by surrounding the smaller types of acadjas with a net after which all of the branches are removed and the net is then pursed. For the larger brush parks the surrounding net is fished in a step-wise process by gradually moving the net inwards as branches are removed until the fish are concentrated in small areas and can thus be removed with traps, baskets, and hand-nets. After fishing, the used branches are replaced and new ones added as necessary.
Elsewhere in Africa, brush-park fisheries are found in coastal lagoons in Nigeria, Côte d'Ivoire, Ghana, Togo and Madagascar. Elsewhere in the world, brush-park fisheries are found in Negombo lagoon in Sri Lanka and have been introduced in some Mexican lagoons.
Stocking of inland waters
Among the most advocated and widely used practices for the management of the fisheries resources of lakes and reservoirs throughout the world is the stocking and recapture technique.
Species stocked are either indigenous or exotic and either herbivorous, carnivorous, or omnivorous. In tropical developing countries, where the production of more fish for food is the goal of any fisheries activity, high-yielding herbivores, detritivores and plankton feeders (like tilapia and carp), are commonly stocked in lakes and reservoirs. This is in direct contrast with the developed countries in temperate zones where carnivores like trout and bass are stocked in lakes and reservoirs to support the recreational or sport fishery. The major lakes and reservoirs in ASEAN countries, for example, have been stocked with hatchery-produced fingerlings of a wide variety of species including tilapia, various Chinese and Indian major carps, milkfish, mullet and catfish.
In China, around 65%, or 1.4 million ha, of reservoir area out of a total of two million ha were farmed towards the end of the 1980s. They are stocked with fingerlings and following a period of growth mature fish are harvested. The species used are the common carp, grass carp, silver carp, bighead carp, mud carp, and Wuchang bream (Megalobrama amblycephala) in varying densities and species ratios. Reservoir fisheries in China are almost entirely dependent on the regular release of large quantities of fingerlings because the Chinese carp does not spawn outside its area of origin.
In Israel, many water storage reservoirs (10-40 ha area, 5-7 m depth) originally constructed for irrigation, are now stocked with a range of species including tilapia, mullet and carp, usually grown in intensively managed polyculture systems.
Sri Lanka's large perennial reservoirs and small seasonal tanks constitute the country's main freshwater resource. These are regularly stocked with fingerlings of the different carp species (Indian, Chinese, and common) which are produced at Government-run hatcheries spread all over the country. Since the Indian and Chinese carps do not spawn in the reservoirs/tanks, they have to be stocked regularly to sustain the fisheries. There is thus large pressure on the State to accelerate its seed production programme to keep up with the large demand for fingerlings. It is interesting to note that unlike the Philippines and Thailand, for example, where fish seed production is largely a private sector undertaking, the Sri Lankan Ministry of Fisheries is primarily responsible for the production of carp fingerlings for distribution among the various reservoirs and seasonal tanks.
In Cuba, most of the freshwater fish is produced from seeding of the country's small to medium size reservoirs; in Colombia, some dams are stocked and restocked with mullets.
African small reservoirs are stocked mainly with tilapias and Clarias. In Zambia the most important species for stocking reservoirs are Tilapia melanopleura, T. macrochir, T. andersonii, and Haplochromis spp. In Zimbabwe the fish most commonly used for dam stocking are Oreochromis mossambicus, O. macrochir, T. rendalli and several exotics like black bass and rainbow trout.