Arabian Sea large marine ecosystem
The Arabian Sea Large Marine Ecosystem (LME) is characterized by its tropical climate. It encompasses three sub-regions in the Indian Ocean. The Western Arabian Sea borders Somalia, Yemen and Oman; the Central Arabian Sea borders Iran; the Eastern Arabian Sea borders India and Pakistan. Each sub-region has its own originality in terms of current patterns, physical characteristics, physiochemical qualities, dominant species and biodiversity. There is extensive interchange of surface waters in the Indian Ocean between the Arabian Sea LME and the Somali Current and Bay of Bengal LMEs. A few rivers (Indus, Euphrates and Tigris) empty into the LME. LME book articles and chapters pertaining to this LME include Dwivedi and Choubey, 1998; Bakun et al, 1998; Baars et al, 1998; and Piontkovski, 1998.
The continental shelf is widest off the Northwest coast of India. This region has tropical cyclone storms. There is extensive interchange of surface waters in the Indian Ocean, encompassing the Arabian Sea LME, the Somali Current LME and the Bay of Bengal LME. Depending on monsoon winds, local topography, the width and depth of the continental shelf, and drainage of coastal areas, there are three coastal ecosystems, each characterized by its own productivity and species distribution. For more information on these 3 sub-regions, see Dwivedi and Choubey, 1998. There is a complex set of ecologic processes affecting trophic enrichment, food distribution, and advection of swimming organisms. The Arabian Sea LME is strongly influenced by monsoons. During the southwest monsoon, from May to October, the winds in this region are from the southwest, inducing a great deal of evaporation from the warm waters of the Arabian Sea, and heavy rainfall along the coast of India. The winds blow toward India and cause upwelling of low-oxygen waters. There is a concentration of fish in nearshore areas at that time. During the other half of the year, the winds blow in the opposite direction, and not as strongly. For a map of the southwest and northeast monsoons, see Bakun et al, 1998, pp 120 and 121. For more on surface circulation and on upwelling in the Gulf of Aden, off Oman and off the Southwest Indian coast, see Bakun et al, 1998. For data on monsoons observed in 1992 and 1993, see Baars et al, 1998. There is more information on the Arabian Sea’s geological and climatic evolution, the role of JGOFS in the Arabian Sea, and on Arabian Sea seasonal changes in upwelling and productivity. This tropical region shows great marine biodiversity. The Arabian Sea LME is considered a Class I, highly productive (>300 grams of Carbon per square meter per year (gC/m2-yr)) ecosystem based on SeaWiFS global primary productivity estimates. For more information on productivity in the Gulf of Aden, see Baars et al, 1998. For more information on former Soviet expeditions to the Indian Ocean, conducting field surveys of plankton fields and studying physical, chemical and biologic characteristics, see Piontkovski, 1998. In this LME, there are clear differences in salinity in water masses of different origin. Off of India’s southwest coast, mudbanks help to increase productivity.
The Food and Agriculture Organization (FAO) 10-year trend shows an increase in capture trends, from 1.9 million tons in 1990 to 2.2 million tons in 1999 (see FAO, 2003). This is one of only 6 LMEs identified in which trends are not decreasing, and for which a precautionary approach to management might lead to sustainability. The greater marine biodiversity of this tropical region is reflected in catch composition. There is a high catch percentage for coastal fishes, and for pelagic fishes. Fisheries of large oceanic pelagic fishes are substantial and lucrative (see Bakun et al, 1998). There are catches of herrings, sardines, anchovies and crustaceans. For information on the spiny lobster in the Indian Ocean, and for the distribution of P. homarus megasculptus in relation to surface circulation patterns in this LME, see Pollock, 1998, and the distribution map for January and July, page 218. The catch composition is quite stable for this LME. For biologic production and fishery potential in the EEZ of Western India, see Desai and Bhargava, 1998. India’s southwest coast is fished for oil sardines (Sardinella longiceps), mackerels (Rostrelliger kanagurta), and tunas (Euthynnus affinis and Auxis thazard). Most of this catch comes from a narrow 10-15 kilometer (km) coastal belt, and accounts for 23.6% of India's fish catch (see Ddwivedi and Choubey, 1998). The dominant fish species off India’s central west coast ecosystem are Sciaenids (Pseudosciaena diacanthus), Carangidae (Caranx spp.), and Engraulidae (anchovies). The dominant species off India’s northwest coast are prawn, Sciaenids (Pseudosciaena diacanthus), and Carangidae. Small tuna (Euthynnus affinis) migrate to this area to breed. The University of British Columbia Fisheries Center has detailed fish catch statistics for this LME. A graphical representation of the FAO data is available.
Pollution and Ecosystem Health
Current fishing methods have resulted in the overexploitation of coastal resources such as sardines, prawns, pomfrets and mackerel. However, most of the fish stocks breed in deeper offshore waters so there is an opportunity to rebuild stocks. The overexploitation is mostly due to large fishing vessels that fish illegally near the coast. The market price for these species appears to be the driving factor for this overexploitation. Population expansion especially in India will continue to put pressure on coastal resources. For this reason, there is an urgent need for a long-term plan for the conservation and management of the LME. This population pressure also creates major pollution problems, like untreated organic waste and sewage, which contribute to the nutrient loading of nearshore areas. For more information on sewage, industrial wastes, and oil pollution, see Dwivedi and Choubey, 1998. Nutrient loading influences productivity cycles and depletes dissolved oxygen supplies. Rapid industrialization is also contributing pollution from industrial wastes and industrial effluents. Heavy metals such as cadmium, lead, manganese, and zinc have been found in benthic core samples to depths up to 45 centimeters. Large amounts of pesticides are also deposited in the coastal areas, particularly off the Bombay coast. This situation would require the dredging and removal of contaminated sediments. Oil pollution is also a factor in the Arabian Sea LME. Large quantities of oil are transported through the Arabian Sea’s shipping lanes. Oil from accidents and bilge washings can reach the coast and impact coastal ecosystems.
