Fishing Craft and Gear for Small Pelagics

Transcription

1 Paper presented at the National Conference on Marine Fisheries and Fisheries Harbour Infrastructure, 7-8 February 2009, Fishery Survey of India, Mumbai Fishing Craft and Gear for Small Pelagics K. Devadasan and M.R. Boopendranath Central Institute of Fisheries Technology P.O. Matsyapuri, Cochin , India Small pelagics like oil sardine, mackerel, lesser sardines, anchovies, scads, horse mackerel and Bombay duck contribute more than 30% of the marine fish production, in India. These species have shorter life span, high growth rate and high fecundity and so have better resilience to fishing pressure. Though produced in bulk, their quayside prices are low and there is considerable wastage of fish. Enhanced production, value addition and total utilisation of small pelagics will help in reducing shortages in fish supply. In this paper, fishing craft and gear systems in vogue for harvesting of small pelagics in India and possible future developments are discussed. In addition to the existing bulk catching methods for small pelagics such as purse seining and ring seining, there is scope for (i) diversification of fishing effort for small pelagics by adopting semi-pelagic trawl system for the existing small-scale mechanised trawlers and (ii) limited and planned expansion to aimed midwater trawling using Intermediate range freezer trawlers, based on precautionary principles. Keywords: small pelagics, fishing craft, fishing gear. Potential catch of marine small pelagics in Indian EEZ, has been estimated at 1.3 million tonnes, which forms 33% of the total potential and 78% of the pelagic resource potential (Anon, 2000). Small pelagic are typically less than 30 cm in size. They occupy a low trophic level, have comparatively short life span, high fecundity and growth rate and hence better resilience to fishing pressure. Small pelagics include fishes such as oil sardine, other sardines, anchovies, shads, other clupeoids, mackerel, scads, horse mackerel and Bombay duck (Table 1). The present landings of small pelagics in India is about 0.95 million tonnes, which forms 40% of the total marine landings in India. Though produced in bulk, their quayside prices are low and there is considerable wastage of fish. Enhanced production, value addition and total utilisation of small pelagics will help in reducing shortages in fish supply. 1

2 Table 1: Potential estimates and current landings of small pelagics from Indian EEZ Species groups Potential yield a (tonnes) Average production b ( ) (tonnes) Oil sardine Other sardines Shads Anchovies Other clupeoids Mackerel Carangids (scads, horse mackerel, etc.) Bombay duck Total a Anon (2000); b CMFRI (2007) Annual landings, tonnes Oil Sardine Mackeral Bombayduck Total Fig. 1. Trends in landings of major small pelagics in India, (Source: CMFRI statistics) Fishing Craft and Gear for Small Pelagics - Present Scenario An estimated total of 2,38,772 fishing crafts of various sizes and classes are under operation in marine fisheries, consisting of 58,911 mechanised boats, 75,991 motorised crafts, 104,270 non-mechanised crafts (CMFRI, 2006). Major gear systems operated are trawls, purse seines, ring seines, bag nets, gillnets and traps. The existing fleet size (CMFRI, 2006) of mechanized vessels is in excess by 35% and motorized crafts by 46% 2

3 as per the optimum fleet size estimates (Devaraj and Kurup, 2000). The bulk of the small pelagics such as oil sardine, other sardines, anchovies, other clupeoids, mackerel, scads, horse mackerel are landed by purse seines, ring seines, trawls and gillnets and Bombay duck in bag nets (Dol nets). Purse seining and ring seining Sardines, mackerel and anchovies are predominantly caught by surrounding nets. Central Institute of Fisheries Technology (CIFT), Cochin developed and introduced a mini-purse seine, for operation from traditional motorized craft, during which came to be known as ring seines. This gear system of 250 x 33 m net offered an efficient alternative gear for operation from the traditional boat seine craft thangu vallom. Ring seines are roughly rectangular walls of netting rigged with floats and sinkers which after detection of the presence of fish are cast to encircle the fish school. In recent years, largescale expansion has taken place in fishing capacity, both in terms of capacity of individual vessels, horse power and total fleet size. Uncontrolled increase in gear dimension, since its introduction from 250 m to over 1000 m. and uncontrolled increase in installed horse power from 9.9 hp to 140 hp, has been causing environmental and conservation issues. There are over 2300 OBM ring seiners and about 600 IBM ring seiners operating in the southwest coast, targeting sardines, mackerel, anchovies and other small pelagics. In order to ensure sustainability, facilitate capacity management, resource and energy conservation, it is necessary to standardize the fishing systems, in terms of capacities, fishing power and energy use. A limited number of mechanised purse seines are in operation, off southwest coast, targeting sardines, mackerel, pomfrets, horse mackerel and other carangids. Most of these operate large mesh (45 mm) purse seines. Trawling Trawl nets are conical bag nets with two wings and a codend where catch is accumulated, operated by towing from one or two boats. Single boat otter trawling is the most popular method in India. Over mechanised trawlers are in operation in Indian waters. As trawl is non-selective gear, large quantities of small pelagic fishes are landed, when they are available in off bottom layers. These include fishes such as oil sardine, other sardine, anchovies, other clupeoids, mackerel, scads and horse mackerel. Dol netting Bombay duck are predominantly caught by stationary bag nets known as dol nets. There are 8862 mechanised dol-netters operating in India, with the majority in Maharashtra (4409), followed by Gujarat (2425), West Bengal (1692), Orissa (254), Daman & Diu (71), targeting mainly Bombay duck, with assorted bycatch small pelagics and non-penaeid shrimp. The Bombay duck fishery accounts for about 5% of the total marine fish production in India. The major gear used for Bombay duck is the set bag net locally known as dol net. The nets are operated 8 to 15 km from the coast at a depth of 10 to 45 m. The annual catch of Bombay duck is around 80,000 to 120,000 tonnes. A major problem encountered in this fishery is the incidence of juveniles and non-targeted 3

