MARINE FISHERIES KARTIK
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.