The Ecology of the SLBSC Fishery

33

e. The Ecology of the SLBSC Fishery

147 No data or information, either published or unpublished, is available describing the retained or discarded bycatch from the bottom-set gill net fishery for SLBSC. Chitravadivelu s 1993 paper describes the traditional box trap fishery Parik Koodu in Jaffna Lagoon. Unpublished papers by Sivanathnan, S., de Croos M. D. S. T. 2013 and Nadaraja, T. describe the bottom-set gill net fishery, but neither study addresses the issue of fishery bycatch. 148 On the Indian side of the IMBL, bottom trawling is the principal fishing method used to harvest BSC. Thus, no comparable data is available from the studies of the Indian BSC fishery, which could be used to assess the ecology of the SLBSC fishery. 149 Direct observations and interviews with fishermen and traders were used to generate a list of common plants and animals landed as bycatch from the SLBSC fishery see Table 8 below and right. Finfish species, representing in the region of 20 fish families were identified, either by direct observation or from the Tamil and Sinhalese names commonly used by fishermen in each district. Molluscs, particularly the woodcock murex Murex scolopax and the spider conch Lambis chiragra were commonly observed among the bycatch in Kalpitiya Puttalam District. 150 Semi quantitative data collected during the field survey suggests that the average weight of bycatch landed by fishermen in the four districts ranges from one to three kilos for finfish and crabs and five to seven kilos of assorted molluscs, depending on the location. The majority of the finfish in the bycatch are retained: either sold or consumed by the fishermen. In Kalpitiya and in Jaffna districts, molluscs are broken open or boiled and the meat is extracted and sold. 151 According to fishermen, nylon nets generated more bycatch than monofilament nets. A negative correlation between mesh of any type of net and bycatch was also suggested. As the mesh size of the bottom-set gill nets increases, the amount of bycatch is alleged to decrease. 152 A number of ETP species are known to be present in the vicinity of the SLBSC fishery in Palk Bay and the Gulf of Mannar Dayaratne P., et al. These include the dugong, the indo-pacific humpbacked dolphin and several species of turtle, sea snakes and shark. According to fishermen turtles are very rarely caught in bottom-set gill nets. The mesh size of bottom-set gill nets used to harvest SLBSC is fairly small and turtles generally feed in mid and surface water feeds Lalith Ekanayake pers. com.,. Small sharks are occasionally appear in the by catch. 34 Table 8 Marine fauna and flora observed or reportedly caught in bottom-set gill nets, together with observations on endangered, threatened and protected species Common Name Latin Tamil Sinhala Notes Vertebrates Finfish Sardinellas Amblygaster sirm Sardinella albella Sudai Salaya Retained Jacks Trevallys Caranx spp., Para Katta Paraw Retained Sting Rays Dasyatidae Thirrukai Maduwa Retained Emperor Fish Letherinus Vella Vellai Meevetiya Rare. Retained Poochel - - Spiny Flatheads Platycephalidae Aerial - Common. Discarded Illishas Ilish spp. Vellel poovelle Puvalaya As bokka Discarded - Vellal - - Rabbit Fish Signanthus Othi Ora Nava Retained Needlefish Belonidae Mural Habarali Retained Milk fish Chanos chanos Palmeen - Retained Barramundi Lates calcarifer Goduwa Motha Retained Barracuda Sphyraena spp., Seela - Retained Silverbiddies Gerres spp., Thirali - Retained Blo h s gizza d shad Nematalosa nasus Koimeen Suthara Sudaya Retained Catfish Arius spp., Keliru; Angulouwa - Discarded Moonies Monodactylidae - - Retained Grouper Serranidae Kossa Kallawah Rare - Juveniles only Seahorse Sygnathidae - - Very Rare. Discarded Sprats Thryssa spp., Poruva Lagaa Retained Mullet Mullidae Manalai Godaya Retained Invertebrates Mulluscs Woodcock Murex Murex scolopax - - Common – Kalpitiya Retained or Discarded Spider Conch Lambis chiragra - - Common – Kalpitiya Discarded Spiral Melongena Pugilina cochidium - - Discarded Chank Turbinella pyrum Kalanda - Common Retained Other Bivalves - - - Cockles Gafrarium tumidum Andra antiquate - - Retained Windowpane oyster Placina placenta - - Common – Kalpitiya Discarded Crustaceans Other Crab Species - - Common Slipper lobster Scyllaridae - - - Crab with a Cross On - - Common Echinoderms Starfish - - - Rare Sea Urchin - - - Rare Corals Plants Coral Fragments - - - Rare. Discarded Coraline Algae - - - Rare. Discarded Sea grass - - - Rare. Discarded 35 Common Name Latin Tamil Sinhala Notes ETP Species Sea Cows Dugong dugon - Mudu Ura Kalpitiya Only. Not caught in bycatch Indo-Pacific Humpbacked Dolphin Sousa chineusis Kadal Puni - Kalpitiya Only Not caught in bycatch Spinner Dolphin Stennella longirostris Green Turtle Chelanis mydas - Kesbewa Very Rare. Released Alive Turtles are protected species. Regulation is enforced. Hawksbill turtles have been known to feed on BSC Hawksbill Turtle Eretriochelys imbricota Olive Ridley Turtle Ledidochelys olivacea Sea Snakes 4 species Hydrophidae Potai pambu Kadal sarai Nalla waliki pam Valaikkadia; Badakaha Mudhu Naya Rare - Small mesh nets only Sharks Elasmobranchs Sura Mora Rare. Retained Small Sharks Only 153 A high diversity of critical marine habitats are located the vicinity of the SLBSC fishery, off the northwest coast of Sri Lanka. Critical marine habitats include islands, fringing mangroves, sea grass beds see right: sea grass washed up along the shore by rough weather, coral reefs, sandstone reefs, sand banks and shifting shoals. 154 The bottom-set gill net for SLBSC was not observed to cause nor was it associated with any damage or destruction of critical marine habitats in the Puttalam Lagoon, Dutch Bay and Portugal Bay in the Gulf of Mannar or in the Palk Bay. 36

f. Management of the Fishery