In recent years, large quantities of low value bycatch (LVB) are landed by trawlers for use as

fish meal and in fertilizer. Several fish meal plants have been established and high demand

for the raw material is acting as an incentive for catching and landing large quantities of

LVB. In Karnataka (a coastal state along west coast of India) alone, the annual turnover of

fish meal and fertilizer plants is estimated to be around 270 million rupees (= 4.6 million

US$).The landed LVB is turning out to be a sizeable income to the trawl operators. There are

several concerns related to increasing bycatch of the trawlers. The bycatch is comprised of

a high percentage of juveniles of commercially important species, resulting in recruitment

overfishing. With the introduction of high speed semi-pelagic trawls, the adults of low-valued,

small-sized adult fishes are also removed in large quantities, impacting the coastal marine

resources. The current situation demands a robust management plan addressing the issues of

the bycatch and in this regard information on quantities, value and composition of lVB landed

and/or discarded, and seasonality of the catch are essential

Dineshbabu, A P

Thomas, Sujitha

Vivekanandan, E

CMFRI Digital Repository

109Regional Symposium on Ecosystem Approaches to Marine Fisheries & Biodiversity, October 27-30, 2013, KochiAssessment of low value bycatch and  its application for management of trawl fisheriesA.P Dineshbabu*, Sujitha Thomas and E. VivekanandanCentral Marine Fisheries Research Institute, Cochin 682018, India*Email: dineshbabuap@yahoo.co.inIn recent years, large quantities of low value bycatch (LVB) are landed by trawlers for use as fish meal and in fertilizer. Several fish meal plants have been established and high demand for the raw material is acting as an incentive for catching and landing large quantities of LVB. In Karnataka (a coastal state along west coast of India) alone, the annual turnover of fish meal and fertilizer plants is estimated to be around 270 million rupees (= 4.6 million US$).The landed LVB is turning out to be a sizeable income to the trawl operators. There are several concerns related to increasing bycatch of the trawlers. The bycatch is comprised of a high percentage of juveniles of commercially important species, resulting in recruitment overfishing. With the introduction of high speed semi-pelagic trawls, the adults of low-valued, small-sized adult fishes are also removed in large quantities, impacting the coastal marine resources. The current situation demands a robust management plan addressing the issues of the bycatch and in this regard information on quantities, value and composition of lVB landed and/or discarded, and seasonality of the catch are essential. To collect data on low value bycatch and discards, Mangalore Fisheries Harbour (in the southern coast of Karnataka) was selected. Monthly data on fishing effort, landings and catch composition were collected for four years (2008-2011) from commercial trawlers. The price of catch and bycatch were also collected. The data on landings were segregated as those landed for human consumption and the rest for uses other than direct human consumption, designated as low value bycatch (LVB). Data was also collected from a few trawl operators, who provided information on date, depth, location and time of each haul, net type, mesh size, total catch and discard. Along with this information, an unsorted portion of catch that would have been discarded at sea was collected as sample, which was representative of each haul. The data collected were used for the spatial mapping of juvenile abundance of a few dominant species.110 Regional Symposium on Ecosystem Approaches to Marine Fisheries & Biodiversity, October 27-30, 2013, KochiIt is estimated that the low value bycatch has substantially increased from 3,100 t in the year 2008 to 30,000 t by 2011. Over the years the discard from the trawl fisheries reduced considerably from 88% to 15%, resulting in landing of the bycatch (Fig.1). Established market linkages for the LVB has helped its efficient utilization and reduction of discards. With increasing number of fish meal plants, the demand for raw material has increased; and catching and landing of LVB is a source of enhanced income to the trawlers. The annual raw material requirement for the fishmeal and fish oil factories in Karnataka in 2012 has been estimated as 60,000 t. With only half of the demand is supplied now, capture and landing of LVB is likely to increase in future.In the ecosystem and sustainability perspective, incidence of large quantity of juveniles in the trawl bycatch demands intervention of specific bycatch management measures. Analysis of samples showed rich biodiversity of trawl bycatch, constituted by 204 species/groups, of which 95 species were finfishes, 20 belongs to molluscs and 27 were crustaceans. The threadfin bream Nemipterus randalli was the major species caught and the period of high incidence of juveniles of the species was during post monsoon months of September and October. Finfishes Fig.1. Contribution (%) of landed and discarded LVB by the trawlers of Mangalore Fisheries Harbour during 2008-2011have more demand from fish meal plants as they form better raw material for fishmeal and fish oil production. During 2008-2009, about 34% of the bycatch by weight and 44% by number were formed by juveniles of commercially important species. These results stress the need for reduction of juveniles of commercial species in bycatch to sustain the stocks. Information on seasonal availability of juveniles will be helpful in taking management decisions on the months of restriction of trawl operation to reduce the juveniles in trawl bycatch. Closure of nursery/spawning grounds or areas of special biological significance are effective options for reducing juveniles in the bycatch. With the GIS based resource mapping, seasonal and 111Regional Symposium on Ecosystem Approaches to Marine Fisheries & Biodiversity, October 27-30, 2013, Kochispatial abundance of juveniles of four key species forming commercial fishery were identified (Fig. 2). This will facilitate establishing spatial restrictions to reduce juvenile capture. Similar maps of juvenile abundance of other key species will be helpful to arrive at conclusions on spatial and seasonal fishing restrictionsReduced juvenile exploitation not only promotes sustainability of fish stocks, but also increases the profitability of the sector as larger fishes fetch better price. These measures are helpful for ecosystem-based management approaches and more fisheries can be managed through multispecies, multi-objective models with spatial component. To reduce the incidence of juveniles in bycatch, resource maps should be used as an excellent tool for the policy makers. It allows assessment of valuation of fishing grounds in terms of abundance of juveniles and adults. Illustrated maps with seasonal fishing grounds for juvenile exploitation would be a useful tool to educate the fishermen on the importance of protecting the areas of spawning and juvenile abundance if fish stocks. Fig.2. Spatio-temporal distribution of juveniles of important commercial finfishes in the trawling grounds off Mangalore.112 Regional Symposium on Ecosystem Approaches to Marine Fisheries & Biodiversity, October 27-30, 2013, KochiFishing in the Sundarbans, West Bengal  © Pradeep Vyas

