Coastal Aquaculture and Mariculture

Unit 5 - Major groups of Fisheries in India

5.3.1. Elasmobranch
Elasmobranchs are commonly called cartilaginous fishes as they posses certilaginous skeleton. This group consists mainly of sharks, skates and rays belonging to the families Carcharhinidae, Hemiscylliidae, Rhincodontidae, Sphymidae, Stegostomatidae, Hemigaleidae, Ginglymostomatidae, Triakidae, Rhincodontidae, Pristidae, Myliobatidae, Dasyatidae and Gymnuridae. The maximum size in sharks ranges from 70 cm (Rhizoprionodon oligolinx) to 2000cm (Rhincodon typus), in skates from 270 cm (Rhinaancylostoma) to 656 cm (Pristis microdon) and in rays from 70 cm (Dayatis kuhlii) to 204 cm (D. zugei). In the past, it was considered as low value species. It started gaining commercial importance in India only recently because of increasing demand for shark's fins in the Souteast Aisian countries. The sharks are predominant along the west coast (76%) while rays along the east coast.
Distribution
Global
They are distributed in the tropical, subtropical and temperate waters of the seas around the world.
India
They are found distributed along both the coasts from the near shore regions to oceanic waters. The commercial sharks are mostly found at depths varying from 15 to 150 mm while the rays and guitar fishes are at 4-150 m.
Common elasmobranch species
The dominant and commercially important species of elasmobranches which support fisheries are listed below.
Sharks
The dominant species of sharks are Chiloscyllium indicum (Slender bamboo shark), C. griseum (Grey bamboo shark), Rhincodon typus (Whale shark), Stegostoma fasciatum (Zebra shark), Carcharhinus brevipinna (Spinner shark), C. dussumieri (White cheek shark), C. limbatus (Black-tip shark), C. macloti (Hard- nose shark), C. melanopterus (Blackfin reef shark), C. sorrah (Spot-tail shark), Galeocerdo cuvieri (Tiger shark), Rhizoprionodon acutus (Milk shark), Scoliodon laticaudus (Spade-nose shark), Eusphyra blochii (Wing-head shark), Sphyrna mokarran (Great hammer-head) and S. zygaena (Smooth hammer-head).
Skates
Important species among skates are Rhina ancylostoma (Bow-mouthed angel fish), Rhinobatos granulatus (Granulated shovel-nose ray), Rhynchobatus djiddensis (White spotted shovel-nose ray), Anoxypristis cuspidata (Pointed saw- fish) and Pristis microdon (Small-tooth saw fish).
Rays
The important species are Aetobatus narinari (Spotted eagle ray), Aetomylaeus nichofii (Nieuhof's eagle ray), Rhinoptera javanica (Javanese cow-ray), Himantura uarnak (Honey combed sting ray), H. bleekeri (Whiptail sting ray), Dasyatis zugei (Pale edged sting ray), D. imbricatus (Schneider's scaly sting ray), Amphotistius kuhlii (Blue spotted sting ray), Pastinachus sephen (Drab sting ray/cow-tail ray), Gymnura poecilura (Long tail butterfly), G micrura (Short tail butterfly) and Mobula diabolus (Horny ray).
Production trend
The catchable potential of 64,934 t of elasmobranchs up to 50 m depth zone and 103,000 t from beyond 50 m have been estimated for the EEZ of India. There have traditionally been important fisheries for elasmobranchs in India with a relatively steady growth up to the mid 70's, followed by a period of stability during most of the 80’s, then a tremendous increase in catches in 1987 resulting in India becoming one of the top three elasmobranch producers in the last ten years. Indian production of sharks and rays represents 8.78% of the world elasmobranch catches. Still, because of large inland yields, elasmobranchs comprised only 1.72% of total national catches in 1987-1991. Catches from the west coast were slightly larger than those of the east coast during 1977-1991.
