Primary productivity studies in the EEZ of Arabian Sea, Bay of Bengal and Andaman Sea during different seasons indicated that the average surface primary production and chlorophyll-a values were high in Arabian Sea [17.08 mg C m3 d 1 and 0.64 mg m3] in Bay of Bengal [14.51 mg C m3 d 1 and 0.33 mg m3].

Secondary productivity studies conducted in the Indian EEZ showed maximum variations in the biomass of the zooplankton in the mixed layer depth. During northeast monsoon, along the west coast the average biomass during day time was nearly double that recorded during night. The East coast and Andaman Sea showed lower biomass during southwest monsoon and high biomass during northeast monsoon with typical night abundance. There was marked increase of mesozooplankton [nearly ten fold] in night collections during southwest monsoon in the Arabian Sea. In general highest biomass for the entire area studied was observed during southwest monsoon along west coast. There was appreciable difference in the standing stock between day [average 255.5 ml/1000 m3] and night [average 1862.5 ml/1000m3].

3.1.2 Fisheries resource survey along the Indian Continental slope

The continental slope area (200 to 1000m depth) of the east and west coasts were surveyed for demersal fish resources through dedicated cruises of FORV Sagar Sampada. Good catches of the deep sea prawn Heterocarpus gibbosus were obtained in the High Speed Demersal Trawl [HSDT] – crustacean version – off Ponnani at 320 depth in April. Other deep-sea species namely Aristius doochl, Triochiurus auriga, cusk-eels, Chloropthalmus sp., Priacanthus sp., Centrolopus sp., spider crabs, etc., were also recorded in the catches.

Bottom trawling operations at depths 300-900 m along the slope area of the Bay of Bengal showed the availability of commercially exploitable stocks of the deep-sea prawns at 820-850 m depth. Demersal surveys in the 200 – 400 m depth zone along the Andaman & Nicobar slope yielded a catch per unit effort of 256 kg/hr, in which Cubiceps was the dominant species. Four new grounds suitable for bottom trawling were identified in this area off 400 m depth.

3.1.3 Studies on the Deep Scattering Layer (DSL)

The DSL realms of the ocean have a rich assemblage of planktons and nektons, which form important constituents of the marine food web.

DSL samples were collected from 39 stations along the west coast covering the pre-monsoon and the southwest monsoon periods. The thickness of DSL layer varied from 20 to 100 m during the pre-monsoon and between 10 and 260 m during the southwest monsoon period. An unique observations of appearance of a 60 m thick layer below 350 m during night at 6deg 40' N and 77deg 30' E was made, implying the lack of vertical migration of this layer, characteristic of the DSL in general. DSL biomass for the west coast varied between 0.17 gm/1000 m3 and 30.53 gm/1000 m3. Though the pelagic shrimps and myctophids appear the dominant groups, other mesopelagics like gonostomatidae, sternophthycidae, astronesthidae, stomlidae, chaullodontidae, etc., made significant contribution to the species composition of the DSL nektons.

Along the east coast DSL samples were collected from 20 stations between 10deg - 20deg N and 80deg - 87deg E and from 17 stations between 10deg - 14deg N and 90o - 94deg E during the southwest monsoon period. DSL was found between 40 and 400 m depth. The dominant groups were pelagic shrimps, myctophids, leptocephalus, crabs, cephalopods, euphasids and siphonophores.

3.1.4 Studies on the toxic algal blooms in the Indian EEZ

Water samples collected from 151 stations in the Indian EEZ were analysed for the presence of toxic algae. In the Bay of Bengal, 2 blooms of Trichodesmium sp., were detected in June 2000, of which the first are extended up to an area of 250 m and the second one spread over an area of 1.5 km. In March 2000, in the Arabian Sea as blooms of Noctiluca sp. were recorded.

3.1.5 Benthic productivity studies

It is believed that there is a direct correlation between benthic productivity and demersal fishery. Assuming a life span of one year for most of the macrobenthos and about 3 months for the meiobenthos, the benthic productivity from an area of 2,51,631.36 sq.km. of the west coast is estimated to be around 3.6 million tonnes. The standing stock of benthos was found to be 28,916.7 kg/km2/yr in 30 m depth, 17,127 kg/km2/yr in 50 m depth, 8260.8 kg/km2/yr in 100 m depth and 5090.5 kg/km2/yr in 200 m depth. This indicates rapid decline in benthic biomass with increase in depth. The samples collected from the east coast through 2 dedicated cruises of Sagar Sampada are being analysed.

3.1.6 Harvest technology and catch composition of deep-sea fishery resources

Studies were carried out under this project with trawls namely High Speed Demersal Trawl-II (Fish and Crustacean version), 51 m long wing semi-pelagic trawl and 33.7 m mega mesh trawl designed by the Central Institute of Fishery Technology (CIFT).

Target specific 51 m long-wing semi-pelagic trawl developed for optimum exploitation of off-bottom resources was tested onboard FORV Sagar Sampada in combination with 1.5 tonnes V form Otter-board and 50.0 m double bridles in the depth range of 43.0 to 68.0 m. A total yield of 3.85 tonnes was obtained from the 24 hauls. The average and the maximum catch per unit effort amounted to 132.0 kg and 151.0 kg, respectively.

The semi-pelagic species consisting mainly of Tachysurus sp., Sphyrena sp., Trichiurus sp. Protonibea dicanthus, Rstrelliger kanaguria, Megalaspis cordyia, Psueudocaranx dentex, Nemipterus japonicus, Scomberomorus sp., Chirocentrus sp., cuttle fish and the miscellaneous fish constituted over 85% of the total catch, establishing the target specific gear in landing of benthic fishery resources.

HSDT II (fish version) was found to be very efficient in landing bottom resources mainly fishes. There was an isolated observation of 1.6 tonnes of Priacanthus hamrur at Lat. 20o 10' 836" N Long. 70o 22' 70" E. It also landed 2.2 tonnes of Odonus Niger along the south west coast of India [Plate-7]. During one of the cruises along the east coast, it landed a rare species of shark viz. Echinorhincus brucus weighing a total of 320 kg from a depth of 260 m.

HSDT II (Crustacean version) landed mainly crustaceans. This gear landed a species of lobster viz. Nephrophis stewartii, considered to be very rare in the Indian waters.