- Artisanal (subsistence) aquaculture has been around a long time.
- Generally low-intensity culture that relied on natural sources of propagules, water, and food, e.g. low-intensity shrimp culture in tropical areas, with yields of 0.1 kg m-2 y-1.
- Modern aquaculture involves extremely high densities of organisms (e.g. shrimp yields > 3 kg m-2 yr-1) , and consequently requires heavy supplementation of natural supplies of propagules, water, and food.
- Modern aquacultural techniquesinvolve care for organisms at a range of life-stages:
- Hatcheries – fertilize and hatch eggs of local native species rear the young until they are suitable for release. Generally government-sponsored, in an effort to supplement the abundance of natural stocks.
- Ranching – applies to salmon. Involves hatching eggs and rearing young in a manner that imprints them on a privately controlled homing area, then releasing them to go out to sea and grow up. When they mature they will return to the homing area, where they can be harvested. A privatization of the public hatchery system.
- Cage or pond rearing – fish or crustaceans are moved from a hatchery to rearing cages and held at high densities until they have grown to marketable size.
- Aquaculture has been looked at as a potential source of valuable protein that might perhaps help substitute for declines in harvests from wild stocks that have been overexploited or damaged by pollution.
- Shrimp culture in tropical countries and salmon culture in northern latitudes are two major aquaculture industries that expanded quickly in the 80’s. Mollusk culture and seaweed culture are also expanding rapidly. The industry has been running long enough so that certain problems are becoming clear.
Current problems in modern aquaculture
- Escape of aquaculture organisms and contamination of wild gene pools. Escapees from cage culture operations in Europe now outnumber wild individuals in spawning streams in Europe and Scandinavia. This situation may be disrupting the coevolution between local stocks and local conditions. Norweigan Atlantic salmon escapees from salmon farms are now breeding in all major B.C. salmon streams.
- Local environmental degradation resulting from faecal wastes, unused food, and antibiotic drugs used to control disease and parasitism. Also disturbance of water tables and acidification of cleared land are important in some operations.
- Disease. Over 70% of the world-beating Taiwan shrimp culture industry was recently shut down because of disease problems.
- Escalating costs and falling product prices – increased supply of reared organisms drops the price, and increased demands for food and equipment has escalated costs. This leads to pressure for even higher yields.
Current developments in aquaculture
- Genetic engineering and breeding programs are resulting in impressive gains in production rates; conferring disease resistance is also targeted.
- Techniques for disease control and optimizing rearing conditions are being sought.
- Methods for the production of sterile individuals that can’t interbreed with wild stocks are being developed. These non-sexual stocks have substantially higher growth rates than wild sexually-reproducing stocks.
- Environmental limits have been approached and exceeded in many locations. The environmental impacts of rapidly expanding aquaculture are now being recognized, and techniques for their moderation are under study.
Can intensive aquaculture replace the supply of protein from wild fish stocks?
- Example of semi-intensive shrimp culture (a major industry in tropical countries) as described in Flaherty and Karnjanakesorn. 1995. Marine shrimp aquaculture and natural resource degradation in Thailand. Environ. Manage. 19:27-37; Larsson, et al. 1994. Ecological limitations and appropriation of ecosystem support by shrimp farming in Colombia. Environ. Manage. 18:663:676.)’
- Artisinal shrimp farming involved almost no human inputs beyond the energy to harvest the mature shrimp. Natural invasion of young shrimp to tidally flushed ponds that produced their own shrimp food were used. Semi-intensive and intensive shrimp culture operate with much higher shrimp densities that require addition of food and much additional water input that requires pumps, aerators, and filters, and degrades nearby waters with runoff.
- One way of measuring the effectiveness of aquaculture is to determine its “ecological footprint” – the area of land required to supply all the needs of a hectare of aquaculture.
- One hectare of semiintensive shrimp farming requires an area of ecosystem support that is 75-190 times as large as the farm itself:
- -50-160 ha of coastal mangrove marsh to produce the shrimp larvae to seed the ponds (exact number depends on natural productivity of the marsh
- -7.2 ha of mangrove lagoons with which to exchange water
- -4.2 ha of mangroves to produce the detritus portion of shrimp diet
- -14.5 ha of marine ecosystem to produce the fish meal used in shrimp food
- -0.5 ha of agriculture ecosystems to produce the cereal grains in shrimp food
- -0.8-2.5 ha of CO2-sequestering forest to fix the CO2 released in fossil fuels used to rear shrimp and to obtain and manufacture shrimp food
- This large ecological footprint leads to the conclusion that, although there are many acres of mangrove marsh that could still be converted to shrimp culture in Colombia, the surrounding ecosystem support required is large enough that the present level of shrimp farming there is just about fully-exploiting the area of mangroves that can produce larvae for culture. Further expansion could lead to severe deterioration of rearing success like that which has been experienced in countries where aquaculture development was more intensive.
Comparison of current aquaculture practices with other food production systems:
|Best sea ranching techniques for
|Rangeland beef farming||10|
|Trawler fishing of wild cod
|Fishing wild Atlantic salmon||29|
|Semiintensive shrimp farming||40|
|Cage-farming of Atlantic salmon||50|
- The most rapidly developing aquaculture methods are extremely inefficient in comparison to terrestrial food production methods.
- The only thing that sustains the intensive shrimp farming and cage salmon farming methods is the premium price well-to-do buyers are willing to pay. As a way of rearing food, current aquaculture methods are much more costly in terms of both dollars and environmental impact than sustainable exploitation of natural fish stocks.
- The most efficient aquaculture methods (e.g. salmon ranching) depend on the continued existence of high quality, pollution-free aquatic habitats that are in the public domain.
- Major improvements in the efficiency of most aquaculture programs are required before they can be considered as an effective means of meeting the world’s demand for protein.
Notes on the video “Taking Stock” (National Film Board)
- Cod fishery persisted as an artisanal fishery for 400+ years.
- Introduction of steam power and larger boats led to offshore harvest by international fleet that imperilled stocks in 1950’s and 60’s.
- Declaration of 200-mile limit in 1970’s brought almost all of the Grand Banks fishing grounds under exclusively Canadian control.
- Governments promoted offshore trawler fishery as a means of developing a year-round market for cod and providing steady employment for maritimers.
- Inshore fishermen began to see signs of stock declines in early 1980’s but offshore catches remained high.
- By the mid 1980’s government researchers began to think something in the stock had changed, but there was too much year-to-year variation and not enough historical data to be sure. All they had to go on was catch-per-effort, and effort was changing in ways they could not measure.
- Scientists’ uncertainties and declines in inshore catch were not sufficient to motivate politicians to take the difficult decision to reduce quotas.
- After several years scientists and inshore fishers finally convinced politicians that drastic action must be taken. Fishery was closed by the national government.
- -Fishers blamed government for mismanagement of the resource.