Stocking of Open Waters and Ranching

Stocking of Open Waters and Ranching

The technologies of aquaculture described relate to growing aquatic animals in confinement. Some of those techniques can be adopted for building up populations of selected species or for enhancing existing populations in open waters such as streams, lakes, reservoirs, lagoons and sea areas. If a suitable anadromous species is selected, the homing behaviour can be utilized to ensure that the surviving stock from releases return to the home waters for spawning, after ranching in the open seas. The main advantage in stocking and ranching is the elimination of the controlled grow-out phase and consequent savings on artificial feeding and stock maintenance, besides the capital costs of grow-out facilities. In both open-water stocking and ranching, the released animals feed on natural food in the environment and are exposed to predators and other causes of mortality which cannot be controlled.

The term ranching is used here only when a species is allowed to forage around freely in extensive water areas like the sea, and is able to return to its home waters at a certain stage of its life.

The need for and value of human intervention in enhancing fishery resources have been demonstrated by the state of natural stocks of a number of aquatic species. Populations of salmon and trout in many rivers which were decimated by excessive fishing or environmental degradation could be rehabilitated only through continued stocking of hatcheryraised young. Many multi-purpose reservoirs formed by damming rivers, where populations of economically important fish species had declined or disappeared due to environmental changes, have developed into major resources of important species by stocking. Even though it is not always easy to measure very precisely the economic return in every case, there is evidence from experience in several instances that adequately planned release of spawners of hatchery-raised young in sufficient numbers for the required periods of time has resulted in remarkable increases in commercial catches. However, it involves considerable expenditure of both money and organized effort for a number of years to yield noticeable results. It is also necessary to grow the animal before release to a size at which it can fend for itself, in order to reduce mortality due to predation. The lack of success of some of the earlier efforts of population enhancement could have been because these requirements were not fulfilled.