During 1983-1985 sharks comprised 55% of the elasmobranch catch of the country. The main fishing areas in order of importance were Gujarat, Maharashtra, Kerala, Andhra Pradesh, Karnataka and Tamil Nadu and important fishing grounds for sharks are reported for Ashikode, Kerala Province. Sharks, catches are incidental to other fisheries in India and are mainly taken with longlines, which vary in design by region, and are also as bycatch of trawlers using disco nets off Ratnagiri (Maharashtra), with bottom set gillnets in Porto Novo (Tamil Nadu) and by shrimp trawlers of Kerala. Rays are caught with bottom set gillnets in Gujarat, northwest India and Cudalore and are abundant on the outer shelf and slope off Kerala and Karnatakta. Batoids comprise 10% of bycatches in Calicut; 90% of the bycatch comes from trawlers, 8% from gillnets and 2% from hook and lines. Both sharks and- rays are abundant in Lakshakweep and form important by catches in trawl fisheries in Krishnapatnam.
Directed fisheries for sharks are developing on a seasonal basis on the east coast of India. About 500 vessels, both sail -powered and motorized, fish for sharks with bottom or drift longlines of the coasts of Orissa Andhra Pradesh and Tamil Nadu. Bottom longlines are usually set in waters 80-150 m deep and occasionally as deep as 500m and bull sharks and tiger sharks. The longlines have up to 400 hooks and the meat is usually salted on board during the trip. In Orissa alone, about 200 boats are engaged in drift longlining on a seasonal basis (December -March). The most common species caught by drift longlines are silky sharks and scalloped hammerhead sharks.
The Elasmobranch fishery is distinct from others by the following features.
The fishing is not restricted to any particular zone. It is distributed both in inshore and offshore areas. The fishery is operative almost throughout the year. The main fishing centers are: Bombay-Cambay area, Mangalore-Calicut zone, Tuticorin-Madras, Vishakhapatnam and West Bengal area. Of these, Bombay, Mangalore, and Tuticorin are the most important landing centres.
The fact that the elasmobranch fishes constitute an important marine fishery of India is borne out by the following landing figures of this class of fish in our country during the past few years.

Both the east and west coasts of India contribute equally towards the landings of these fishes and the fishery is independent of seasons. The statewise percentage contribution during 1961-2000 showed that Tamil Nadu ranked first (27%), followed by Gujarat (23%), Maharashtra (14%), Andhra Pradesh (13%), Kerala (12%), Karnataka (4%), Orissa (3%), West Bengal (2%), Goa (6%), Andaman and Nicobar (0.6%), Pondicherry (0.4%) and Lakshadweep (0.4%) during 1961-2000. Of the total elasmobranchs exploited in the country, the sharks constituted 62% followed by rays (34%) and skates (4%) during 1981-2000.

Mode of exploitation
The elasmobranchs are mainly exploited by shrimp trawlers (42%) followed by gill net (26%), hooks and line (16%), dol net (3%) and others (11%). Sharks are exploited by trawl net (32%), gill net (31 %) and hooks and line (20%), but shrimp trawl chiefly exploits skates (86%) and rays (67%).
Food and feeding habits
Elasmobranchs are carnivores and predaceous in nature, with the exception of Rhincodon typus (Whale Shark) which is mainly a zooplankton (filter) feeder. Sharks mainly feed on pelagic teleosts such as sardine, mackerel, Bombay- duck etc. and cephalopods (squid, octopus, and cuttlefish). Skates and rays mostly feed on benthic organisms viz. crustaceans, molluscs, polychaetes, amphipods and teleosts (Apogon spp, Nemipterus spp., sciaenids)
Spawning season
The majority of species of ealsmobranchs in the Indian seas are viviparous, some are oviparous and few are ovo-viviparous. The breeding season of various species belonging to sharks, skates and rays vary. However, the majority of species breed during pre-monsoon (January-May) and post-monsoon (September- December) and few in monsoon (June-August) period.