4 species in the catch. There is a need to modify the gear in order to reduce juvenile mortality and bycatch. The dol netters are small wooden fishing craft of 14.3 m overall length which are not fuel-efficient and do not have facilities for ice storage to preserve the catch. Gillnetting Gill nets are rectangular walls of netting kept erect by means of floats and sinkers and positioned in the swimming layer of the target fish, which catch the fish by holding them in the mesh by gilling. Small meshed gill nets are widely used in non-motorised, motorised sectors for harvesting small pelagics such as sardines, mackerel, anchovies and small carangids. Scope for Diversification and Expansion in Fishing Craft and Gear for small pelagics The surrounding nets such as purse seines and ring seines will continue to be important gear systems for bulk catching of small pelagics in the mechanised and motorised sectors. Trawls in mechanised sector and small-meshed gill nets in the motorised and non-motorised sectors also will continue to be deployed for harvesting small pelagic resources. There is scope for (i) diversification of fishing effort for small pelagics by adopting semi-pelagic trawl system for the existing small-scale mechanised trawlers and (ii) limited expansion to aimed midwater trawling from Intermediate range freezer trawlers, based on precautionary principles. Fuel-efficient Fishing Vessel CIFT has developed and popularized 12 standard designs of fishing vessels in the size range m, suitable for various types of fishing under the Indian conditions. Percentage of fuel cost in the operational expenditure of trawlers may vary between 45 and 75 %, depending on installed engine power and duration of voyage. Hence most potential for fuel conservation exist in trawling. The hydrodynamics of the fishing vessel is the critical factor determining fishing efficiency. Fuel conservation will help not only in reducing the cost of fishing but also the level of environmental pollution. In the context of global energy crisis, CIFT has taken initiative to develop fuel efficient fishing vessels. A 15.5 m multi-purpose deep sea fishing vessel Sagarkripa with steel hull and energy saving features was designed and constructed. The design features include optimized hull design, optimized installed engine power, fuel efficient propeller and propeller nozzle. Commercial trials using the vessel by the fishing boat operators have confirmed about 17% savings in the fuel cost, compared to traditional designs of steel trawlers of the same size. This means substantial reduction in the operational cost and consequent improvements in net profits for the fishermen and minimization of environmental pollution. Such vessels could be deployed with advantage for harvesting of small pelagics using semi-pelagic trawls in the small-scale mechanised sector. Vessels of this type of design are coming up in southwest coast and Saurashtra coast. 4

5 Fig. 2 Fuel-efficient fishing vessel designed by CIFT for small-scale mechanised sector Semi-pelagic trawl system for small-scale mechanised sector Trawling industry in India is shrimp-oriented, due to its economic importance and export value. The Indian trawler fishermen cannot depend on shrimp alone for viable commercial operations any more, due to proliferation of trawlers and overfishing of target resources. Trawler fishermen require to adopt appropriate fishing gear to expand their reach to harvest large demersal and semi-pelagic species which are beyond the reach of currently existing designs of shrimp/fish trawls. Responsible fishing regime, which is promoted in India and around the world, requires that selectivity of the gear has to be improved and its negative environmental impact has to be reduced, in order to protect the biodiversity and environment and to ensure long-term sustainability of the fishery resources. CIFT has developed semi-pelagic trawl system, for the benefit of the mechanized trawling sector, in this context (Anon, 2006). Semi-pelagic trawling of different designs are in use in Australian and North-Atlantic waters, targeted at blue whiting, silver smelt, Atlantic mackerel and other pelagic and semi-pelagic resources, prevalent in these waters. CIFT Semi-pelagic Trawl System (CIFT SPTS-I) has been developed as an alternative to shrimp trawling in the small-scale mechanized trawler sector, after extensive field trials and observations onboard the departmental fisheries research vessels at Cochin (Kerala) and Veraval (Gujarat) and Fisheries Oceanographic Research Vessel Sagar Sampada of Centre for Marine Living Resources & Ecology (CMLRE) (Ocean Science and Technology Department, Ministry of Earth Sciences). It is capable of attaining catch rates beyond 200 kg.h -1 in moderately productive grounds and selectively harvest semi-pelagic finfishes and cephalopods, which are generally beyond the reach of conventional bottom trawls, currently used in commercial trawl fisheries in India. 5

