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Our Fisheries Resources And. the Role of Upwelling in Their Fluctuations

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Our Fisheries Resources And. the Role of Upwelling in Their Fluctuations Our fisheries resources and . the role of upwelling in their fluctuations Part II IMARY PRODUCTIVITY AND FISHERIES POTENTIAL M. KUMARAN Pelagic Fishery Project. Cochin-16 organic matter by higher utilization of the incident light is initiates the whole marine possible only if the phytoplankton is Con­ chain, which terminates in the larger centrated in the upper layers, where light and marine mammals. The prime absorption by water is low. Plant growth "oesiiselrs of organic matter in the .sea occurs \\hereyer photosynthesis exceeds re­ the planktonic algae found in the upper spiration. Therefore , higher rates of produc­ where there is sufficient light penetra­ tion is expected in coastal waters. for photosynthesis. Tberefore. a know­ of tbe standing crop and rate of pro­ Nutrients and primary prcductil'ity of phytoplankton in different regions The availability of essential nutrients in "~g;lIi(lnS on organic production to assess the productive uPFer la yers is one of the Rlative fertility of the sea were being important fact ors governing the magnitude of out during the past two decades. orga nic producti on. The nutrients are 14 experiments on primary produc- brought up into the euphotic zone by tbe vertical mixing of the water cau sed by wind inshore and offshore and wave actio n; processes associated with ocean c~rren\S and by upwelling of deep waters. The general level of nutrieats is bigh important factors infiu­ in the Arabian Sea, especially so in the the amount of euphotic zone, \I hich is a potentially produc­ reaching the surface of the sea. A tive condition. In the Arabian Sea during n.orv, 1978 9 mon'won, the coastal water is enriched by in the Bay of Bengal and in the Andaman S the nutrients brought up from sub.;urface phosphates are almost utilised by the phyt levels. A direct correlation between the plankton. The magnitude of primary pr content of phosphates and ri ch phytoplankton duction is influenced primarily by the ava was ob,ecved during the monsoon months. ability of nutrients as other conditions a The hydrographical conditions during this never limiting. Hence a study of the seaso period seem to be mainly responsible for the variations of nutrients could provide valua rate of replenis hment of nutrients far exceed­ information on the primary productivity. ing their utilization. The precess of replenish­ ment is more intense towards the southern Regional and seasonal variations in part of the west coast of India. During the primary productivity postmonsoon the nutrient levels decreases 57 million hectares of shallow due to theincreasing vertical stability of the contiguous to the coast line of India. T waters. In the offshore regions marked continental shelf of India is much wider· variations in the nutrient levels are observed certain regions en the west coast than on t in different seasons. But in the inshore east coast. There is considerable season regions, the seasonal variations in nutrient and regional va riation in the magnitude concentration is relatively less because ofthe organic production. Some of the m constant mixing of the water. On the south­ productive regions are found on the con· west coast theemaximum production of phyto­ nental slope. plankton takes place during the south· west monsoon. There is another peak of le sser The Arabian Sea is highly productive cause of the presence of regions of deep wat magnitude in the north-east monsoon months ascent. Generally the level of organic pr between December and February. Plankton duction is high near the coast and becom production during the south-west monsoon less seaward. Studies on the primary pr on the west coast surpasses those from some duction in the seas around India have sho of the most fertile coastal regions of the that the shallow areas of the Gulf of Mann world. The nutrient concentrations in the Palk Bay and Wadge Bank are extreme Bay of Bengal is of a lower order compared productive, with an average rate to the Arabian Sea. The absence of large 2.0 gC/m'/day during most of the year a scale upwelling is presumably responsible for with the highest values of over 6.0 gC/m"/da the lower level of nutrients and phytoplank­ These high rates are almost equal to tho ton concentration here. found in some of the worlds most producti waters as in the regions of the Somali coast. A direct correlation exists between pri­ mary production and nutrient concentration - In the shelf waters of India, the avera low values of primary production coincided gross production comes to 1.19 gC/m"/da with the deficiency of nutrients. In the which amounts to an annual gross producti central part of the Arabian Sea and in the of 434 gC/m'/day. Assuming that 40% open ocean nitrates are practically absent and this is being utilized for respiration, the n 10 Seafood Export Journ uction would amount to 260 gC/m'/year. rents. The migration of these organisms or the zone between 50 m depth and the the animals that feed on them can sustain of the continental shelf, the average large stocks of pelagic li>hes in the open is 0.43 gC/m'/day which is moderately ocean where the apparent organic production In this region the annual gross pro­ is of a lower order. Hence large shoals of of carbon would amount to 157 pelagic fishes could sustain in the open parts •.