APPENDIX IV.3: THE INDIAN SHARK INDUSTRY (by R.A.M. VARMA)

1 RESOURCES

India is rich in natural resources. Its surrounding seas, the Arabian Sea to the west, the Bay of Bengal on the east and the Indian Ocean to the south, abound in a wide range of commercially important fishes and other marine animals. With a coastline of about 7 000 km and 2.02 million square kilometres of water in the exclusive economic zone [EEZ], the annual harvestable fishery potential of the country is estimated to be 3.48 million tonnes. The present level of exploitation of the resources is about one third of the potential.

On the basis of the available landing figures compiled by the Central Marine Fisheries Research Institute, the Fishery Survey of India and commercial fishing results, potential resource data is shown in Table 1.

Table 1 Marine fish resource potential of India’s EEZ (1 000 tonnes)

The annual production of elasmobranchs in India is around 70 000 tonnes, over 4% of total marine fish landings. Sharks account for between 60 and 70% of this. Tamil Nadu, Gujarat, Maharashtra, Kerala Karnataka and Andra Pradesh supply around 85% of the shark landings in India. Sixty-five species of shark have been sighted in Indian waters and over 20 of these, of the Carcharhinidae and Sphyrnidae families, contribute to the fishery.

Sharks are of great commercial importance the world over, apart from being a significant link in the marine ecology. In India the present annual shark production is around 45 500 tonnes, obtained as a by-catch from a variety of gears. Despite the commercial importance, no serious attempts have so far been made at any targeted exploitation of this valuable resource. Information on the composition of the species of shark landings is very scarce apart from the gross catch statistics.

There are several types of gear that take sharks as incidental catch; the most important among them are trawl net and gill net. There is no detailed information on the landings of sharks by gear type but data available on shark production by mechanized boats at major fishing centres show that trawl nets account for 60% of the shark landings and gill nets account for 38%. Purse seine in Cochin and Mangalore and hook-and-line in Cochin and Bombay take a very small fraction of the catch.

New Ferry Wharf and Sassoon Docks in Bombay, Pudumanai Kuppam in Andhra Pradesh, Tuticorin in Tamil Nadu and Veraval in Gujarat are centres of good landings by trawl net and gill net. Shakthikulangara and Cochin in Kerala are centres for gill net landings.

2 SPECIES AND BIOLOGY OF INDIAN SHARKS

Sharks of the family Carcharhinidae are the most important group, dominating the fishery all over the world, and this applies equally in India. The following species are commonly reported on the Indian coasts.

2.1 Carcharhinus limbatus

This shark is cosmopolitan in distribution in the inshore regions of tropical waters. It is capable of tolerating reduced salinity but never penetrates into fresh water. Its main diet is fish such as sardine, mackerel, croaker and sole with cephalopods and crustaceans. It grows to a maximum size of 2.5m. Males mature at 140-150 cm and females at 150-160 cm. They produce an average of 6 embryos per litter and the size at birth is 55-60 cm. They are usually caught by gill net, hook-and-line or bottom-set net.

2.2 Carcharhinus sorrah

This shark often frequents coral reefs. It is short and sturdy and grows to about 1.5m. It feeds on bony fish such as mackerel and sardine plus squid and prawns. Males mature at 115 cm and females at 120 cm. Litter size is 2-6 delivered between March and May on the Indian coast. The size at birth is 40 cm

2.3 Carcharhinus dussumieri

A small, common species of shark in inshore waters, often confused with another closely resembling species, c.sealei. It feeds on small fish, squid and crustaceans. It grows up to 1m; males maturing at 65 cm and females at 76 cm. Size at birth is 35 cm. It breeds throughout the year and has a litter of two embryos.

2.4 Carcharhinus melanopterus

This Indo-pacific tropical shark is capable of migrating into estuaries and brackish waters for the purpose of delivering its pups. It can grow up to 2.5m. The umbilical scar is visible on young ones immediately after delivery. They are 45-50 cm at birth. Its feed includes fish such as mullet, silver bellies, anchovies, hilsa, skate, prawns and squilla. It is commonly caught by drift gill net and long line.