6 The gear system consists of an 18 m four panel semi-pelagic trawl with double bridles, front weights and vertically cambered high aspect ratio otter boards (trawl doors) of 85 kg each. The system has been developed and optimized taking into consideration biological, behavioural and distribution characteristics of tropical demersal and semipelagic finfish and cephalopod resources and technical capabilities of the small-scale mechanized trawler fleet, operating in Indian waters. CIFT SPTS-I has shown significant resource specificity for fast swimming finfishes, which exhibit shoaling characteristics. Due to higher vertical opening up to 4.0 m realized in CIFT SPTS-I, resources that are beyond reach of conventional bottom trawls, could be efficiently harvested. Significantly high sheer-drag ratio of vertically cambered high aspect ratio otter boards, makes the system energy-efficient, compared to conventional flat rectangular and V-form otter boards. Aimed Midwater Trawling Pelagic species are generally fast swimming. They form dense shoals during daytime and respond to stimuli collectively. Pelagic fishes posses well developed sight and hearing capabilities. Midwater trawling is most successful when shoals are dense and large; when fishes are less active due to low ambient temperature or physiological states such as non-feeding, spawning or spent conditions; and when visibility is poor leading to slower responses of fish. Main design requirements for midwater trawls are high stability, large mouth opening, low turbulence and low drag. Midwater trawls require largest possible opening of the mouth, permitted by the available towing force of the vessel at the required towing speed, allowing roughly 30% margin of reserve power for gear manoeuvre during operations. The large mouth opening is usually achieved by the incorporation of large side panels. Wings are consequently reduced in size or absent altogether in the mid-water trawl, unlike the bottom trawl. The mouth opening may be oval, circular or square depending on the design and rigging. In some designs of surface operated trawls, the lower panel is extended ahead of the head rope. This is to counteract the tendency of pelagic fishes to dive downwards in response to disturbance caused by the approaching trawl. In aimed midwater trawling, the vessel is steamed towards the shoal of the target species after its location by sonar. At a reasonable distance from the target shoal, the gear is shot and its position under water is adjusted so as to take in the shoal. The fishing depth of the trawl is adjusted by varying vessel s speed and the length of the towing warps, either singly or in combination, for quicker response. The net monitor (net sonde) attached to the head rope of the trawl provides the data on the fishing depth, vertical opening of the net mouth and the catch entering the net, which are required for successful gear manoeuvre, based on data from sonar and echo sounder. Additional sensors in net monitoring system could provide data on the horizontal spread of the trawl mouth and at otter boards, in-situ temperature and catch increment in the codend. 6

7 Fig. 3 A catch of 22 tonnes of horse mackerel (Megalaspis cordyla), obtained during aimed midwater trawling, off west coast of India As there is intense concentration of effort in the bottom trawl fisheries, it could be advantageous from the resource management perspective and also from the energy conservation point of view, to encourage diversification to midwater trawling, in a controlled manner without compromising on sustainability of resources. Stern trawler does not require any large-scale modifications in structure or deck layout, for undertaking midwater trawling. However, the vessel must be large enough, highly manoeuvrable and sufficiently powered to tow a large mouthed midwater trawl at speeds exceeding 4.5 knots; should be equipped with acoustic fish detection (sonar) and trawl monitoring systems (net monitor or net sonde); and, in addition, must have provision for handling and preserving high volume landings. CIFT investigations onboard Intermediate freezer trawlers in the north-west coast during has indicated that mean daily landings of over 20 tonnes are possible for species such as horse mackerel and scad (Fig. 3). Midwater rope trawls were operated successfully during Indo-Polish Industrial Fisheries Survey, along the north-west coast of India for pelagic resources such as horse mackerel, ribbonfish, elasmobranchs, pomfret, catfishes and carangids (Dwivedi et al. (1977). The typical trawler for aimed midwater trawling may have a length overall of about 60 m, gross registered tonnage of 1900 and installed engine power of 2400 hp, with facilities for freezing and bulk storage of the catch. References Anon (2000) Report of the Working Group on Revalidation for Revalidating the Potential of Fishery Resources in the Indian EEZ, Department of Animal Husbandry and Dairying, Ministry of Agriculture, New Delhi Anon (2006) CIFT introduces eco-friendly semi-pelagic trawl system (CIFT-SPTS-I) for small-scale mechanized sector, Fish Technology Newletter XVII (2):

8 CMFRI (2006) Marine Fisheries Census 2005 Part-1, Central Marine Fisheries Research Institute, Cochin: 97 p. CMFRI (2007) Annual Report, Central Marine Fisheries Research Institute, Cochin: 151 p. Dwivedi, S.N., Radhakrishanan, N., Sulochanan, P., Nair, M.K.R., Joseph, A.(1977) Indo-Polish Industrial Survey along North-west Coast of India, Report No. 3, Exploratory Fisheries Project, Bombay. Kurup K N and Devaraj N (2000) Estimates of optimum fleet size for the exploited Indian shelf fisheries, Mar. Fish. Inf. ser. T&E No. 165, July-Aug-Sept 2000, CMFRI, Cochin: