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9. Discards and bycatch in Shrimp trawl fisheries.

The highest rates of incidental catch of non-target species as identified by Alverson et al (1994) and other workers is associated with shrimp trawling. The use of selection technology in reducing the incidental catch of non-shrimp in temperature waters does, however, seem to be affecting the amount of bycatch discarded and recent evidence, suggests that in many parts of the world tropical shrimp bycatch which was once discarded is now being utilised. The figures which suggest that large quantities of fish are wasted in certain regions may be over estimates because it had been assumed that non-shrimp catches from tropical shrimp fisheries was automatically equated to discards. (See Table 11)

Alverson et al for instance suggest, that in the Northwest Pacific 97% of the shrimp bycatch is discarded producing over 4 million tonnes of waste fish. This however is countered by information provided by Zhou and Yimin (1996) who suggest that the Chinese shrimp trawl fleet discards very little of the non-shrimp catch. According to Zhou and Yimin the shrimp fishery of China catches about 1.8 million tonnes of bycatch all of which is used, much for feeds for the Chinese aquaculture industry. In S E Asia there has also been a growth in recent years in industry’s which use bycatch from shrimp fisheries for human consumption (Chee 1996).

Recent (1997) evidence from the countries of central America and the Caribbean suggest that the amount of incidental catch that is now utilised in the region is greater than that suggested by Alverson et al. In countries such as Belize, Colombia, Costa Rica and Nicaragua for instance it seems that between 20 and 30% of the once discarded bycatch is now utilised and in Venezuela it is probably at least 30%. In Guyana and Brazil the amount of utilisation has increased and probably now accounts for about 10% of the incidental bycatch. In Cuba where the state operates fishing, marketing, processing and distribution it is thought that virtually all edible bycatch is now used which probably accounts for up to 70% of the non-shrimp catch. (F Teutscher, Pers comm.) These figures seem to contradict the blanket figure of 3% utilisation that Alverson et al suggested for the whole of the West Central Atlantic, and perhaps indicate fuller use of the catch in a similar fashion to the trends seen in South East Asia. See Table 11 below.

The trend for greater and more complete utilisation of bycatch has been noted over the years and as Andrew and Pepperell (1992) state "It seems likely.......that the utilisation of by-catch will increase as demand for protein escalates and the retention and processing of by-catch becomes more economically viable".

    Table 11 : Estimated bycatch and discard levels from shrimp fisheries of the world


    Estimated Bycatch

    Estimated Discard

    Percent Discarded

    N W Atlantic




    N E Atlantic




    W C Atlantic




    E C Atlantic




    Mediterranean/Black Sea




    S W Atlantic




    S E Atlantic




    W Indian Ocean




    E Indian Ocean




    N W Pacific




    N E Pacific




    W C Pacific




    E C Pacific




    S W Pacific




    S E Pacific






    Based on: Alverson et al Table 4

9.1 Temperate waters

9.1.1 Pandalus

In temperate waters there has been extensive introduction of selector devices in trawls in recent years which have enabled reduction in the catch of non-target species to be made. This work centres around the use of the Nordmøre grate which originated in Norway as a means of reducing the capture of jelly fish but it was also found that incidental catch of fish was reduced without substantial reduction in the catch of shrimp. (Isaksen 1996) The technology has been further developed in particularly Norway, Canada and Australia and incidental catches have now been reduced in the shrimp fisheries of various regions. The grate works by separating active swimming fish, which will swim out of the net to avoid passing through the grate, from passive shrimp which will pass through the grate into the cod end. The device not only greatly reduces the catch of unwanted fish but will also lead to better quality catches, because less large objects get mixed with the shrimp in the cod end and less time is required on hauling and to sort out the catch before preservation. (Løbach and Viem 1996). In addition it has been suggested that fish escaping from nets fitted with the grates have a high survival rate, particularly compared with fish which escape through the meshes of the cod end of a trawl, which can be so damaged and traumatised by the experience that there chances of long term survival are much reduced. (Vold Soldal & Engås 1997)

In the northern Pandalus borealis shrimp fishery of Canada bycatch, particularly of redfish, has been almost eliminated by the use of Nordmøre grates, and new fisheries for shrimp have been opened up in Canadian waters which were not practised before because of high bycatch rates. Bycatch has been reduced from over 20% to less than 5% of total catch in some instances. In 1993 Norway and Russia agreed to introduce compulsory use of the grates in the shrimp fishery in both their EEZ’s as well as around Svalbard and their use is mandatory from January 1997 on bottom trawls in the Barents Sea. The use of the grate is now also compulsory in many of the northern shrimp fisheries of the United States of America, Canada and Iceland.