Vivparous: Grey sharks, hammerheads, Galeorhinus,Hemitrikis, Hypogaleus and Logo
Ovovipiparous: Filled sharks, cowsharks, bramble sharks, squalids, gulper sharks, tiger sharks, electric rays, sting rays, guitar fishes and saw fishes.
Oviparous: Whale shark, Zebra shark, bamboo shark, nurse sharks and skates of the family Rajidae
Fecundity
All the species of elasmobranchs have low fecundity. The number of young ones (pups) in shark species ranges from 1-2 in Scoliodon walbeehmi, 26- 44 in G. cuvieri, in rays it is in Dasyatis walga, 1 -4 in Gymnura poecilura and in skates 6 (Pristis cuspidatus) to 12 (Rhinobatos granulatus). In rays, the number of pups varies from 1 (Dasyatis walga) to more than one 1-4 (in gymnura poecilura. In guitar fishes, the number of pups vary from (Pristis cuspidatus) to 12 (Rhinobatus granulatus).
Utilization
Elasmobranchs are valuable fish as almost every part of body is utilized for various purposes. The shark liver oil could become an important resource in the fight against cancer. It contains alkysoksy-glycerol, which is said to strengthen the shark's immune defense system. It also strengthens tissues and has a favorable effect on patient lmdergoing radiation treatment. It is a source of vitamins A and D, used in textile, tanning, sanitary, cosmetic, etc. as ingredients in shoe-polish, French perfumery, phannaceuticals, as lubricant, for preserving boats, and in street lamps. Cartilages are used for fish meal, in medicine for cancer, bum victims, eye fatigue treatments. Fins are used for making soup and glue. Dried shark fins are exported in large quantities to Singapore, Malaysia, and Hongkong etc. Skin (used for making a variety of leather products such as hand bags, belts, shoes, sanding the wooden boats, etc.), teeth (in ornaments), jaws (tourist trade), meat (eaten in fresh or cured) and viscera (fish meal) are also utilised.
Even though the peculiar flavour of the fish is not relished by many fish eaters, the fresh meat is sold to some extent in internal markets. At present in the country, the salting and drying is done and are marketed as "Wet cured" or “dry- cured”. A method has been recently reported to eliminate urea almost completely from the flesh. The fish salted in the ratio of 1:4 (common salt: fish) is desalted for 24 hours in 5% brine, resulted in the ratio of 1:6 (salt to fish) for another 24 hours and dried in sun, when the urea is reduced to negligible quantities. Dry cured cartilaginous fish finds good markets in Sri Lanka, Burma, and Singapore etc. Shark meat is also used for the production of minced fish products such as fish balls, fish cakes, fish sausage, and tempura, surimi for ham and fish paste.
Marketing
The products exported from India are frozen shark meat, gutted finless sharks, shark tails, dried shark fins, shark fin rays, and shark bones. Export of shark products increased from 386 tonnes to 1,508 tonnes and the value from Rs. 9.5 to Rs. 35.49 crores during 1996-97 to 2000-01. Shark fins and fin rays are traditionally consumed in Hong Kong, Singapore, Taiwan, China and other countries. Sri Lanka, Taiwan, Korea and Singapore import shark meat from India. The biggest market for shark -liver oil and skin is Japan and Nepal.
Management
Many species of sharks and rays use the bays and estuaries, as nursery for early growth of their young ones and hence fishing has to be regulated in these areas. Since the peak period of spawning in elasmobranchs coincides with the monsoon season, a restriction on trawling during such times would prevent recruitment overfishing and growth overfishing. Some species of elasmobranchs school by age, sex and reproductive state. They should be protected from intense fishing. As the rate of reproduction in rays is extremely low, precaution should be taken to prevent over exploitation. Whale sharks are few in numbers. Hence the ban on fishing should be continued to help resuscitation of the stock.