2.5 Carcharhinus macloti

A small shark which grows to a little over 1m in length. It is caught by gill net or hook-and-line and marketed fresh and salt-dried. Its diet consists of small fish, crustaceans and squid. Males mature at 60 cm and females at 70 cm producing 2 young ones per litter which measure up to 35 cm.

2.6 Galeocerdo cuvier

The largest shark of this type recorded measured 7.4m. A widely distributed tropical shark, it is capable of cruising in mid ocean and shows nocturnal movement into bays and estuaries. Its food includes a wide variety of marine and terrestrial life. Fish such as eels, catfish, parrot fish, flat fish, flat heads, flying fish, porcupine fish, puffers, skates and rays are taken. Marine reptiles eaten are sea turtles, green logger heads and Ridley turtles. Sea snakes, sea birds, sea lions, seals and dolphins are also eaten. This shark, known as the tiger shark, is very dangerous and attacks divers, swimmers and fishing boats. It has the worst reputation as a man-eater. Development is ovoviviparous, the litter size is very large, between 10 and 82, and size at birth is 50-75 cm. Pupping is reported to be between November and January.

2.7 Scoliodon laticaudus

This shark abounds on the west and south coasts of India. The majority of males grow to 50-55 cm and females to 65 cm. The species is mainly caught by trawling. Those caught in drift gill nets are females measuring over 50 cm. Males and females mature at 30 cm and 35 cm respectively. Development is viviparous with yolk-sac placenta. Breeding takes place throughout the year and produces up to 20 embryos per litter. Size at birth is 14.5 cm. It feeds on small fish, crustaceans and squid.

2.8 Rhizoprionodon acutus

A medium sized shark in the shore regions which grows to a little over 1m. It is abundant on the west coast of India from September to February and on the east coast during the summer months. It feeds on all small fish, squid, cuttlefish, crab and shrimp. Development is viviparous with yolk-sac placenta. There are 2-6 embryos per litter which are 26-27 cm long.

2.9 Sphyrna lewini

This is the most common hammerhead shark inhabiting the Indian seas. The species is highly migratory in nature. It feeds on fish such as sardine, anchovies, mackerel, eel, milk fish and sole. Even sharks and rays are eaten. Development is viviparous with yolk-sac placenta and a litter of 15-30 embryos. The size at birth is 45-55 cm and it can grow up to 4.2 ms.

The other major species contributing to Indian fisheries are Rhizoprionodon oligolinx, Isurus oxyrinchus, Sphyrna blochii, Sphyrna mokarran, Rhynchobatus djiddensis, Rhinobatos granulatus, Rhina ancyclostoma, Dasyatis sephen, Dasyatis uarnak, Dasyatis imbricatus, Dasyatis marginatus, Himantura alcockii, Aetobatus narinari, Aetomylaeus niehofii, Aetomylaeus maculatus, Rhinoptera javanica, Gymnura poecilura and Mobula diabola.

Whale shark and cat shark also appear occasionally.

Work on the biology of Indian sharks is very insignificant and this is probably because of the difficulty in getting adequate samples. As there is no regular fishery for sharks, their availability is only incidental. The unwieldy size of many species may also be a contributory factor in this regard. More than one hundred works on elasmobranchs have been published in India but only two or three deal with their age and growth. The rest are mainly faunal and taxonomic studies with just some isolated biological details of a few species.

Since whatever is obtained as bycatch is a multi-species catch of sharks in a multi-gear fishery, no serious effort has been made to assess the catch composition or estimates of landings by species on an all-India basis. Given also the inadequate information on the biology of the species, especially its growth characteristics, these factors explain the lack of attempt to study population dynamics.

3 SHARK PRODUCTS AND PREPARATION TECHNIQUES

3.1 Shark meat for human consumption

Small species of sharks are used for preparing shark meat. The fish is not filleted and the preparation is limited to removal of guts, fins, skin and head.