__ .~ /year and the net production 94 gCfm'f of the Arabian Sea in vi ew of the high The net production on the western productivity in certain re gions. Generally, has been estimated at 46 x 10' tonnes the trend ~nd magnituJe uf production arc year, which is about 3 times that of the reflected in the fishery potential of the regions production on the shelf regions of the concerned. coast. Observations carried out on the In the Ba y of Bengal, the areas of highest ...- .. coast have clearly indicated a gradual phytoplankton concentration were near the in the rate of production from shore on the northern and eastern regions "olIow waters to the deeper regions of the where there was replenishment of nutrients to and slope. Beyond the shelf the level of a crrtain extent due to upwelling. The "pnic production falls to < 0.2 gCfm'/day. a verage value of 0.63 gC/n.'/day found in the _Bhc:r rates of production are found near Bay of Bengal is moderately high. However, Laccadive and Minicoy Islands. Certain it is only about one half of tbe productivity !":ciClDS of Arabian Sea is highly productive of the west coast within 50 m depth and account of the presence of unusually high slightly more than the average value for the of organic nutrients at shallow depths region outside the shelf. The total net within or in close proximity to the production over the shelf amounts to 15 x 10· zone. When these nutrient s are tonnes. T hus it could be seen that the west ~1JU1!ht to the euphotic zone a high level of coast of India \',"ith a wider continental shelf Fim.,ry production could be sustained. The and a more pronounced upwelling accounts ...soon shift provides the required energy for three· months and the east coast one· the vertical mixing of the water column fourth of the entire net primary production. brings appreciable quantities of nutri­ This disparity is reflected in the magnitude of to the surface layers. High concentration the fisheries resources along these coasts. phosphates (3.73 ug. at/ I) during May­ have been observed in the eastern Standing crop of plankton .an:tan Sea between 0 and 200 metres. In The Arabia n Sea has been found to be ...,'esltern Arabian Sea also high concentra­ the richest part of the Indian Ocean in plank­ of phosphate (>2.0 ug. at/l) have been ton production. This goes to sustain the at depths of 100-500 metres. The pelagic fisheries of oil sardine, mackerel and ri ch water from the intermediate several olhers, high seas fishery and the de­ when brought up to the surface sup­ mersal fisheries on the sbelf chiefly prawns a heavy growth of planktonic organisms which feed on the organic matter at the spread seaward with the surface cur- bottom. The presence of upwelled waters ft!l],ruB'rv 1978 11 7'ot OVtlt 4 7 'ftltl.t~ B U I L D IN GIN T ERN A T ION A L UN D E R S TAN DIN G through INTERNATIONAL TRADE We are one of the pioneers in the INDIAN FROZEN SEAFOOD TRADE We are specialists in INDIAN FROZEN SEAFOOD We want to do business with you Exclusively represented in India by our buying agents: J M M Enterprises c/o Shapoorji Pallonji & Co. Gresham House, 4th Floor, Sir P. Metha Road, BOMBAY 400001, India. ARISTA INDUSTRIES, INC. 500 Summer Street, Stamford, CT 06901 u. s. A. Telephone: (203) 327 - 2393 Cable Address : HACKBEN, Stamford, Conn. Telex: 996493 18 Seafood Export JOUTlI - along the coast between Cape Comorin to order during the south·west monsoon season. Karwar is responsible for the high nutrient several times the magnitude of that during the content of the west coast. It may be seen north-east monsoon season. The zooplankton that the standing crop of pbytoplankton is of crop does not show such sharp oscillation a high order throughout, but during the because their peak development succeeds that lOuth-west monsoon period it attains the of the primary producers. the phytoplankters peak of development. The fan in tbe stand­ and are probably being eaten up or carried ing crop of phytoplankton during the north­ away by the prevailing currents to distant east monsoon season is partly due to the places.
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