65% of fish landings derive from artisanal fisheries. Coastal populations have traditionally relied on non-motorized boats (see Dwivedi and Choubey, 1998). Along its Arabian Sea coast, India operates 180,000 country crafts, 26,000 motored traditional vessels, 34,000 mechanized boats, and a few large boats. The most important export is prawn. Overexploitation of prawns, sardines, mackerels and promfrets has been caused by the introduction of large fishing vessels that fish illegally near the coast (see Dwivedi and Choubey, 1998). It is uneconomical to harvest the deep-water fisheries because of low market price. Only tuna commands a good price. Population expansion especially in India will continue to put pressure on coastal resources. India has over one billion people to feed. Seventy percent of its population eats fish. India would require 13 million tons of fish to meet minimum standards, yet present production is only 3.9 million tons, with aquaculture providing an additional 7 million tons. The pressure to feed this population creates a serious threat of overexploitation of this LME’s coastal resources. The Arabian Sea is a major oil route.
Somalia, Yemen, Oman, Iran, Iraq, Kuwait, India and Pakistan share in the governance of this LME. Given the region’s cultural, religious, political and ethnic diversity, its economy and the demands of development, the quest for sustainable development and joint governance of the LME poses problems. There have been wars between several of these countries. India’s population explosion and pollution issues underline the need for an ecosystems approach to conservation and sustainable development. There is urgency in the need for a long-term management plan. The multiplicity of national boundaries and EEZs make governance complex. The coastal nations of the region need to develop a regional framework that would encompass jurisdictional issues.
Articles and LME Volumes
- Baars, M., P. Schalk, and M. Veldhuis, 1998. Seasonal fluctuations in plankton biomass and productivity in the ecosystems of the Somali Current, Gulf of Aden, and Southern Red Sea. In: Kenneth Sherman, E. Okemwa and M. Ntiba. (eds.), Large Marine Ecosystems of the Indian Ocean: Assessment, Sustainability, and Management (Cambridge, MA: Blackwell Science) pp. 143-174. ISBN: 0632043180.
- Bakun, A., C. Roy, and S. Lluch-Cota, 1998. Coastal upwelling and other processes regulating ecosystem productivity and fish production in the western Indian Ocean. In: Kenneth Sherman, E. Okemwa and M. Ntiba. (eds.), Large Marine Ecosystems of the Indian Ocean: Assessment, Sustainability, and Management (Cambridge, MA: Blackwell Science) pp. 103-142. ISBN: 0632043180.
- Desai, B.N. and R.M.S. Bhargava, 1998. Biologic production and fishery potential of the Exclusive Economic Zone of India. In: Kenneth Sherman, E. Okemwa and M. Ntiba. (eds.), Large Marine Ecosystems of the Indian Ocean: Assessment, Sustainability, and Management(Cambridge, MA: Blackwell Science) 297-309. ISBN: 0632043180.
- Dwivedi, S. N. and A.K. Choubey. 1998. "Indian Ocean Large Marine Ecosystems: Need for National and Regional Framework for Conservation and Sustainable Development", in Kenneth Sherman, E. Okemwa and M. Ntiba (eds.), Large Marine Ecosystems of the Indian Ocean: Assessment, Sustainability, and Management (Cambridge, MA: Blackwell Science) pp.327-333. ISBN: 0632043180.
- FAO, 2003. Trends in oceanic captures and clustering of large marine ecosystems—2 studies based on the FAO capture database. FAO fisheries technical paper 435. 71 pages.
- Piontkovski, S.A., 1998. Spatial-temporal structure of Indian Ocean ecosystems: a large-scale approach. In: Kenneth Sherman, E. Okemwa and M. Ntiba. (eds.), Large Marine Ecosystems of the Indian Ocean: Assessment, Sustainability, and Management (Cambridge, MA: Blackwell Science) pp223-233. ISBN: 0632043180.
- Pollock, D., 1998. Spiny lobsters in the Indian Ocean: speciation in relation to oceanographic ecosystems. In: Kenneth Sherman, E. Okemwa and M. Ntiba. (eds.), Large Marine Ecosystems of the Indian Ocean: Assessment, Sustainability, and Management (Cambridge, MA: Blackwell Science) pp. 215-222. ISBN: 0632043180.
- Banse, K., and C.R. McClain, 1986. Winter blooms of phytoplankton in the Arabian Sea as observed by the Coastal Zone Color Scanner. Marine Ecological Progress Series, 34, 201-211.
- Brock, J.C., C.R. McClain, M.E. Luther, and W.W. Hay, 1991. The phytoplankton bloom in the northwest Arabian Sea during the southwest monsoon of 1979. Journal of Geophysical Research, 96, 20,623-20,642.
- Brock, J.C., and C.R. McClain, 1992. Interannual variability in phytoplankton blooms observed in the northwestern Arabian Sea during the southwest monsoon. Journal of Geophysical Research, 97, 733-750.
- Smith, S.L., K. Banse, J.K. Cochran, L.A. Codispoti, H.W. Ducklow, M.E. Luther, D.B. Olson, W.T. Peterson, W.L. Prell, N. Surgi, J.C. Swallow, and K. Wishner, 1991. U.S. JGOFS: Arabian Sea Process Study, U.S. JGOFS Planning Report Number 13, Woods Hole Oceanographic Institution, 164 pp.
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