aquaculture

The FAO have published a report Preliminary Stock Assessment for the Shallow Water Shrimp Trawl Fishery of Tanzania based on catch and effort data for 1988. The report focuses on trawl fishing rather than farming, but it gives valuable indications in terms of times and conditions.

Issues related to the establishment of prawn farms in Tanzania, with an example from the Rufiji delta are available in this report published by the Mangrove Management Project, Forestry and Beekeeping Division of the Institute of Resource Assessment, University of Dar es Salaam.

A giant prawn farm to expropriate one third of the mangroves of the Rufiji Delta has recently been proposed by a private developer, the East African Fishing Company Limited, a subsidiary of TANNOL Holdings Ltd. Prawn farms have over the past 5 – 6 years been proposed for various locations along the Tanzanian coast, but none have so far been established.

This has generally been due to shortfalls in addressing social and environmental issues; issues often raised in Environmental Impact Assessments. The decisions not to approve projects have mostly been taken by funding or credit agencies and have rested upon experiences from similar projects in other countries where prawn farming has been practised in Asia and America. Both the positive and negative impacts of establishing large scale prawn farming are well documented in global literature.

The FOA have a published report (1997) as part of the support to the special plan for prawn and shrimp farming about Site Selection Towards Sustainable Shrimp Aquaculture in Myanmar. The executive summary notes: Shrimp culture in Myanmar is as yet little developed. Out of an estimated potential area of 48,000 ha, only 16,000 are used for traditional and extensive culture. A mere 80 ha use semi-intensive culture. Rakhine State predominates with 97% of the culture area.

Shrimp culture is expected to expand rapidly with the introduction of semi-intensive shrimp farming technology transferred from Indonesia. To avoid serious environmental and shrimp disease problems which have plagued other ASEAN shrimp producers, environmental impact assessment and best management practices (BMP) should be introduced.

The outstanding issues generated by semi-intensive shrimp farm development are:
1. Destruction of mangrove forest ecosystem
2. Deterioration in water quality
3. Land allocation
4. Economic losses through disease and poor management.

Sustainable shrimp aquaculture rests on a healthy mangrove ecosystem. It should not be forgotten that the mangrove forest is the nursery ground for cultured shrimp species, whose genetic diversity forms the basis of the shrimp aquaculture industry.

Uncontrolled destruction of the mangrove ecosystem will lead to reduced breeding stocks of major cultured species. Not only will genetic diversity decline, but spawners and brood stock will become increasingly difficult to catch.

Shrimp farming depends upon high water quality. Mangroves and the biota associated with them are a natural biofilter, removing excess nutrients and sediments discharged by shrimp farms. Mangroves protect shorelines from erosion and are very effective storm breaks.

Tan Cheng Li, writing in the August 30, 2005 edition of the thestar.com.my, comments that nations hit by the December 26 tsunami are now planting mangrove trees along coastlines to create ‘greenbelts’ or vegetated strips of land, in the hope of preventing further erosion of damaged shores as well as to shield them from future giant waves.

Mangroves are something of a rarity – they cover a mere 0.04% of Earth’s surface and 0.12% of its land area, and whatever mangrove resource that remains should be conserved. There is an economic benefit to this as well.

In Malaysia, it costs RM15,000 to replant one hectare of mangroves. The government has identified 4,016ha of degraded mangroves requiring rehabilitation at a cost of RM110mil. Some 151ha have been replanted so far.

Impact of the tsunami
The December 26 tsunami left behind extensive environmental damage across the region. It totally changed coastal landscapes and ecosystems. The impact included:
# Loss and degradation of mangrove and seagrass beds
# Silting and degradation of coral reefs
# Change in tidal flats and coastal lagoons
# Uplifting of the seafloor in some areas
# Turbid coastal water
# Scouring of coastline
# Inland deposition of sand
# Salination of coastal land
# Impact on fisheries

The role of mangroves during the tsunami:
# Reflect and resist tsunami energy, thus reducing the inundation depth and area.
# Trap driftwood and other debris, thus reducing human injuries and property damage.
# Prevent people from being washed out to sea.
# Reduce erosion of beaches and sand dunes which also act as barriers to tsunamis.

Research has been done into integrating mangroves and aquaculture into sustainable aquaculture-silvoculture systems.

Silvofisheries is a form of integrated mangrove tree culture with brackishwater aquaculture. It is a form of low input sustainable aquaculture. This integrated approach to conservation and utilization of the mangrove resource allows for maintaining a relatively high level of integrity in the mangrove area while capitalizing on the economic benefits of brackishwater aquaculture. Further extension of aquaculture to meet the needs of the rural poor may be tolerable provided it is carried out in a controlled manner outside those areas already heavily exploited and environmentally sensitive in an integrated program of conservation and utilization, such as silvofishery methods.

Research has also been conducted into Disused Shrimp Ponds: Options for Redevelopment of Mangrove. N.J. Stevenson describes that associated with the rapid increase in the production of cultured marine shrimp, has been large scale conversion of mangrove to shrimp ponds. Production in many regions has proven to be unsustainable, largely due to inappropriate construction methods, poor environmental conditions, overstocking and disease problems. A number of shrimp ponds are consequently unproductive and lie idle. Accurate assessments of pond disuse are difficult to obtain, however, unofficial estimates have suggested that as many as 70% of ponds may be disused after a period in production. Pond construction, shrimp culture and pond disuse lead to alterations to the physical and chemical properties of soil, hydrological conditions and the flora and fauna composition of the pond area. The case for restoration, or rehabilitation to a sustainable use, is strong. Consideration must be given to the causes of production failure, the environmental conditions remaining following disuse, the needs and preferences of pond owners and coastal managers, and technical constraints.

It could be considered to be quite unusual to find an academic from a scientific discipline to have a flair for the aesthetic. Luis Rocha manages the combination with aplomb. He has created a web site about coral reef fishes superbly illustrated with his own photographs.

Rocha explains some of the attractions of coral reefs:

The most striking feature of reef fish is their diversity, in terms of both species number and the range of morphologies. An estimated 4000 (18% of all living fishes) species of fish live on coral reefs and associated habitats of the Indo-Pacific and Atlantic oceans, and this number increases as new exploratory surveys are done.

Further examples of his reef fish photographs can be found at his online gallery. As might be expected from his scientific background, the photographs are not only beautiful, they are meticulously accurate.

There’s an interesting range of information available on the net relating to controlling algae with barley straw. The UK Centre for Aquatic Plant Management have developed a number of methods of dealing with aquatic and riparian plants, including a novel method of controlling algae. They have published a report describing the application of barley straw to water. The method has had widespread international testing and has proved to be very successful in most situations with no known undesirable side-effects. It offers a cheap, environmentally acceptable way of controlling algae in water bodies ranging in size from garden ponds to large reservoirs, streams, rivers and lakes.

The Maryland Aquafarmer has researched the use of barley straw to control pond algae and their findings are inconclusive. In laboratory studies, some types of algae could be controlled effectively by barley straw extracts, but the main target, green mat-forming algae, did not seem to be inhibited. However, barley straw did control several species of microscopic algae that often cause unusual odors or flavor in pond-cultured products. Follow-up studies found that some dinoflagellates – the single-celled phytoplankton that have been associated with fish death – are inhibited by barley straw.

Further to using barley straw to inhibit odor causing algae, a two-year project jointly funded by Australian Pork Limited and the Queensland Department of Primary Industries and Fisheries found that supported barley straw covers were effective in reducing odour emissions by up to 90% from anaerobic piggery effluent ponds.