English Free Article | Technology | VOL. 12, ISSUE 75, November-December 2012 |

Ocean Technology for Islands

Lakshadweep depends on the mainland for their daily requirements as, apart from engaging in fishing and coconut cultivation, livelihood opportunities are very limited for the islanders. This forms the essence of the struggle for survival for the local populace. Technological developments are yet to reach most of these islands and implementation of solutions for water and energy are hampered by the remoteness and lack of logistic support. Advanced solutions, therefore, are imperative for these islands to achieve a degree of self sufficiency. National Institute of Ocean Technology (NIOT) has been developing a wide spectrum ocean application that are now popular among the local population. Some of these have been highlighted here.

 

Low Temperature Thermal Desalination

Population explosion and over exploitation of ground water resources with little time for recharging poses a severe challenge for the islands of Lakshadweep. The mismatch between increasing water demand and decline in water availability due to overexploitation and climate change is a critical issue for the islanders. Desalination, which is the conversion of seawater to potable water through physical and chemical methods, has emerged as a potential solution worldwide, with cost effectiveness of the methodology and ease of operation being critical for the choice of the technology.

The Lakshadweep Islands in general have a steep bathymetry in its eastern side and achieves a depth of about 400 m within 100-600 m from the shore. The low temperature thermal desalination (LTTD) process uses naturally available temperature difference in the ocean layers to produce potable water and is an extremely environment friendly technology. The process deals with evaporating the warmer surface sea water at low pressures and condensing the resultant pure vapour using deep sea cold water available at about 400 m below sea level. The process is found to be simple and easy to maintain since it requires just a few components – a flash chamber for evaporation, a condenser for liquefying the vapour, sea water pumps, vacuum system, a long pipe to draw cold deep water and associated marine structures.

A desalination plant at Kavaratti with a capacity of 1 lakh litres per day was set up in 2005 on experimental basis using the LTTD technology to alleviate the scarcity of drinking water. The plant is being operated by local islanders since 2006, meeting the drinking water requirements of the 10,000 strong local community for over six years. Studies conducted by a team of doctors have shown an improvement in the public health with a sharp drop in the water borne diseases.

Following the successful operations, the Minicoy Desalination Plant was commissioned in April 2011 while a third at Agatti started its operations from July, 2011.

 

Lobster fattening technology development

Research on lobsters was initiated under the Living Marine Resources Enhancement programme of NIOT in 1999, with particular reference to the development of technologies for lobster breeding, larval rearing, fattening, farming and sea ranching for lobster resource enhancement. Surveys were conducted to evaluate the lobster resources both in the Gulf of Mannar Islands and in the Andaman and Nicobar Islands to obtain baseline data and also to correlate the effect of sea ranching.

NIOT has succeeded in developing captive broodstock of four species of spiny, sand and squat lobsters to produce healthy phyllosoma larvae. By manipulating the environmental condition in the tank and by providing better nutrition the average spawning in the captive broodstock was increased from 1 to 4. As many as 7 spawning in a year was recorded in one of the breeders, the first in a spiny lobster. With captive broodstock there is now considerable scope of completing the life cycle of this highly priced lobster.

 

Open Sea cage culture

The world’s total capture fisheries are estimated to be around 100 million metric tonnes per year. The expected global population of 8.5 billion in 2025 requires 55 million tonnes of additional seafood to meet the WHO recommendation of 13 kg per capita consumption rate. Aquaculture is the only promising method to cope with the increasing demand. At present the global aquaculture production is about 59 million metric tonnes with India contributing only 0.25 (Food and Agriculture Organisation, 2010).

