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Indus delta mangrove ecosystem



Science & Technology


Politics & Policy

Fishery and marine biology aspects

By Dr. Iqbal Panhwar
Director General University Grants Commission
 Apr 30 - May 06, 2001

The Indus delta stretches over an area of 600,000 hectares between Karachi and south-western border of India. It is a typical fan shaped delta built up by discharge of large quantities of silt washed down from the Karakoram and Himalayan mountain ranges by the river Indus. It houses the World's largest arid climate mangrove ecosystem consisting of seventeen major creeks and extensive mud flats, sand dunes, salt marshes and mangroves(l58,500 ha). The Indus delta mangroves are perhaps unique in being the largest area of arid climate mangroves in the world. An estimated 135,000 people are depending on the resources of this ecosystem for their livelihood, and it supports a variety of lives. This mangrove vegetation is characterised by a woody formation consisting of Avicennia marina, Ceriops tagal and Aegiceras corniculatum. Avicennia marina is dominant and occurs as an almost monotypic stand throughout the area.

Under the federal government's core-umbrella project EPRC (Environmental Protection and Resource Conservation), the sub project Rehabilitation and Replanting of the Indus Delta Mangroves(RRIDM) was funded by the World Bank and the GoS .It was implemented by the Coastal Forest Division of the Sindh Forest Department. A rapid diagnostic study of the Indus delta mangrove ecosystem was made on the basis of available literature, field studies, interviews with villagers and key informants. The present report focuses the fishery aspects of this ecosystem based on synthesis of existing data, literature and the present state of fishery operating in the inshore and offshore waters of Sindh; the research work done under the RRIDM project and also the areas for future research in order to understand the structure and dynamics of this very special ecosystem.

The main communities living on the fringes of the creeks or within the ecosystem are the Mir Bahar and the Jats. An estimate of total population of the coastal communities being dependent on the resources of the ecosystem was made by the RRIDM project figured at 135,000 of which 72% live in the urbanised Port Qasim sub-system. Natural resources of this ecosystem are harvested by the local communities for a variety of purposes, such as fishing, camel browsing, buffalo grazing and fuel wood collection etc. Fishing is the principal sector in terms of economic value (98%).

Most of Pakistan's commercial marine fishery operates on the coast of Sindh, where fishing occurs within the mangrove creeks and in the neritic waters off the mouths of creeks. The marine fishery of Pakistan relies greatly on shrimps, being the most important of all the categories in terms of value of landing. This lucrative foreign exchange earning commodity highly influenced the development of fishing crafts and gears in the country especially along the coast of Sindh, and this development during the past three decades was predominantly aimed as catching more and more shrimp stocks. It was estimated (in 1997) that the value of shrimp caught at the coastal waters of Sindh was around Rs 2,834 million, while the value of mangrove dependent /loving finfish during the same year was Rs 780 million. Export value of shrimps was around US $ 100 million (= about 97% of Pakistan's total shrimp export value). Besides these, export of Khunka (mud crab) scylla serrata contributed about Rs 120 million (= US $ 3 million) to the export earnings in 1997. Following the world wide demand of fishery products fishing activities expanded and intensified with modernization of the fishing fleet during the last two decades. Local communities got attracted to fishing and now most villagers derive bulk of their income from fishing, trade and processing.

In order to delineate the importance of mangroves to the rich marine fishery of the Indus delta it will be better for us to first review some important oceanographic features of the shelf sea of Pakistan. The northern Arabian Sea is believed to have high productivity and this consideration leads to the optimism that the off shore marine fishery resources of Pakistan may of considerable magnitude. However, there are certain hydrographic features in off shore waters which does not seem to encourage large fishery production, at least affect it in a negative way. For instances the continental shelf of Balochistan is narrow (13-32 km wide), anoxic conditions resulting in mortality of fish and shrimps or their migrations are also known to occur. In the Arabian Sea, everywhere north of 200 N, a layer of extremely low oxygen concentration (<Iml/l) extends from above 200m down to more than 1200m depth.

During SW monsoon season, up sloping of oxygen deficient subsurface water occurs. At times water with low D.O. content(l.7 ml/l) is found even at a depth about of 15 m. Banse pointed out that low oxygen values near the bottom of the continental shelf between Bombay and Karachi would some times affect the distribution of benthic animals, demersal fish and shrimp. In his another contribution, he mentioned that fish and shrimp on Pakistani shelf would be less affected than on the west coast of India, since D.O. values on Pakistani shelf are relatively higher. He also pointed out that the conventional upwellings do not occur along the coast of Pakistan; instead up-sloping of cool, oxygen-deficient and nutrient-rich water occur, and the shallow thermocline keeps nutrients down.

There are still other factors which may now favour large fishery production in the Arabian Sea off the coast of Pakistan. For instance, the prevailing high salinities(36.2 - 36.5 %) in the northern most part of the Arabian Sea; the creeks and back waters have become hyper saline; the RRIDM survey records about 37-42 % in the Karachi range. The confluences of the river lndus lost their estuarine character in the souths-western part of the delta as a result of up stream withdrawal of sweet water by barrages. Thus, the question arises that, why the marine fishery resources of the Indus delta is so rich?