Equipment

• Cutting board made of hard wood

• Large, broad-bladed and straight-edged knife

• ‘S’ hook secured to the edge of the cutting board

• A pair of pliers

Procedure

• Wash the fish in fresh running water to remove slime and dirt.

• Place the fish on the cutting board and cut open the belly.

• Cut across the throat in front of the pectoral fin girdle and remove the viscera from the belly.

• Cut open along the mid-ventral line to beyond the pelvic fins.

• Turn the fish over and cut off the dorsal fins and tail.

• Skinning: firmly fix the head on the ‘S’ hook with the dorsal surface up, firmly grip the belly flap and the base of the pectoral fins and pull back towards the tail until the skin comes off completely.

• Remove the fish from the hook. Cut from the dorsal surface behind the gills and remove the head.

• The end product thus obtained is shark meat which is washed thoroughly and packed either fresh or frozen according to the requirements of the customer.

This technique is not applicable in the case of large sharks as their bodies have first to be cut into manageable pieces before peeling the skin. Usually the meat is packed, fresh or frozen, as chunks.

3.2 Shark hide for the tanning industry

A special feature of shark is the surface of the skin known as ‘shagreen’ which is a rough leather with dermal denticles embedded in the skin, used for rasping and polishing. A rare and expensive product known as Boroso leather can be obtained by polishing the denticles to a high gloss. The hide can also be converted into a fancy leather by removing the dermal denticles. This leather can be used for shoes and other value-added products such as wallets, dress belts, hand-bags and purses. Skins can generally be produced from sharks without damaged skin, which exceed 1.5m in length. The operation of skinning and salting must not take more than 24 hours. Sharks meant for skinning should not be gutted, iced or frozen beforehand. Fresh water will spoil the skin so only seawater should be used for washing.

Procedure

1. Skinning or flaying

Shark is generally skinned on a platform, usually on the deck of a fishing boat. It can also done by suspending the fish from a hook through the upper jaw or with the carcass lying belly down on the ground. A large and very sharp knife is used for the operation.

• Cut off all the fins except the tail.

• Insert the knife in the holes already made by the removal of the dorsal fins and cut forward to the upper front of the head and back to the knob near the tail.

• Cut off the tail just in front of the knob.

• Cut around the head, behind the gills and pectoral fins, then ventrally and forward around the edge of the lower jaw.

• Pull off the skin gently by freeing it from the carcass with the knife kept flat against the skin from the head towards the tail.

• To avoid ‘sour spots’ i.e. areas of tissue breakdown, skinning must be done within 30 minutes.

2. Soaking

• Wash the skin with seawater immediately after skinning to remove blood and slime. Washing with a hose is preferable.

• Immerse the washed skin in a 6% brine solution for 3-4 hours to facilitate fleshing.

3. Fleshing

• Fleshing is the removal of the residual tissue from the fleshy side of the skin after flaying. It is carried out with a ‘beaming knife’ and a stout ‘beaming board’. The beaming knife is a 40cm long, curved steel blade having a single edge and a handle at each end. A beaming board is made of hard wood and measures 1m wide by 1.5m long with a curvature across the width which matches that of the beaming knife.

• After fleshing the tail end of the skin is split by cutting around the ventral fin rudiments and vent and through the hole left by the anal fin.

4. Curing

• Immediately after fleshing, the skin is washed with seawater and drained for 10 minutes.

• Mineral salt is applied generously [about one third of skin weight] on the fleshy side and extra salt is rubbed along the cut edges. Salt must be neither powdered nor too coarse in nature.

• Lay the salted skins flat, one on top of the other, flesh side up with ample salt between each layer on a sloped platform so that the brine can drain away. The pile should not exceed 1.5m in height. The stacked skins must remain in this condition for a maximum period of 5 days. Complete protection from sun and direct sunlight must be maintained during this time.

5. Folding and storage

• At the end of the curing period the salted skins are removed one by one.

