Biodiversity Conservation Using "Bycatch Reduction Devices" (BRDs), In Fisheries

Dharmendra Kumar Meena., ¹ Debabrata panda., ¹ Amiya Kumar Sahoo., ¹ Bijay Kumar Bahera¹.

1. Central Inland Fisheries Institute, Barrackpore, Kolkata, 700 120

Corresponding author:- Dharmendra Kumar Meena

* Email : dkmeenafnb@gmail.com

Introduction

In simplest term bycatch refers to non-targeted species retained, sold or discarded for any reason (Alverson et al., 1994).Bycatch includes both discarded and retained incidental catch of non-targeted finfishes and invertebrates, as well as also involve endangered, threatened or protected species. 'Incidental catch' is the retained catch of non-targeted species and 'discarded catch' is that portion of catch returned to the sea because of economic, legal or personal considerations. Fisheries bycatch has been identified as a primary driver of population declines in several species of marine mega-fauna such as elasmobranchs, mammals, seabirds and sea turtles.

Present bycatch in Indian and world fisheries

Pramod (2010) estimated the bycatch discards from mechanised trawlers operating in Indian EEZ at 1.2 million tonnes. The Global bycatch by the world's marine fishing fleets was estimated at 28.7 million t in 1994, of which 27.0 million t (range : 17.9-39.5 million t) were discarded annually and shrimp trawling alone accounted for 9.5 million t (35 %) of discards annually. In 1998, FAO estimated a global discard level of 20 million t (FAO, 1999). Average annual global discards, has been re-estimated to be 7.3 million t, based on a weighted discard rate of 8%, during 1992-2001 period (Kelleher, 2005).

Bycatch solution

Bycatch reduction has been attempted by (i) a reduction in the overall fishing effort by removal of excess capacity, regulatory bans, trade related measures and consumer behaviour, (ii) a reduction in bycatch per unit effort by technological interventions and (iii) management actions. Various types of bycatch reduction technologies have been developed and deployed in the fishing industry around the world.

Bycatch reduction in trawl fisheries

The trawls in general and shrimp trawls in particular have poor selective characteristics. Some of the advantages in reducing the amount of unwanted bycatch caught in trawls are (i) reduction in impact of trawling on non-targeted marine resources, (ii) reduction in damage to shrimps due to absence of large animals in codend, (iii) shorter sorting times, (iv) longer tow times, and (v) lower fuel costs due to reduced net drag. Operation related approaches to bycatch reduction include appropriate choice of fishing area, fishing depth and fishing time and season. Gear related approaches include trawl design improvement, mesh size optimization, br catch reduction devices.

Mesh size regulation is a common measure for reducing the bycatch of juveniles and small sized non-target species in trawls and is an important step towards reducing the growth overfishing, rampant in Indian fisheries. The use of square mesh instead of traditional diamond mesh generally increases selectivity, in respect of many species (Boopendranath and Pravin, 2005).

Bycatch Reduction Devices

Devices developed to exclude the endangered species like turtle, and to reduce the non-targeted species in different gear systems are collectively known as Bycatch Reduction Devices (BRDs). BRDs can be broadly classified into three categories based on the type of materials used for their construction, viz. Soft BRDs, Hard BRDs, and Combination BRDs. Soft BRDs make use of soft materials like netting and rope frames for separating and excluding bycatch. Hard BRDs are those, which use hard or semiflexible grids and structures for separating and excluding bycatch. Combination BRDs use more than one BRD, usually hard BRD in combination with soft BRD, integrated to a single system. The salient features of some of the important BRDs are described in the following sections.

Escape windows and square mesh codend

Escape windows made of large square mesh netting (square mesh window) or parallel ropes (rope BRD) or simple slits (bigeye BRD) or rigid windows (fisheye BRD) are provided on the upper side of the codend or belly and they function based on the differential behavior of fishes and shrimps. Fishes that have entered the codend tend to swim back and escape through the openings, at the top in the front section of the codend. The square meshes have the advantage that the mesh opening is not distorted while under operation, unlike diamond meshes. The codends made of square meshes maintains a cylindrical shape while the diamond mesh codend assumes a bulbous shape with the accumulation of catch.

Radial Escapement Section

A radial section of netting with large meshes or parallel ropes is provided between hind belly and codend. Small sized fishes, jelly fish and other bycatch components which have low swimming ability are expelled due to enhanced water flow through large mesh section. Often, a funnel made of small netting is provided to accelerate the water flow inside the trawl and guide the fish towards the codend. Actively swimming fishes swim back and escape through the large mesh netting section surrounding the funnel, where the water flow rate is weak, while the shrimps are retained in the codend. Studies using Radial Escapement Device have shown 20-40% reduction in the fish bycatch (Boopendranath et al., 2008).

BRDs with guiding panels

Sieve nets (also known as veil nets) are cone shaped nets inserted into standard trawls which direct unwanted bycatch to an escape hole cut into the body of the trawl leading to a second codend. The large mesh funnel inside the net guides the fish to a second codend with large diamond mesh netting, while shrimps pass through large meshes and accumulate in the main codend. Bycatch exclusion rates of 15-50%, with shrimp loss of 5-15% has been reported in sieve net installed trawl operations in different fishing.

Rigid grid sorting devices

Several designs of rigid grid sorting devices have been developed for separation of shrimp from non-shrimp resources, such as Juvenile and Trash Excluder Device, (JTED) and Juvenile Fish Excluder cum Shrimp Sorting Device (JFE-SSD). Operations using rigid oval grid device has given a bycatch exclusion of about 64%, in Indian waters.

