Terminology (EIFAC Technical Paper No. 44, 1984)
Introduction: Any species intentionally or accidentally transported and released by man into an environment outside its present range.
Transferred species: Any species intentionally or accidentally transported and released within its present range.
Stocking: The intentional release of aquatic organisms with the aim of utilizing the natural biological productivity of natural or artificial waters such as reservoirs other than fish farm ponds or other intensive units.
Purposes of stocking
Compensation: To provide for a phase in the life cycle suppressed by human intervention (the stock would disappear without stocking)
Maintenance: To sustain stocks in face of environmental or fishing pressures which prevent their attaining the natural carrying capacity.
Enhancement: To keep the production of stocks above the level that would be naturally sustained in the presence of heavy exploitation.
Put-and-take: To provide catchable-sized fish for rapid exploitation by anglers (minimal environmental input).
Put-grow-and-take: To provide fish that must grow to a catchable size before exploitation by anglers (some environmental input).
Re-population: Establishment of a unit stock of community in waters from which it has previously been eliminated.
Increase diversity: To augment the range of species available to a fishery.
Niche filling: To provide stocks for utilizing a trophic or spatial resource which is perceived as unexploited.
Forage: To provide a prey species for enhancing the production of angling or commercially exploited species.
Pest control: To provide organisms for controlling flora or fauna perceived as unfavourable to man.
Environmental improvement: To provide organisms expected to favourably modify the system.
Conservation: To maintain genetic diversity (as to conserve endangered species or stocks).
Nomenclature for developmental interval terms of coregonids used in this paper:
Fertilized eggs: The phase between fertilization of the eggs and hatching.
Yolk-sac-larva: The phase between hatching and absorption of the yolk.
Larva: The phase between first feeding and acquisition of the minimum complement of adult fin rays1
Juvenile: The phase between the complement of adult fin rays and sexual maturity (these can be further classified as summer juveniles, autumn juveniles, etc., or on the basis of their size)
Adult: The phase between the attainment of sexual maturity and old age (used generally in connection with transfer of fish)
1 In practice larvae are usually stocked when they are first fed.
Model for stocking juvenile whitefish in Finnish lakes
Many factors affect the yield from whitefish juvenile stocking, but the two most important variables according to multiple regression analysis are the fishing effort (measured by the number of gill nets used for whitefish fishing) and the stocking rate (F2,37 = 28.06; P<0.0001; R2 = 0.60).
The yield from stocking can be increased both by increasing the fishing effort and by stocking more juveniles up to 30 individuals/ha.
From a fisheries management point of view it is better to vary the fishing effort. Increasing the fishing effort gives a higher yield/1000 stocked juveniles and more income from selling gill net licences. Increasing the stocking rate causes higher costs and lower yield/1000 stocked juveniles if the fishing effort is stable.
A relatively high fishing effort is also important because it releases compensatory processes; e.g. the individual growth rate increases, which leads to a more valuable catch.
It is not advisable to increase the stocking rate more often than every 5 years, but the fishing effort can be adjusted on an annual basis.
The yield from stocking cannot be increased indefinitely by increasing the fishing effort, because the growth potential of whitefish is limited and some of the stocked whitefish always die of natural causes. All the known results of whitefish juvenile stocking have been < 500 kg/1000 stocked juveniles.
The population density should be relatively high (catchable stock size) for successful fishing. The stocking rate and fishing effort should be adjusted so that the yield/1000 stocked juveniles is roughly 75–150 kg.
IMPLEMENTATION PLAN FOR STOCKING/FROM TO
Place of stocking:
Fisheries district: Fisheries area:
Owner of the water area: Water area:
Surface area: ha Type of water:
Present fishing:
Professional fishermen: Subsistence fishermen:
Recreational fishermen: Coregonid catch: kg/ha
Gear units: units Applicable for coregonids: units
Fisheries management objectives:
Objectives for stocking:
Target yield: kg/ha Fishing effort: nets/ha
Other objectives:
Stocking material:
Whitefish form: Age: Size:
No. of fingerlings needed: Stocking density: ind./ha
Price of fingerlings: /ind.
Hatchery/pond etc.:
Health control:
Stocking:
Timing: Place:
Person in charge of the stocking:
Profitability:
Value of catch Price of fingerlings
Licence fees Transportation costs
Other benefits Other costs
Sum of benefits Sum of costs
BENEFIT-COST RATIO:
Social benefits:
Organization of monitoring:
The plan accepted by:
Fisheries district:
Fisheries area:
Owner of the water area:
Planned by:
REFERENCES
Bninska M. and M. Leopold, 1990. Fisheries management in Polish lakes. In: W.L.T. van Densen, B. Steinmetz & R.H. Hughes (eds). Management of freshwater fisheries. Proceedings of a symposium organized by the European Inland Fisheries Advisory Commission, Goteborg, Sweden 31 May-3 June 1988. Pudoc. Wageningen pp 406–436.
Hartmann J. 1988. 1st die Rekrutierung (Jahrgangsstarke) beim Bodenseefelchen (Coregonus lavaretus) schon verstanden? Osterreichs Fischerei 41. p. 135–142.
Muller R. 1990. Management practices for lake fisheries in Switzerland. In: W.L.T. van Densen, B. Steinmetz & R.H. Hughes (eds). Management of freshwater fisheries. Proceedings of a symposium organized by the European Inland Fisheries Advisory Commission, Goteborg, Sweden 31 May-3 June 1988. Pudoc. Wageningen pp 477–492.
Salojarvi K. 1992. The role of compensatory processes in determining the yield from whitefish (Coregonus lavaretus L. s.l.) stocking in inland waters in Northern Finland. Finnish Fisheries Research 13. p 1–30.
Svardson G. 1976. Interspecific population dominance in fish communities in Scandinavian lakes. Rep. Inst. Freshwater Res. Drottningholm 55. p 144–171.
Szczeerbowski J. 1977. Effectiveness of stocking lakes with lake whitefish. Efekywnosc zarybinia jezior sieja Rocz. Nauk Roln. Ser. H. 98(2), p 117–133.
Todd T.N. 1983. The feasibility of mass-culturing coregonines in the Great Lakes. Research Completion Report 179p (mimeo).