Fortunately, the inshore and neritic waters of Pakistan where the present marine fishing fleet operates are shallow and productive, probably being influenced by mangroves in the vicinity. The following discussion will make it more clear.

Mangrove loving shrimps and finfishes reported elsewhere are also very common here (in commercial catches) e.g., penaeid species of the genera Penaeus (JAIRA) Metapenaeus (KALRI), Parapenaeopsis (KIDDI), and the major groups of finfishes e.g., mullets, grunters, croakers, shads, groupers, snappers, cat fishes, cat fish eels, anchovies, pomfrets, trevallies, barracudas, threadfins and therapons etc. The importance of mangroves to the rich marine fishery of Sindh may be deduced from a comparison of the marine fish catch statistics of the two coastal provinces of Pakistan alongwith their mangrove covers and the coast line lengths. For instance, althoug Sindh has about half the coast line length (330 km) of that of Balochistan (645 km), but it has a great wealth of mangroves (158,500 ha), about 22 times larger than that of Balochistan (7,340 ha). The annual average catch of shrimp (most valuable item) from Sindh coastal waters is 27,584 tons, being about 35 times larger than that of Balochistan (795 tons). Expressed on the basis of per kilometre coast line length only about 1 ton/km is harvested in Balochistan against 84 tons/km in Sindh. Similarly annual finfish harvest in the coastal waters of Sindh (X = 231,242 tons) dominates over that of Balochistan (X = 103,512 tons) by a great margin. Expressed on the basis of per kilometre coastline, the catch in Sindh is nearly 5 times higher (664 tons/km) than that of Balochistan (134 tons/km). Therefore, the underlying cause of this elevated productivity in the coastal waters of Sindh is nothing but its wealth of extensive mangroves. This direct relationship is sharper in case of shrimp. Likewise the relationship of mangroves with rich fishery productivity in the coastal and offshore waters of neighbouring and other countries has been also reported by several authors. Thus, it will be better for us to say 'manage and rehabilitate mangroves to sustain the marine fishery of Pakistan.' A relatively new mangrove based intense fishing activity is catching holding/fattening and exportation of live mud crab Scylla serrata, locally known as Khunka. Export of this item has been increasing over the past years, e.g., 12 tons in 1991 to about 2,922 tons in 1997. This increase is the result of establishment of large commercial farms in Keti Bundar sub system. The stocks are obtained from local fishermen who collect them from mangrove areas.

Besides the tangible products, the Indus delta mangroves protect the coastal villages from tidal and wave actions especially during monsoon season, also it is claimed that the mangroves of the Port Qasim area along the creeks have resulted in a much-reduced dredging cost. Different species of shell and finfishes use this mangrove ecosystem as feeding, breeding and nursery ground. It also provides an excellent habitat for snakes, birds and mammals. Migratory birds find shelter here during winter. Some of the most common animals cited by villagers include pelicans, flamingos, kites, herons, egrets, jackals and dolphins.

As mentioned earlier, on the economic value stand point, the principal beneficiary of the Indus delta mangrove ecosystem is undoubtedly is its fishery (98%) operating within the net work of creeks and tidal channels fringed with mangroves, and the neritic waters; but at present it faces the problem of degradation. So far this degeneration mainly manifests itself through rare occurrence of certain economically important species and therefore, reduced catches of such species. During our field trips to different coastal areas of the delta we came to learn through interviews with the local fishermen that the tiger shrimp Penaeus monodon, Palla Tenualosa ilisha and Dangri Lates calcarifer etc. have become rare now in south-western part of the delta. In this line of observation he also recorded low species diversity in the creeks near Karachi i.e. the south-western region of the delta as compared to less saline creeks near the Indus river and the south-eastern section of the delta Kharochan, Hajamro, Tursian and Bhuri creek). The following causes were identified for degeneration of fish resources:

  • Overfilshing

  • Non judicious fishing techniques

  • Reduction in sweet water flow through the Indus

  • Pollution and changes in hydrography

  • Degeneration of mangrove vegetation and habitat.

Humans played the role of only consumer in this ecosystem, and in the recent past till now the ever increasing population harvests the renewable resources at a pace greater than the natural turnover or replacement rate. Thus, the managers (forest and fishery) must intervene to direct the user groups towards the practice of 'conservation and rational utilisation' of the resources in order to have a sustainable output in future.

To tackle / minimise the effect of stressive factors on marine fishery of the Indus delta the following measures may be considered:

  • Rational harvest of fish stocks in waters both inside and outside the mangrove area,
  • Implementation of legislative control on use of destructive fishing gears, time and space,

  • Diversion of the fisher folk to other income generating activities,
  • Control or minimisation of pollution in the different water areas of the delta,
  • Introduction of EIA before implementation of any development plan,

  • Reduction of post-harvest losses,

  • Rehabilitation, planting and management of mangroves.