Juvenile Fish Excluder cum Shrimp Sorting Device (JFE-SSD)

CIFT has evolved a unique solution for this problem by developing the Juvenile Fish Excluder cum Shrimp Sorting Device (JFESSD). The JFE-SSD brings down the bycatch of juveniles and small sized non-targeted species in commercial shrimp trawl, at the same time enabling fishermen to harvest and retain large commercially valuable finfishes and shrimp species. In addition, the fishermen would benefit economically from higher catch values due to improved catch quality, shorter sorting time, longer tow duration, higher catch and lower fuel costs. JFE-SSD operations off Cochin (India) have realised bycatch reduction up to 43% with shrimp retention of 96-97%. 
 
 Juvenile and Trash Excluder Device (JTED)

It consists of three rectangular panels joined with hinges, installed in the trawl codend. The first two panels consisted of a framework of parallel vertical bars designed to allow fish to escape from the codend. The third panel consisted of a rectangular sheet of small-mesh netting to prevent escaped fish from re-entering the codend. The evaluation of JTED in Vietnamese shrimp trawl fishery has shown exclusion of 73% of juvenile fish, 16% of valuable fish, and 8% of shrimp, although most valuable fish and shrimp were smaller than the minimum legal landing size.

Turtle Excluder Devices

TEDs were introduced in US shrimp fishery in late 1980s. CIFT-TED is an efficient turtle excluder device developed at Central Institute of Fisheries Technology (Cochin, India) with focus on reducing catch losses, which is a cause of concern for trawler fishermen in adopting the device. CIFT-TED is a simple single grid, hard TED design with top opening. It consists of an oval frame measuring 1000x800 mm and is constructed with 10 mm & #248; stainless steel rod. Five vertical grid bars of 8 mm & #248; stainless steel rod are welded to the inside of the oval frame. The spacing between the deflector bars is 142 mm and the maximum spacing between the frame and the adjacent deflector bar is 90 mm. The frame was fixed in the TED extension at 45° angle. Catch losses during the experimental operations due to installation of CIFT-TED were in the range of 0.52-0.97% for shrimp and 2.44-3.27% for non-shrimp catch components ( Boopendranath et al., 2010b).

Bycatch reduction in purse seine fisheries

Purse seines like other surrounding nets are not selective. Special escape panels known as Medina panels, which are sections of fine mesh that prevent dolphins from becoming entangled in the gear, and back down manoeuvre have been deployed to prevent capture of dolphins in purse seines. Selection of mesh size for the purse seine appropriate for the target species, proper choice of fishing area, depth and season could also lead to better selectivity of purse seines.

Bycatch reduction in gillnets

Optimization of gillnet mesh size and hanging coefficient according to the target species and size group and judicious deployment of gill net in terms of fishing ground, fishing depth and season in order to minimise the gear interaction with the non-targeted species are important bycatch mitigation measures for gill net fisheries. Lost gillnets continue to gill and entangle fish and other marine organisms leading to unwanted mortality, this process called ghost fishing.  One approach to minimise ghost fishing by lost gill nets, is to use biodegradable natural fibre twines or time release elements to connect the netting to floats (Hameed and Boopendranath, 2000). Another approach to prevent ghost fishing is to locate and retrieve lost fishing gear.

Bycatch reduction in hook and line fisheries

Interaction with sea birds during long line operation are minimised using dyed bait, deploying bird scaring devices (streamers) in the area where bait is set and by using sub-surface setting chutes for operation of branch lines. Sub-surface setting chutes, bluedyed bait, weighted baits and side-sets were reported to have reduced the bycatch of seabirds in the Hawaiian longline tuna and swordfish fisheries. Sea turtle mortality in long line operations have been reduced by using circle hooks in place of conventional J-hooks.

Bycatch reduction in trap fisheries

Approaches to reduce bycatch in trap fishing include optimised trap design and trap mouth configuration according to the target species and provision of escape windows for juveniles and nontarget species in the design side and appropriate choice of bait type, fishing area, fishing depth, fishing time and season in the operational side to minimise gear interaction with non-target species.

Conclusion

Bycatch reduction technologies have been mandated and effectively implemented in several scientifically managed fisheries in the world. However, its adoption in less effectively managed fisheries with open access regime may require the active involvement of stakeholders in the process, supported by a system of incentives and disincentives and training. A rights based regulated access system based on a strong inclusive participatory system of management seems to be necessary for facilitating large scale adoption of bycatch reduction technologies. BRDs and TEDs most appropriate for the regional fishery conditions should be adopted and enforced legally, after careful scientific evaluation and commercial trials, in order to ensure long-term sustainability of fishery resources, protect biodiversity and safeguard sea turtles from accidental mortality associated with shrimp trawling. A National Plan of Action for bycatch reduction in fishing gears, particularly targeting trawling sector, is necessary for the sustainability of Indian fisheries. 

References

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2. Pramod, G. (2010) Illegal, Unreported and Unregulated Marine Fish Catches in the Indian Exclusive Economic Zone, Field Report (Pitcher, T.J., Ed.), Policy and Ecosystem Restoration in Fisheries, Fisheries Centre, University of British Columbia, BC, Vancouver, Canada: 29 p. 

3. Boopendranath, M.R and Pravin, P (2005) Selectivity of Trawls, Fish. Technol. 42(1): 1-10 

4. Boopendranath, M.R., Prakash, R.R. and Pravin, P. (2010b) A review of the development of the TED for Indian fisheries, Indian Ocean —South-East Asian (IOSEA) Marine Turtle MoU Website, www.ioseaturtles.org. 

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