Production of marine fish caged in enclosures has been a relatively recent aquaculture innovation. NIOT with prior experience in deployment of cages, tested open sea cages suitable for the Indian seas. Based on sea conditions NIOT selected a 9 m diameter high density polyethylene (HDPE) cage with multipoint mooring system for the first time in India and deployed it in three locations in different parts of the country. In the absence of a large scale nursery rearing facility, NIOT designed and developed 2 m diameter HDPE cages with nylon knotless mesh (Fig. 1). Hatchery reared seabass fingerlings obtained from Rajiv Gandhi Centre for Aquaculture (RGCA) were reared from 9 g to 30 g in 40 days with 90 per cent survival, in the nursery cages, floated within the cages in the sea. Experiment culture carried out simultaneously in all the three locations revealed that the cages developed can withstand all type of sea conditions of the country.

 

Fish Aggregating Devices

The structures that float on the surface of the ocean attracting both juvenile and adult fish in great numbers and diversity are fish aggregating devices (FADs). Aggregations of fishes have been recorded extensively around both natural drifting objects and man made ones. FADs have traditionally been defined as objects placed in the ocean specifically to attract fish for capture and about 333 fish species belonging to 96 families were found associated with such floating structures. FADs help in increasing the fish catch and at the same time reducing the operational time and fuel cost. Rational use of oceanic FADs can greatly improve the socioeconomic status of the fishers, especially the islanders of Lakshadweep.

NIOT has deployed moored data buoys near to Lakshadweep Islands for the collection of oceanographic and meteorological data which also acted as FADs bringing in fish. NIOT also developed an oceanic FAD indigenously, to be used exclusively to aggregate fish in waters off the islands. Vertical column type FAD, (0.7 m diameter, 3.6 m length) were fabricated with an HDPE extruded pipe with wall thickness of 35 mm, galvanised steel and filled with high density polyurethane foam to increase the buoyancy. The success of the 28 FADs deployed in Lakshadweep prompted the Andaman Administration to request for a similar deployment.

Fig 1: Open sea cage mooring configuration

Fig 1: Open sea cage mooring configuration

Marine micro algae culture

Micro algae are a heterogeneous group of organisms in the aquatic ecosystem and are efficient fixers of solar energy as compared to terrestrial plants. Tens of thousands of micro algal species makes this a potentially rich source of an array of chemical products with applications in food, cosmetic, pharmaceutical and fuel industries. India being a tropical country, with numerous marine micro algal species and optimal conditions for commercial-scale algal production, can effectively utilise these resources for nutraceuticals and biofuel production.

The LTTD plants discharge several hundred-meter cube of deep sea cold water every day as a byproduct after the generation of fresh water. The deep sea cold water pumped from 300 m depth is 3-5 fold rich in nutrient when compared to the surface seawater, which NIOT has taken up a research and development programme towards its utilisation for mass culture of economically important marine micro algae with the following objectives:

  • Isolation and screening of marine micro algae for photoautotrophic production of nutraceuticals and biofuel;
  • Design and development of photobioreactor, solar powered raceways and optimisation of mass culture methods; and,
  • Development and standardisation of harvesting, dewatering, extraction techniques for nutraceuticals and other biochemicals.

Mono species cultures of about a hundred strains of marine micro algae were isolated from the Lakshadweep and were screened for growth, biomass and lipid production.

 

Artificial Reefs

Artificial reefs are man made underwater structures deployed essentially to promote marine life in the featureless bottom of coastal waters, which increases the bottom surface area and provides surfaces for algae and invertebrate settlement. The accumulation of settled marine life on the artificial reefs also provides food for fish assemblage. NIOT has developed three types of artificial reefs in a pilot project undertaken in Odisha. The artificial reef structures tested for mechanical strength, handing stress and stability, proved to be successful in increasing the fish catch. Such reefs are also being conceived to be deployed in the Lakshadweep waters to enhance its fish stock.

 

Endnote

LTTD has significant scope for cost reduction as the technology matures. The process does not face brine disposal problems and the discharged cold water, rich in nutrients, attracts a variety of fish. Also spin offs like air conditioning for land based plants and mariculture are viable options for the future. Moreover, the subsequent demand for sea cage and lobster, FADs, etc. have demonstrated the utilisation of technology development to increase the livelihood opportunities for the islanders.

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