Taking advantage of a small financial assistance from the RRIDM project the Marine Reference Collection and Resource Centre (MRC), University of Karachi in collaboration with the Coastal Forest Division, Forest Department, Sindh has given a big step to initiate research works on Marine Biological aspects with emphasis on Fisheries Oceanography. An inventory of economically important shell and finfishes found in catches of fishermen in different area of the Indus delta mangrove ecosystem has been made which reveals presence of all the major groups of mangrove loving fishes reported elsewhere. Record of physiochemical parameters reveals a great variation especially for salinity in different areas of the delta, probably a manifestation of erratic discharges of sweet water during monsoon, e.g., those recorded for Shah Bundar and Keti Bundar ranges. Analysed net plankton, and nekton samples collected from catches of small meshed destructive fishing gears (Boola) found being operated throughout the coast of Sindh, indicate presence of egg, larvae,: juveniles and adolescents of many economically important shell and finfishes to underline the importance of the Indus delta mangrove ecosystem as an ideal habitat of fishery and other resources.

At one stage field investigation and research work on Marine Biology aspect under this project became about to be extinguished (during July-September,1998), but fortunately after arrival of present DFO(of the Coastal Forest Division/Project Manager) support for the purpose was resumed and now this programme terminates with the following achievements:

  • Results of research work as mentioned above,

  • Publishable materials: A trilingual (text in English with translations in Urdu and Sindhi) booklet on economically important fish resources of the Indus delta mangrove ecosystem, trilingual posters drawing attention for conservation and management of mangroves as well as the fishery resources for having sustainable production out puts.

  • Participation in national/departmental seminars,
    on AQUATIC BIODIVERSITY OF PAKISTAN, 20-22 March,1999, organised by the Marine Reference Collection and Resource Centre, and the Department of Zoology, University of Karachi,
    on The Indus delta mangrove ecosystem: FISHERY ASPECTS, 24th March, 1999, organised by the Centre of Excellence in Marine Biology, University of Karachi and,
    on MANGROVE ECOSYSTEM DYNAMICS OF THE INDUS DELTA, May 1999, organised by the Forest and Wildlife Department, Government of Sindh and The World Bank at the National Institute of Oceanography campus, Karachi, to review the results of research works and the lessons learned, thereby to share the knowledge and drawing attention of the intelligentsia to the importance of the Indus delta mangrove ecosystem for a sustaining marine fishery of Pakistan.

  • Besides, initiation of basic research, a young scientist of MRC, University of Karachi has been trained (on practical aspects) in field investigation as well as laboratory work and analytical procedures as regards hydrobiology of the mangrove ecosystem also on fishery aspects.

The research work done as mentioned above on marine biology aspect under the RRIDM project should be considered as a preliminary case study on the subject which can be treated as an example of a modest beginning for planning further organised integrated multidisciplinary research work in future to learn the role of physical and chemical parameters, and microbial activity on productivity of the Indus delta mangrove ecosystem with emphasis on the following:

  • fresh water drainage patterns

  • soil characteristics

  • climate and weather patterns

  • hydrological characteristics (oceanography) of the creeks, including the pollution aspects

  • flora and faunal productivity

  • the degree and dependence of the fauna on this mangrove environment, and

  • the microbial activity

  • Research on fishery aspect should consider the following:

  • analyses of plankton and nekton of the different habitat zones of the Indus delta mangrove ecosystem, e.g. mangrove creeks and inlets, mud flats, near and far inshore areas; and their role on life cycle,

  • catch analyses of the interacting and destructive fisheries (artisanal and industrial) and their contribution to mortality.

Marine biological research is an essential component for development of an integrated management plan for the Indus delta mangrove ecosystem. However, such research programme is beyond the scope of the Forest Department and therefore, may be best handled by the Marine Fisheries Department in collaboration with the Marine Reference Collection and Resource Centre, other departments of the University of Karachi and the National Institute of Oceanography etc. under a separate project and budget allocation.

As illustrated earlier and having learned the lessons that mangroves are the principal hidden causative factor for higher fishery productivity in the coastal waters of Sindh. Unfortunately the mangrove vegetation cover of the Indus delta faces the problem of degeneration, it decreased from 263,000 ha in 1977 to about 160,000 ha in 1991. In this connection several man-made causes have been identified including camel browsing, fodder collection, fuel wood collection etc. The fishery resources are also facing the problem of degeneration as a result of environmental degradation as well as for a heavy-irrational exploitation pressure. Thus, the conservation strategy objective should not only include management of mangrove plant resources but also regulation of the present virtually uncontrolled fishery as well, operating in the different habitat zones of this ecosystem in order to have a sustainable production output in future. The management body should include government organelles (Forest and Fishery Departments), community leaders regulating fishing, representatives of the fisher folk, fishing industry and research organizations.