• The residual salt is shaken off from the cured skins and fresh salt is applied on the flesh side of the skin.

• The skins are folded with the flesh side inwards to prevent loss of salt, rolled into bundles and tied with twine.

• The bundled, cured skins are stored in a clean dry storage place after it has been disinfected with insecticides and fungicides.

3.3 Shark fins for soup

Large, edible species of sharks are used to obtain suitable fins. In India the fins of the following four species are usually collected for export:

• Hammerhead/round headed shark, Sphyrna zygaena

• Grey dog shark, Rhizoprionodon acutus

• Sharp-nosed/yellow dog shark, Scoliodon laticaudus

• Black-finned/black tip shark, Carcharhinus melanopterus

Equipment

• Wooden cutting board

• Large, broad-bladed, straight-edged knife

Procedure

• Wash the fish in running water to remove slime and dirt.

• Cut and remove the pectoral and pelvic fins on both sides.

• Cut and remove the dorsal fin and the tail.

• Remove the adhering flesh on the cut fins and washed them thoroughly in fresh water.

• Add salt to the fins in the ratio 10:1. Give the cut-sides of the fins a liberal sprinkling of salt and then apply a little lime. Leave the fins for 24 hours.

• Sun-dry the fins on clean mats until the desired level of 7-8% moisture is obtained.

• The fins are then packed, stored and exported according the buyers’ specific requirements.

3.4 Shark fin rays for soup

Fresh and dried fins of edible sharks can be used for extracting the rays.

Procedure

• Soak shark fins in clean fresh water, acidified to pH 2.5-5.0 with acetic acid for 48 hours.

• Scrape off the shagreen and continue soaking for 72 hours for fresh/raw fins and 120 hours for dried fins. The soaking is done to soften the fins.

• For over-dried/long-stored dry fins, heat the softened fins together with 10% acetic acid for 60 minutes.

• Separate the rays manually from the loosened flesh if individual rays are required and wash thoroughly in cold fresh water. In the case of tiny fins, the rays can be separated by gentle agitation using a mechanical stirrer.

• Dry the fin rays thus separated in the sun on mats spread on clean raised cement platforms until a moisture content of 5-8% is attained.

• Remove the dried fin rays from the sun and keep in shade for 30-60 minutes.

• Pack convenient quantities of dried fin rays in polyethylene bags.

• Store the dried shark fin rays in a dry, clean area.

3.5 Shark liver oil

Shark liver oil is used in the tanning and textile industries, as a lubricant and also as a rich source of vitamin A. The livers weigh 10-25% of the shark’s body weight and contain 60-70% oil. Indian sharks contain 2 to 180 kg of liver depending upon size, season etc.

The easiest method of extracting shark liver oil is to mince the livers and boil them with water in suitable containers. When the oil floats to the surface it is ladled off.

A more efficient method of extracting shark liver oil is by digesting the chopped livers with 1-2% by weight of sodium hydroxide or 2-5% of sodium carbonate at 82-85°C. During the operation continuous stirring is required. This method results in the dissolution of all proteinaceous matter and complete release of the oil. The oil is then separated using a centrifuge.

The oil is stored in barrels. For pharmaceutical grade shark liver oil the material is purified and bottled.

4 SHARK EXPORTS AND PRICES

Table 2 Shark exports: value and countries of destination

Table 3 Prices of shark products in rupees per kilogram

There exists considerable scope for substantially increasing the volume of India’s exports of shark products but no sustained, concerted efforts have been made to reach the maximum sustainable yield of this fishery.

5 REFERENCES

Bulletins published by:

• The Central Marine Fisheries Research Institute [CMFRI]

• The Marine Products Export Development Authority [MPEDA]

• The Central Institute of Fisheries Technology [CIFT]

Discussions with:

• Dr SG Silas, former director of CMFRI

• Dr Lekshminarayan, Senior scientist, CMFRI

• Mr VK Dey, MPEDA

• Mr Jagadish MPEDA

• A few technocrats associated with fisheries and fishery-related activities.