9.1.2 Nephrops

The Nephrops norvegicus fisheries in the North Atlantic and North Sea also produce bycatch some of which is discarded. The Belgian fishery, according to Redant and Polet (1994), discards very small numbers of undersized cod, plaice and sole but there are sometimes discards of large numbers of whiting and dab, depending on area fished and season. However the fishery catches as a matter of course white fish such as cod, plaice and sole for sale when at or above legal size and gunards and dabs are also sold on local markets as well as Nephrops which is the nominal target catch. Figures for the landings (1993) of the most important fish in the catches show that Nephrops in fact only constitutes just over 35% of the landed weight and just under 50% of the value. (See Table 12 and Table 13) It appears, therefore, that the fishery does not target Nephrops exclusively and will react to market demands, auction prices and the catch rates of Nephrops, targeting other species or fishing other grounds for other species. The regulation concerning landing sizes for the various round and flat fish caught along side the Nephrops dictate or influence the amount of these species discarded. The authors estimate that discarding of undersize and unmarketable whiting by the Nephrops fishery, although amounting to large numbers per year, is small in comparison to discards of whiting from other fishing activities and that probably the discarding of undersize cod, plaice and sole are negligible in comparison with others sources of discarding. This case illustrates the problems associated with the definition of target and non-target species in fishery. The fishery in this case is called the Nephrops fishery but the figures suggest that if only Nephrops was caught and marketed it would not be viable.

Table 12 - Top ten species in the landings of the Belgian Nephrops fishery 1993 (tonnes)


Landings tonnes

% age of landing






















Grey Gunard









Table 13 - Top ten species in the landings of the Belgian Nephrops fishery 1993 in terms of auction sales figures


Sales Million BEF

% age of landing































BEF = Belgian Francs

This situation in the Belgian Nephrops fishery seems to contrast with others. Evans et al (1994) report that only 12% of the catch in the Nephrops fishery of the Farne Deep (North Sea) is Nephrops and that a large number of other species, both vertebrates and invertebrates are also caught. Although some lemon sole, plaice, whiting, cod, haddock and sting ray are landed the vast majority of the bycatch was juvenile fish of species of no commercial value and discarded. They conclude that most of the fish was dead before being discarded and much was scavenged by sea birds.

Thorsteinsson (1992) asserts that capture of small haddock has often been a problem in the Icelandic Nephrops fishery. A double trawl one with square mesh window of 135 mm mesh proved that the window allowed the effective release of small haddock and whiting and some cod. All Icelandic Nephrops trawlers were obliged to use such windows very soon after the work concluded.

It seems therefore that progress is being made in eliminating or very much reducing discards in shrimp fisheries in temperate waters. This is happening through the use of selection devices such as the Nordmøre grate in the North Atlantic and Australian waters or by the fuller use of fish that is caught alongside the target species. The use of square mesh panels in Nephrops trawls seems to hold some promise for reducing non-target catch and is being introduced in some fisheries. In others however the catch of non-primary target species actually make valuable contributions to the commercial viability of the fishing units.

9.2 Tropical and subtropical waters

The Nordmøre grate in its original configuration works by excluding large specimens and retaining the smaller ones which are allowed to pass into the cod end of the trawl net. In tropical shrimp fisheries the shrimp are generally part of a species assemblage where the size of the target shrimp overlap with the size of the fish that need to be excluded and it is often, in fact the smaller specimens that need to be excluded from the net. The size characteristics, therefore, of the species flock and behavioural differences between shrimp and fish mean that the direct transfer of this technology has not been possible into tropical fisheries although some work is continuing in this field with the use of a grids and other devises mounted in the top panel of tropical shrimp trawls allowing the smaller fish and shrimp to escape, showing some promise.

The public conception of the problem of bycatch in tropical shrimp fisheries is, however, different from that associated with the problem in temperate fisheries. It is a fact that many of the tropical shrimp trawling activities take place in waters adjacent to low income, food deficit countries. The pressure in this scenario is not, necessarily, to stop the bycatch being caught but to make use of it for feeding people once it has been caught. Work, for instance, on the use of grid technology in the shrimp fishery of Mozambique was focused on the reduction of catches of "only the very smallest the intention of a newly approved project was to take care of and process most of the bycatch taken by the shrimpers" (Isaksen and Larsen 1993) In this case, in the final analysis it seems, that the Mozambique government were reluctant to introduce a top mounted grid in trawls as it reduced incidental fish catch too much. They preferred instead to look further at a larger size cod-end mesh which reduced only the catch of the very smallest fish and shrimp and retained the large valuable shrimp for export and the fish which could be used for local consumption (R Larsen, Pers comm.)

9.2.1 Species composition

An analysis of the literature reporting the species composition of bycatch in tropical shrimp trawl fisheries shows that there are a large number of species represented in the bycatch but that they represent a relatively small number of families and that some families are found in the bycatch in many parts of the world.

Table 14 below illustrates the commonality of families that occur in the bycatch of shrimp trawlers throughout the topical world. For instance Ariidae (Marine Catfishes), Carangidae (Jacks), Clupeidae (Herrings, shads, sardines, menhaden), Gerreidae (Mojarras), Sciaenidae (Croakers), Trichiuridae (Ribbon Fish) are found in bycatch in all the regions shown in the table. Other species groups such as the Leiognathidae (Pony Fish) are not so wide spread but where they are found can make up large proportions of the non-target catch.

Table 14 - Families of fish reported as tropical shrimp trawl discards/bycatch

Family Name

Bay of Bengal

Indonesia Australia

S China S

Gulf of Mexico


E Africa / Indian Ocean

Arab Gulf

West African coast

Ariidae Catfish              
Bothidae Flounders              
Chirocentridae Wolf Herring              
Cynoglossidae Soles              
Engraulididae Anchovy              
Gerreidae Mojarras              
Haemulidae Grunts              
Leiognathidae Pony Fish              
Lutjanidae Snappers              
Mullidae Goatfish              
Muraenescidae Eels              
Nemipteridae Threadfin Breams              
Platycephalidae Flatheads              
Polynemidae Threadfins              
Priacanthus Bigeye              
Sciaenidae Croakers              
Scombridae Mackerels              
Serranidae Groupers              
Sphyraenidae Barracuda              
Stromateidae Pomfrets              
Synodontidae Lizard Fish              
Trichiuridae Ribbon Fish              
Sources: Alverson et al (1994); Papers from: Gulland and Rothschild (1982); U Khum Mg Aye (1995); Chee (1996); Bejei (1980); Barratt (1986); Hendrickson and Griffin (1993); Gordon (1991); Feidi 1989

Andrew and Pepperell (1992) conclude that the four main characteristics of shrimp bycatch are:

  1. Fin fishes make up the majority of the catch in many shrimp fisheries.
  2. The sizes of the fish are generally small <20 cm and often of similar size to the shrimp.
  3. A relatively small number of species of fishes may dominate the by-catch.
  4. Several families of fish are abundant in the bycatch of many of the worlds shrimp fisheries (such as sciaenids, pomadasyids, sparids, synodontids, serranids, bothids, and nemipterids)

9.3 The early work on tropical shrimp bycatch use

In the 1970’s the growth of shrimp fisheries in tropical and warm waters and the perceived growth of demand for animal feed stuffs in those countries with growing shrimp fisheries led to the search for means of utilising bycatch for animal feeds. Experiments on the production of fish silages or fish hydrolysates based on methods already used in Denmark and Poland were made. (Disney et al 1978) The goal of this work was to produce a simple technology that could be used on a small scale in tropical fisheries where the main source of raw material was to be found. The use of organic and inorganic acids or the use of acid producing bacteria were investigated which, when added to a mixture of small fish, would produce an stable liquid which could be incorporated into animal feeds. This work in UK, Indonesia, Hong Kong, Sri Lanka, Australia and elsewhere suggested that it was technically feasible to produce such products and that they had potential as feeds for livestock. However the uptake of this technology in tropical shrimp fisheries has been small. In spite of the fact that the technology is simple it still requires the supply of acids or acid producing bacteria, a change in the way in which animal feeds are produced (since a liquid rather than a solid are made) and extensive training of potential users. Twenty or more years since the first work was done and there are few if any examples of its uptake in the target communities.

In the late 1970’s and early 1980’s the focus had changed in the search for answers to the utilisation of shrimp bycatch. The proceedings from a conference in Guyana in 1981 (IDRC 1982) illustrate that workers were now looking at the use of bycatch to produce new products mainly for human consumption. The products under investigation sought to disguise the original fish by the production of minced products from the flesh either as salted products (Young 1982, Bligh and Duclos 1982) or as frozen minces (Tan at al 1982, Productos Pesqueros Mexicanos 1982, Tableros and Young 1982). Other investigations used existing technology to endeavour to make products resembling existing products such as canned pates, sausages, frozen fish sticks etc. (Poulter 1982). Recent evidence suggests that very few of these technology lead initiatives have provided long term solutions to the use of bycatch with few examples of products still being made commercially.

9.4 Gulf of Mexico and South Atlantic prawn fisheries of the United States

A study conducted by the Gulf and South Atlantic Fisheries Development Foundation into bycatch reduction devises applicable for use in the Gulf of Mexico and the South Atlantic Shrimp Fisheries analysed in some depth the species composition and quantity of catch in the two fisheries. The study was prompted because of concern that shrimp fishing may have been contributing to over fishing of commercially important species through capture of juveniles of those species. Capture of juvenile red snapper (Lutjanus campechanus) in the Gulf of Mexico and in the South Atlantic of weakfish (Cynoscion regalis) along with king and Spanish mackerel (Scomberomorus cavalla and S maculatus) in both fisheries had been cause for concern and it was thought that the incidental catch of these species in the shrimp trawl fisheries was limiting the resource available for fisheries directed at these species and the main aims of the programme were to reduce the capture of these species although, as can be seen below, other less commercially important species were more common in the incidental catch.

In the Gulf of Mexico Fish Shrimp trawl fishery was concluded that over 450 taxa were identified in the catch and average catch was about 27 kg/hour of trawling. The catch could be divided into three major components as shrimp 26%, other invertebrates 17% and finfish 67% giving a ratio of 5.25 bycatch to 1 of shrimp. This figure contrasts the figure of 10.3:1 given in Alverson et al for the Gulf of Mexico shrimp fishery.

The top ten species found in catch were as follows in Table 15

Table 15 - Top ten species found in Gulf of Mexico shrimp trawl catches

In the South Atlantic about 150 taxa were found in shrimp trawls with a catch rate of about 26 kg/hour. Shrimp made up 18%, other invertebrates 31% and finfish about 51% of the total catch. This gives a bycatch to other species ratio of about 4.5 to 1. The top ten species in the catch are listed as follows in Table 16.

9.5 Northern Prawn Fishery of Australia

The area of sea within Australia’s EEZ from Cape York in the east to Cape Talbot in the west is a rich area for capture of penaeid prawns. Known in Australia as the Northern Prawn Fishery (NPF) it yields quantities of the shoaling banana prawns (Penaeus merguensis) which involve little if any bycatch and quantities of the more disperse tiger prawns (P. esculentus and P. semisulcatus) which involve capture of considerable quantities of non-target fish or bycatch. A study by the Northern Territory Department of Primary Industry and Fisheries of bycatch between 1987 and 1992 (Pender et al 1992a) looked at the likely utilisation options for the common species in the bycatch. They concluded that 97% of the bycatch was discarded at sea with presently only valuable species being retained, these are detailed in Table 17.

Table 17 - Components of the bycatch in the northern prawn fishery retained onboard

Local Name Scientific grouping
Bugs (Shovel nosed lobsters) Thenus orientalis
Squids Loligo spp
Snappers Lutjanus spp
Emperors Lethrinus spp
Mackerels Scomberomorus spp
Cods Epinephelus spp
Sharks Carcharhinidae and Hemigaleidae

Of the discarded bycatch most was fish, with over 200 taxa recorded, belonging to 75 families. The major families of the discarded fish bycatch are given in Table 18 which shows that they are primarily of families which have a small size at maturity and were currently un-used in Australia.

Table 18 - Major families of fish discarded in the mixed species fishery in 1988

Local Name Scientific grouping Percentage of fish bycatch
Grinners Synodontidae


Threadfin/Monocle Breams Nemipteridae


Dollar Fish Leiognathidae


Trevallies, scads, queenfish Carangidae


Goatfish Mullidae


Leather jackets Monacanthidae


The studies identified a number of species with potential commercial value within the discarded catch. (Pender et al 1992b). The options for use included fish for direct human consumption, production of surimi, use as bait, fertilisers and animal feeds. The major city and capital of Northern Territories - Darwin, has groups of residents from Asian and other back grounds for whom some of the fish in the discarded bycatch are more familiar, than for Australians. A number of species in the bycatch were assessed for their acceptability by these groups and assessments of the viability of utilisation made. The data indicated that taking into account the population sizes and the amount of fish potentially available the following had market potential - trevallies, goatfish, threadfin breams and emperors. Available in smaller quantities but with higher demand from certain groups are species such as black pomfret, Bombay duck, whiting, tufted sole and octopus. The findings also indicated that generally any fish more than 13-15 cm in length could be acceptable for consumption.

The work also looked at the possibility of production of surimi, canned, dried and frozen products. It was concluded that, although feasible technically, there would be, at best, marginal profits on such enterprises.

Non-food use as bait, animal feeds and fertilisers were also investigated. Squids, pilchards, garfish, mullets and cuttlefish have potential as bait for anglers and commercial fishermen. The aquaculture of barramundi (Lates spp) requires supplies of raw fish. Three species in the bycatch were found particularly suitable as food for barramundi, with others which were tried being less acceptable and other species not eaten at all by barramundi. See Table 19.

Table 19 - Fish species preferences of Lates calcarifer brood stock




Pellona ditchela



Polydactylus multiradiatus



Setipinna tenuifilis



Thryssa hamiltonii



Thryssa setirostris



Harpadon transluscens



Saurida micropectoralis



Euristhmus lepturus

Tails only


Trichiurus lepturus



Apolectus niger



Chirocentrus dorab



Cynoglossus spp



Johnius vogleri



Johnius vogleri



Platycephalus spp



Priacanthus tayenus



*Scored from untouched (1) - most preferred (4)

This extensive study of the NPF bycatch utilisation possibilities concluded that "Although there is a large unused bycatch resource, making more use of it is fraught with difficulties as the potential large scale markets are not lucrative enough to support the costs of processing the product." This confirms the case that more often than not it is economics rather than technology that stands in the way of fuller utilisation of bycatch.

Recently it has been reported that trawlers operating in the Northern Territory Prawn fishery use hoppers on the deck of the vessel to assist in sorting of the catch. The prawns and fish are dumped on a grid above the hopper. The small animals fall into the hopper which is filled with sea water. The large ones are released over the side. The prawns sink to the bottom and land on a conveyor belt. These are brought out and transferred to a sorting conveyor belt. The fish swim around in the hopper until the prawns are sorted. The water is released and the fish are quickly moved along the conveyors back into the sea. No information is presently available regarding the eventual survival of the released fish. (S Kennelly Pers. comm.). A system of sorting in the water has also been reported as being used in the New South Wales prawn fishery where the mixed catch in the cod end of the trawl is emptied into a water tank, the live prawns settle at the bottom and the fish are taken from the top and floated off.

9.6 South East Asia

The move towards the use of bycatch species for the production of traditional food products in South East Asia, such as fish balls, was catalysed largely by the South East Asia Fisheries Development Centre, Marine Fisheries Research Department (MFRD) in Singapore. Through a series of laboratory based experiments it was ascertained that the meat of certain species of bycatch fish had the right gelling and protein properties to produce fish jelly products such as fish balls for local consumption and had potential for the production of surimi as a potential export. The MFRD has been running training courses and publicity campaigns for fish ball manufacturers in S E Asia for a number of years now and bycatch is now a supplementary source of raw material for the industry. The species involved include threadfin breams, croakers, big eye snapper and barracuda which are found in bycatches from the shrimp trawlers in the region and other parts of the world.

9.6.1 Thailand

Suwanrangsi (1988) reported the development of a range of products from bycatch from both fish and shrimp trawlers in Thailand, with the assistance/collaboration of the SEAFDEC and others. Dominant among the species caught are threadfin breams (Nemipteridae) goat fish (Mullidae), trevallies (Selaroides), flatheads (Platycephalus) and bigeye (Priacanthus) which as can be seen from Table 14 are common in other fisheries as well. In looking for means of using these potentially valuable fish groups it was necessary to assist in improving on-board handling systems so that improved quality raw material was available. This involved work on upgrading handling systems using chilled sea water and the transhipment at sea on a daily basis to ensure the raw material of adequate quality for processing and eventual human consumption.

Threadfin bream, and other species were found to have suitable gelling properties for the production of surimi products and the number of surimi plants in Thailand and the exports of surimi from Thailand to Japan increased dramatically during the 1980’s. In addition bycatch species have been increasingly used for the production of locally consumed products such as fish balls - species which have been demonstrated to be particularly useful in this regard are again, threadfin bream, tongue sole, bigeye, goat fish, glass pony fish and flathead and these species are increasingly being used to supplement and replace the more traditional species (barracuda, sea eel and sole) which because they can be used for export products such as surimi are in greater demand. Several other products have been developed such as noodles, sausages and seasoned minces using bycatch species. One particular item that has found both export and local marketing success is fish satay made from lizard fish (Saurida spp). A report prepared for FAO (Kungsawan 1996) maintains that very little discarding now takes place at sea in the Thai shrimp industry. The non-shrimp catch can be divided into specimens which have immediate human consumption value, those that are processed before consumption, those which are juveniles of commercially important species and "true trash fish". It appears therefore that a whole new sub set of activities has now developed in Thailand specifically to deal with non-target organisms from the shrimp industry. The paper by Kungsawan suggests that over 1.2 million tons of trash fish was made into fish meal in 1992 contributing substantially to the country’s fish meal requirements. Using the conversion factor suggested in the paper this is likely to have produced about 266,000 tonnes of meal. The FAO figures for imports of fish meal to Thailand for 1992 are given as nearly 67,000 tonnes, valued at just over 49 million US $ (FAO 1996c). This suggests that locally produced fish meal from shrimp trawling makes a substantial contribution to the nations fish meal requirements. As well as over 100 land based fish meal plants some processing boats for fish meal are also reported to be operating at sea and purchasing trash fish from boats at sea.

The trash fish component of the catch which is called "true trash" and made into fish meal is made up a number of species the predominance of which depends on the fishing methods and areas. The most common families/groups are given in Table 20 below.

Table 20 - Main species in the "true trash" component

Species group

Rough proportions in trash



Trash crab











Small to medium


Small to medium



Daya spp








Bragmaceros spp



Very small

Pentaprion longimanus

Very small

Siganus spp

Very small

Other at-sea operations for use of bycatch include the preliminary salting of anchovies for fish sauce manufacture, the boiling of anchovies, prior to land based drying to make dried boiled anchovies for export to Malaysia and the salting of some other varieties of fish, such as king mackerel for production of high quality/value products for both domestic and export markets.

The rest of the catch will be sorted into fish suitable for human consumption including small specimens which would be classified as bycatch. In the industry large fish of commercially species are not considered bycatch and are part of the normal fish catch, entering the human food chain directly as fresh fish on local markets. Small species of fish such as threadfin breams, monocle breams and croaker, are especially sorted from the rest for production of surimi type products and fish balls. Local traditional products such as salted dried fish, fish sauce, fermented fish, shrimp paste and dried cephalopods are also made from bycatch. The main components within the bycatch not categorised as trash are shown in Table 21.

Table 21 - Main commercial fish species caught as juveniles in the Thai shrimp bycatch

Common Name Scientific Name
Indian mackerel Rastrelliger kanagurta
Lizard fish Saurida isarankurai
Lizard fish S. undosquamis
Lizard fish S. elongata
Threadfin bream Nemipterus hexodon
Threadfin bream N. mesoprion
Purple spot bigeye Priacanthus tayenus
One-finlet scad Atule mate
Yellowstripe scad Selaroides leptolepis
Monocle bream Scolopsis teaeniopterus
Tonguesole Cynoglossus spp
Flathead fish Platycephalus spp
Deep bodied trevally Atule kalla

9.6.2 Malaysia

The species make up of catches from trawlers operating in waters near Kuala Kedah on the west coast of peninsular Malaysia has been reported by Abd. Haris Hilmi (1997). He reports that there is no discarding at sea from the small trawlers fishing from Kuala Kedah which operate on a one day per trip basis. Landings obviously vary but, averaged during the survey about 500 kg per day trip. Of this 330 kg (66%) was classified as "trash fish" and was "sent to the nearby fishmeal factory". Details of species classified as trash fish are given in Table 22.

Table 22 - Trash fish in Malaysian shrimp trawls

Dominant in the fish sent for fish meal are small Rastrelliger spp, Apogon spp, Secutor spp during spring tide fishing and during the neap tide fishing Stolephorus andhraensis made up over 40% of the trash fish.

In addition to the species listed above some small prawns of the target species were also included in the trash and as can be seen some fish which are also included in Table 23 below for marketing and sale. The criteria for sale as human food or conversion to meal is based on size, small specimens being sent for fish meal production the larger ones for human consumption either fresh or dried.

Table 23 - Major commercial species caught in Malaysian shrimp trawls

    Major group Scientific Name Common name
      Penaeus merguiensis Banana prawn
      Metapenaeus lysianassa  
      Metapenaeus dobsoni  
      Metapenaeus affinis  
    Pelagic Fish    
      Rastrelliger brachysoma Short mackerel
      Sardinella fimbriata Fringescale sardine
      Chirocentrus dorab Wolf herring
      Scomberomorus spp Spanish mackerel
      Atule mate Yellowtail scad
      Stolephorus heterolobus Shorthead anchovy
      Pampus argentus Silver pomfret
    Demersal Fish    
      Atropus atropus Cleftbelly trevally
      Cynoglossus lingua Long tongue sole
      Dasyatis spp Stingrays
      Muraenesox cinereus Conger eel
      Nibea soldadu Soldier croaker
      Pennahia macrocephalus Greyfin croaker
      Nemipterus japonicus Japanese threadfin bream
      Nemipterus hexodon Ornate threadfin bream
      Otolithes ruber Tiger-toothed croaker
      Anodontostoma chacunda Chacunda gizzard shad
      Loligo duvauceli Squid
      Sepia aculeata Cuttlefish
      Sepioteuthis lessoniana Squid
      Sepiella inermis Cuttlefish
      Carybdis cruciata Swimming crab

    As reported by Chee (1996) there are now specific value added marketing opportunities for some of the previously discarded trawl bycatch species in Malaysia as follows:

Table 24 - Uses for some Malaysian trash fish

    Species Use
    Croakers Salted/Dried
    Mullids Barbecue/Snack foods
    Mantid shrimp & Shovel nose lobsters Sold fresh
    Synodontids, bulleye Fish balls

9.6.3 Myanmar

In Myanmar, U Khum Mg Aye (1995) reported that some bycatch from the shrimp trawlers along the Rakhine coast is collected by local fishing craft at sea and brought for sale at local markets although the majority was discarded at sea. The report suggests that between 10 and 20% of the bycatch had value as human food on local markets with the rest being sold as animal feed. The fish involved in the bycatch belonged to the following families;

Pomadasyidae, Sciaenidae, Synodontidae, Nemipteridae, Trichiuridae, Clupeidae, Carangidae, Scombridae, Mullidae, Ariidae, Dasyatidae, Lutjanidae, Serrenidae, Muraenesocidae, Stromatidae, Loligonidae, Polynemidae.

9.6.4 South East Asia general

From the above it would appear that there are markets in South East Asia for many species caught as bycatch in shrimp trawling particularly the following species groups:

    Flatheads (Platycephalus)

    Threadfin breams (Nemipteridae)

    Bigeye (Priacanthus)

    Goat fish (Mullidae)

    Tongue sole (Cynoglossidae)

    Croakers (Sciaenidae)

    Barracuda (Sphyraenidae)

    Trevallies (Selaroides)

    Glass pony fish (Leiognathidae)

Referring to the Table 14 above it can be seen that some of these species are common throughout the world of shrimp bycatch and the literature and experience suggests that although they are utilised to advantage in some Asian countries this is not necessarily so in other regions. The profitability of the main activity of catching shrimps has perhaps declined and the added income from marketing selected fish from the catch has become more attractive. This trend was noted even in the early 1980’s by Saisithi (1982) where there was in Thailand, at least, a move from use of bycatch for animal feeding towards human consumption - this trend has been accelerated in recent years.

9.7 South Asia

9.7.1 India

Studies on the options for improved use of bycatch form shrimp trawlers in India have been made which suggest that, as might be expected in such a vast and diverse country, the socio-economic and marketing differences affect utilisation scenarios in different parts.

In Gujarat on the north west coast of India for instance virtually all bycatch from the local prawn trawlers is used, (Bostock 1987). The majority is dried either with or without salt and depending on species and quality of raw material will be used for human consumption or for poultry feeds. More recently the processors sort out larger specimens from the bycatch which will be able to be sold fresh on the local market. They also now sort the bycatch by species to produce single species dried products which can be sold at higher prices than mixed species batches. The main sorted species are jewfish (Sciaenids), pomfret and ribbon fish. (Personal observation)

The situation on the east coast of India however is more varied it seems. (Bostock and Ryder 1995) There are a number basic types of trawling operation in the Bay of Bengal for shrimp varying in size, fishing grounds and means of onboard preservation. These differences influence the way in which the non-shrimp catch is used. The freezer trawlers tend to retain all "quality fish" which is bulk frozen in pounds and assuming storage space is available on board the small miscellaneous fish may be bulk frozen in the cold rooms during the last few days of a voyage. The government owned freezer trawlers sell their frozen bycatch through a pre-arranged system to traders who transport it to Howrah Market in Calcutta.

With the smaller craft the landed quantities depend primarily on the length of trip and the availability of excess ice (after the preservation of the target shrimp), salt and deck space for sorting and /or drying of certain species such as anchovy and jewfish.

The most common reason given for not retaining more of the bycatch is the difference in value between shrimp and the non-shrimp. However, there are also considerable differences between the value of different species within the fish bycatch as is illustrated in Table 25. This data illustrates the influence that size can have on value with Polynemus and Sciaenids for instance being classed as high value above a certain size but as trash below that size. This means that fishermen will tend to sort out fish of particular species and sizes for separate sale from others which they may either discard at sea or land but sell in bulk for production of animal feeds or fertiliser.

Table 25 - Average percentage composition of fish landings - Nov. 1990 to Mar. 1991

    Category of bycatch and group

    Average quay-side price (Rs/kg)

    Approx. size (cm)

    % of landings

    Small miscellaneous fish      




























    Lizard fish

    2.5 - 5















    Polynemus spp




    Ribbon Fishes












    High Value Fish      
















    Polynemus spp
















    Flat fishes












    Source: Bay of Bengal Programme (1991), cited in Bostock and Ryder (1995)

    Rs = Rupee 25 = US$ 1 (at the time of publication)

9.8 Preservation before landing

One of the primary reasons why shrimp bycatch is not used more extensively is that in order for it to be landed in fresh enough condition to be of use it needs to be preserved and stored on board the catching vessel, probably for some days (on multi-day fishing trips), before landing. The costs in terms of storage space on board, means of preservation (ice or refrigeration) and the time and effort of the crew in undertaking the tasks involved generally out-weigh the first sale value of the catch.

Investigations have been made in a number of situations on ways to unburden the catching vessel of the bycatch and the associated costs. These have involved the possibility of mother ships and carrier vessels collecting fish direct from the trawlers or from containers of bycatch jettisoned into the sea for instance. The costs involved in setting up and running such formalised, often government run and instigated, systems, however, have often been found to far out-weigh the value of the bycatch itself. More success has been found with the involvement of small craft where the capital and running costs are less and the owners and operators have stepped in to take advantage of a raw material which costs little. This activity has appeared as a follow on from fishing in some instances. Small-scale fishermen in coastal waters finding it more and more difficult to make a living from fish capture have turned, using their existing tools and skills (boats and seamanship) to collecting unwanted catch from shrimp trawlers. It is ironic, perhaps, that the use of shrimp trawlers in coastal waters has sometimes been blamed for the disruption of traditional fishing patterns by small-scale fishermen and yet that same activity may be alleviating some of the problems it has created by giving those same fishermen alternative income generating opportunities.

The problems of retaining fish on board are as follows:

  • Sorting problems onboard
  • Time taken for unloading bycatch in port
  • Prolonged turn round in port reduces the operational time of the vessel
  • Limited storage space on board
  • Limited preservation facilities on board
  • Possible contamination of shrimp

It would appear that transferring the fish to carrier vessels for subsequent discharge at port overcomes these problems, however, transfer at sea brings with it it’s own problems:

  • Physical difficulties of transfer between vessels
  • Rough weather making it difficult and unpredictable
  • Possibility of the crew off loading not just bycatch but also more valuable catch makes it unattractive for many vessels owners/operators
  • Problems with the catching vessels and the collecting vessels locating one another at sea

However, even if these problems can be overcome simply bringing the fish to shore is not generally enough. In order for sustainable arrangements to be made for collection of bycatch at sea there appear therefore to be some important prerequisites. These might be listed as follows:

  • Suitable collector vessels
  • Willing crews
  • Favourable sea conditions
  • Agreement with the vessel owners
  • Marketing opportunities for the bycatch

There are, however, a number of cases where transfer at sea has helped to promote the use of fish that would otherwise be wasted.

