Migratory Pattern, Route & Abundance of Hilsa Shad ( Tenualosa ilisha )

Introduction:

Hilsa is considered as one of the tastiest fish due to its distinctly soft oily texture, mouthwatering flavour and superb mouthfeel. The fish is locally called Macher Raja means the king of fish. During entire life, Hilsa shad (the national fish of Bangladesh) migrates both from sea to freshwater and freshwater to sea to meet the biological demand. Hilsa shad (Tenualosa ilisha) lives in the sea for most of its life, but migrates at least 1,200-1,300 km upstream from estuarine region for spawning purpose and it also found about 250 km distance from coastal region. Tenualosa ilisha (ilish, hilsa, hilsa herring or hilsa shad) is a species of fish in the herring family (Clupeidae), and a popular food fish in South Asia. The fish contributes about 12% of the total fish production and about 1% of GDP in Bangladesh. As this is one of the flagship fish species of Bangladesh, conservation of this species is indeed needed. Therefore, knowledge on migratory pattern and route of this species demand more attention to boost awareness and enhance conservatory practice for them in Bangladesh. The largest yield from the hilsa fishery comes from the deltaic region of the Gangetic system of India and Bangladesh, where it is reported to be more valuable than any other single species of fish. Of the three countries of the upper Bay of Bengal region, where the hilsa forms a commercial fishery, Bangladesh reportedly secures the largest share of the landings with about 150,000 tonnes per annum; in India the annual landings may amount to 27,000 tonnes, and in Burma about 4000-5000 tonnes. These include both inland and marine catches.

Scientific classification:

Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Order: Clupeiformes Family: Clupeidae Subfamily: Alosinae Genus: Tenualosa Species: T. ilisha

Binomial name: Tenualosa ilisha (F. Hamilton, 1822)

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Figure 01: T. ilisha

Short Description and Habitat:

Dorsal spines (total): 0; Dorsal soft rays (total): 18-21; Anal spines: 0; Anal soft rays: 18 - 23. Belly with 30 to 33 scutes. Distinct median notch in upper jaw. Gill rakers fine and numerous, about 100 to 250 on lower part of arch. Fins hyaline.

A dark blotch behind gill opening, followed by a series of small spots along flank in juveniles. Color in life, silver shot with gold and purple. The fish is marine; freshwater; brackish; pelagic-neritic; anadromous; depth range 200 m. Within a tropical range; 34°N - 5°N, 42°E - 97°E in marine and freshwater. It can grow up to 60 cm in length with weights of up to 3 kg. It is found in rivers and estuaries in Bangladesh, India, Pakistan and Burma. Schooling in coastal waters and ascending rivers for as much as 1200 km (usually 50-100 km). Migration though is sometimes restricted by barrages. Hilsa far up the Ganges and other large rivers seem to be permanent river populations. Feeds on plankton, mainly by filtering, but apparently also by grubbing on muddy bottoms. Breeds mainly in rivers during the southwest monsoon (also from January to February to March).

Environment for Hilsa:

Oceanographically, the marine distribution of the species coincides with the Indian monsoon region. In general, this region is characterized by: relatively large continental shelf, monsoon winds, medium to high precipitation and run-off, surface temperature of 20°C-30°C, surface currents changing with the change of monsoons, medium to low organic productivity, presence of sub-surface oxygen minimum layer and relatively low salinity of coastal waters.

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The north-western part of the Bay of Bengal is characterized by a narrow range of temperature variation (24.9°C-29.4°C)and in contrast, by a wide fluctuation in salinity(22.4ppt to 33.4ppt). This is largely due to the reversal of the coastal current and an excess of evaporation over precipitation; maximum values of salinity are observed in May.

Distribution of Hilsa:

Eggs, larvae and juveniles have been found in the upper reaches of the rivers during the southwest monsoon (July to September) and again during the second half of winter (January to February). From October till about the end of November and again during March, juveniles and young ones up to about 8 cm length, are found in the lower reaches and estuarine areas. Young fish of about 15 to 22 cm length occur along the fore shore areas during the winter months (December to February).

While the eggs occur in the sub-surface zones, the juveniles appear to inhabit the surface waters, but later age groups move in deeper zones as well. In the Hooghly, during the winter season, the males have been observed to move in the surface zone and the females in deeper areas.

The normal habitat of the estuarine stocks is the lower regions of the estuaries and the foreshore areas. During the breeding season they ascend the rivers and after spawning, return to the original habitat where they remain till the next breeding season. The riverine stocks appear to remain in the freshwater areas throughout the year but there is a greater concentration in the lower reaches during the period between breeding seasons, thus indicating that one segment of the population is not truly anadromous.

Figure 02: Hilsa Habitat in Bangladesh.