Assessment of low value bycatch and

its application for management of trawl fisheries

The estimated annual average catch by trawlers operating from

Mangalore Fisheries Harbour (southwest coast of India) was

124,105 tonnes during 2008-2011. Of the total catch, 63.9% was

landed as high-value catch (HVC) for human consumption, 14.7%

as low-value bycatch (LVB), and 11.4% was discarded at sea.

However, during the four years, the contribution of LVB to the

trawl catch substantially increased from 2.5% to 24.6%; and the

discards reduced from 18.1% to 5.9%. As demand for raw material

from fish meal plants is increasing, trawlers are encouraged to

target LVB. Trawl bycatch consisted of 205 species/groups, of

which 147 were finfishes, 4 bivalves, 7 cephalopods, 21 crabs, 3

stomatopods, 3 lobsters and several miscellaneous groups. About

34% of the LVB by weight and 63% by number were juveniles of

45 commercially important species. Mapping spatio-temporal

abundances of juveniles of four important demersal fish species

showed that the distributions of juveniles occurred along vast

coastal stretches for several months in a year. Exploitation of large

quantities of juvenile and sub-adult fishes potentially contributes to

growth overfishing, reduced economic returns to fisheries and loss

of biodiversity; and therefore threatens the sustainable exploitation

of resources. A few potential management options such as the use

of bycatch reduction devices, spatial and temporal closures to

trawling and fisheries refugia are discussed. Assessing the net

economic value of benefits and losses due to LVB is required to

achieve sustainable management of trawl fisheries

Assessment of low value bycatch and

its application for management of trawl

fisheries

http://eprints.cmfri.org.in/10249/1/AP_Dineshbabu_JMBAI_56_2.pdf

Assessment of low value bycatch and its application for management of trawl fisheries

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