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Migration:

The term migration comes from Latin word “Migrare” which means “to travel.” Generally, migration refers to any movement of animal from one place to another. On the other hand, it can be said that, migration is confined to rhythmic movement of animal which involves a journey from one place to another and come back again. “Generally, a migration is more or less continuous and direct movement from one location to another. Such movement is under the control of the fish, genetically determined, and is influenced by environmental factors. Typically, a migration includes one or more returns to the starting location.”

The upstream migration during the main breeding season appears to depend largely on the commencement of the south-west monsoon and consequent flooding of all the rivers of Bangladesh, Burma and India. The variations in the intensity of the monsoon during the breeding season appear to cause considerable fluctuations of the fish catches in different places. According to Day the minor breeding migration in March-April in the upper way takes place when the rivers are flooded by melting snow, not by monsoon rains.

Hilsa spends a part of its life in the sea not far from the shallow coastal belt. Hilsa continues its ascent throughout the south-west monsoon to nearly the end of the year in the Hooghly. The fish spends the first year of its life in the lower reaches of the rivers and goes to the sea in the third year. The extent of migration in the rivers varies considerably. In the Irrawady, hilsa is known to ascend to a distance of about 724 km from the sea. The range of migration in the Brahmaputra is up to Tezpur, a distance of about 306 km from the Bangladesh border. The stock of hilsa in the river Ganga is reported to migrate as far as Agra and Delhi, covering a distance of about 1287 km.

Figure 03: Hilsa Migration in Bangladesh.

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Reasons behind migration:

Migrations are mainly for spawning or feeding purpose and are generally time oriented. Many factors influence migratory movements. They may be physical, chemical and biological.

a. Physical factors: Bottom materials, water depth, current and tide, turbidity, temperature, and light intensity;

b. Chemical factors: Salinity, alkalinity, dissolved gases, odor, tastes, and pollutants andc. Biological factors: Sexual development, blood pressure, social response, hunger, food,

physiological clock, and endocrine state.

Figure 04: GIS Mapping for Water Quality (Air Temperature) for the Padma and Meghna River System During the Spawning Period

Migratory pattern, route and abundance of Hilsa shad:

Generally, two types of migratory pattern are seen for Hilsa shad in Bangladesh. These are-

a. South-west monsoon migration: During this migration, Hilsa fish mainly lives in the sea and around the monsoon, when consequent flooding of all the rivers and

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it is time to spawn, swims against the tide and goes back to the river where its mother had given birth to it. Earlier, the Hilsa would move from the Bay of Bengal to Bangladesh rivers, the Padma, and the Meghna, for spawning. It would also take the western route to the Ganga. Now there is more hilsa in the west, in areas bordering Indian waters.

b. Winter migration: Migration of Hilsa shad is not limited to monsoon only, but it also migrates short period during winter. It happens during the month of February to March.

Figure 05: Migratory Pattern of Hilsa.

Movement pattern of Tenualosa ilisha/ hilsa into different habitats Hilsa is anadromous in nature with a life cycle that follows the general pattern of breeding upstream in the freshwater and the larvae hatching from the free floating eggs. The immature young stages grow in river channels and then descend to the sea for a period of feeding and growth before returning to the rivers as mature breeding adults to complete the cycle. There are three types of grounds in Bangladesh used by the Hilsa to complete their entire life cycle or migration.

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Spawning grounds:

Adult brood Hilsa mainly spawn in Bangladesh’s major deltaic rivers, estuaries and coastal areas. Hilsa spawn throughout the year but the peak season is September and October. But it has four main spawning grounds in Bangladesh (Halder and Islam, 2008). These are-

i. Dhalerchar of Charfashion in Bhola (about 125 sq. km area);ii. Monpura in Bhola (about 80 sq. km area);

iii. Moulavichar of Hatia in Noakhali (about 120 sq. km area);iv. Kalirchar of Sandwip (about 194 sq. km area) of Bangladesh.

Figure 06: Breeding area of Hilsa in Bangladesh.

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Hilsa spawn more or less throughout the year, they have a minor spawning season during February-March and a major season in September-October. Local fishermen catch migrating adults from February to May from different deltaic rivers.

Nursery grounds:

After hatching from free floating eggs, the larvae remain in their nursery grounds where they feed and grow. There are mainly five nursery grounds where Jatka (Hilsa fish sized less than 25 cm) grows for six to ten weeks before going back to the sea for further growth and maturity. There are five main nursery grounds:

i. A 100-kilometre stretch of the Meghna River from Shatnol, Chandpur District to Char Alexander, Lakshmipur District

ii. 90km of Shahbajpur Channel, a tributary of the Meghna River, from Madanpur/Char Ilisha to Char Pial, Bhola District

iii. 100km of the Tentulia River from Bheduria, Bhola District to Char Rustom, Patuakhali District

iv. 40km of the Andharmanik River route at Kalapara Upazila, Patuakhali District

v. A 20km stretch of the Padma River’s lower basin from Narhira to Bhedarganj, Shariatpur District (DoF 2013).

Four of these were declared hilsa sanctuary areas in 2005 and the fifth in 2011. A mature female hilsa can be between 30 and 55 centimetres long and lays 0.1 to 2 million eggs in fresh water. Hatching takes between about 23 to 26 hours at an average temperature of 23°C (DoF 2008). The newly hatched larvae (about 2.3 millimetres long) make their way downstream to the sea through their freshwater nursery grounds, feeding and growing on the way. At this juvenile stage of their life cycle, a period of five or six months, they are known locally as jatka. They are abundant between February and May in the foreshore and riverine waters of Padma, Meghna and other deltaic rivers in Bangladesh.

Feeding and growing grounds:

Juvenile Hilsa spends about 1-1.5 years in the Bay of Bengal for further growth and development. When these fishes become sexually mature, they begin their journey to the estuary and river for spawning purpose and the cycle continues.

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Figure 07: Migratory Route and Abundance of Hilsa Shad.

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Hilsa Sanctuaries in Bangladesh:

Hilsa sanctuary area Ban period100km stretch of the lower Meghna River from Shatnol, Chandpur

District, to Char Alexander, Laxmipur DistrictMarch to April

90 km stretch of Shahbazpur Channel, tributary of the Meghna River, Char Ilisha to Char Pial, Bhola District

March to April

100km stretch of the Tetulia River from Bheduria, Bhola District to Char Rustam, Patuakhali District

March to April

Whole 40km stretch of the Andharmanik River in Kalapara Upazila, Patuakhali District

November to January

20km stretch of Lower Padilla River, between Naria-Bhedorganj Upazila, Shariatpur District in the north and Matlab Upazila,

Chandpur District and Bhedorganj Upazila, Shariatpur Districtin the south.

March to April

Figure 08: Hilsa sanctuaries in Bangladesh.

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Conclusion:

The migration route and pattern is now clearly known to us. Hilsa, the national fish of Bangladesh, generates employment and income for millions of people in Bangladesh, India and Myanmar. Hilsa also remains a subsistence food for many poor coastal communities. That’s why we must save this resource by stopping to capture this fish during migration periods. To overcome the challenges to the design of the hilsa conservation and economic incentive program, we must identify Hilsa sanctuaries, speeding up the judicial system to resolve cases related to hilsa fishing and increasing awareness among fishers of the long-term benefits of hilsa conservation. To carry out the hilsa conservation and economic incentive program effectively, the Department of Fisheries needs the support of additional human, physical and financial resources. Hilsa is our national fish. That’s why we must give chance to this species to grow up willingly. So, we can enrich with this natural resources and can able to export this fish by fulfilling our countries depend. In the time of implementing rules for Hilsa conservation, knowledge about its migration pattern is must know to all. Now it is clear to us. That help us in future implementation.

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Recommendations:

Ahsanullah, M. 1964 Population dynamics of hilsa in East Pakistan. Agri. Pak., 15(3): 351—365.

Amin, M. R. 1975 The morphology and histology of the alimentary tract of Hilsa i/sha (Ham.) with special reference to food and feeding habits. Thesis work for M.Sc. degree at the Deptt. of Zoology, University of Dacca. (See also Shafi, Quddus and Amin, 1976; Reference obtained from Freshwater Fisheries Research Station, Chandpur, Bangladesh).

Chacko, P. I., S. V. Ganapati and A. R. K. Zobairi 1949 Hydrobiological investigations of the Godavari River with reference to the Indian shad, Hilsa ilisha (Ham.). Proc. Indian Sci. Congr., 35(3): 209.

Chacko, P. I., A. R. K. Zobairi and B. Krishnamurthy 1948 The radii of scales of Hilsailisha (Ham.) as an index of growth and age. Curr. Sci., 17(5): 158-1 59.

Chandra, R. ‘1962 A preliminary account of the distribution and abundance of fish larvae in Hooghly estuary. Indian J. Fish., 9(1) : 48-70.

Chandrasekhar, K. 1961 The structure of the kidney of some teleostean fishes. Proc. Indian

Mus., 59: 479-495. Chaudhuri, B. 1. 1916 Fauna of the Chilka lake. Fish. Part I. Mem. Indian Mus. 5(4): 403-439. *Das, N. N. 1983 Observations on factors affecting the timing of hilsa, Hilsa illsha

(Ham.) Migrations in major rivers (A research proposal). Institute of Animal Resource Ecology. The University of British Columbia, Vancouver, Canada.

David, A. 1954 A preliminary survey of the fish and fisheries of a five mile stretch of the Hooghly River near Barrackpore. Indian J. Fish., 1: 231 -255.

Day, F. 1 873a Report on the Freshwater Fish and Fisheries of India and Burma. Calcutta: pp. 22, 23, 35-36.

Day, F. 1 873b Report on the Sea Fish and Fisher/es of India and Burma. Calcutta: pp. 24, 25 and App. pp. i, xxxi. cxxi & cxxii.

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