9.8.1 Bay of Bengal

Fish collection happens with Indian vessels operating in the Bay of Bengal, but in an informal and opportunistic manner. As suggested above some of the mitigating circumstances which appear to make informal collection such as this more likely are as follows:

  • Trawlers working relatively close to shore.
  • Poor fishing opportunities for traditional fishermen who use their normal boats to collect bycatch instead
  • Favourable weather conditions.

The informal arrangements seem to be often of little advantage to the crew of the trawling vessel since as reported by Kulberg (1989) in one observed exchange in the Bay of Bengal the crew of the vessel received some cigarettes for the fish but no cash payment. In other exchanges fresh food is exchanged for the bycatch. On the other hand there is little disadvantage to the crew of the vessel since they would be involved in disposing of the fish over the side in any case. The main point that is apparent from the information available on the situation in the Bay of Bengal is that the transfer of fish at sea is generally not sanctioned by the vessel owners, who fear the clandestine transfer of more valuable catch and therefore loss of revenue.

9.8.2 Gulf of Thailand

In the Gulf of Thailand, Kungsuwan (1996) reports that collection at sea now normally happens with vessels making longer trips. The company which owns the vessel arranges to rendezvous at sea primarily to provide provisions such as ice and food and for the collection of the target catch, however if space allows bycatch will also be transferred at sea and brought to shore for marketing. In the Gulf of Thailand there are also vessels which produce fish meal at sea from waste fish and fish is transferred to them from fishing vessels for processing.

9.8.3 Mozambique

In Mozambique a system is now operating whereby small scale, artisanal fishermen are using their boats to collect bycatch from shrimp trawlers, negotiating for a share of the bycatch on a barter basis and in competition with a system of collector vessels that had been set up by government with foreign aid assistance, (Kelleher and Musa 1995). The aid project had adopted a strategy for establishment of five collection centres where fish would be salted and dried or packed for fresh distribution along the coast of Mozambique. These centres were to be serviced by collector boats from trawlers to shore for raw fish and transport vessels for transport of product from the collection centres to major cities. The project’s experiences were, however, not encouraging. In the first few months of operation the production targets were only being fulfilled to about 10% and the over capitalisation in boats and equipment was proving problematical. As has been suggested above however the project provided a spur to entrepreneurs to enter the system and utilising a less capital intensive and simpler mechanism for use of the resource. The uptake in Mozambique has been assisted by the shortage of alternative protein supplies on the local market because of years of civil unrest. The bycatch products have centred around traditional food items in the diet such as dried/salted and fresh fish rather than development of new products.

The species which appear with most frequency in the bycatch in Mozambique are shown in Table 26.

Table 26 - Common species in Mozambique bycatch

    Scientific Name English/local Name
    Hilsa kelee Kelee shad
    Thryssa vitrirostris Orangemouth anchovy
    Johnius dussumieri Sin croaker
    Otolithes ruber  
    Trichiurus lepturus Hairtail
    Arius dussumieri Blacktip sea catfish
    Cynoglossus spp Sole
    Pellona ditchella Indian pellona
    Upeneus sulphureus Silver goatfish
    Upeneus taeniopterus Fin stripe goatfish
    Terapon theraps Largescaled terapon
    Leiognathus equulus Common ponyfish
    Polynemus sextarius Blackspot threadfin
    Gazza minuta Toothed ponyfish
    Sillago sihama Silver silago
    Sepia spp Cuttlefish
    Pomadasys maculatum Saddle grunt
      Small prawns

9.8.4 Madagascar

In Madagascar an aid assisted programme for the collection at sea and the use of bycatch from prawn trawling has been reported by Rakotondrasoa (1995). The bycatch was divided into three categories depending on the end use to which it could be put. First choice fish with the highest value could be used for fresh distribution into the hotel and restaurant trade as well as to higher income consumers. The species concerned are shown in Table 27.

Table 27 - First grade fish for hotel and restaurant trade in Malagasy bycatch

    Scientific name English name
    Sphyreana spp Barracuda
    Scomberomorus commersoni Narrow-barred Spanish mackerel
    Psettodes erumei Indian spiny turbot
    Otolithes ruber Tiger-toothed croaker
    Nemipterus bleekeri Threadfin bream

There is a second category of fish species which is sold to the less affluent section of the population, consisting of the species listed in Table 28.

Table 28 - Second grade fish in Malagasy bycatch

    Scientific name English name
    Leiognathus spp Ponyfishes
    Decapterus russelli Indian scad
    Dussumieria acuta Rainbow sardine
    Rastrelliger kanagurta Indian mackerel
    Terapon spp Terapon
    Upeneus vittatus Goatfish

The third group of species which is used as animal feeds includes:

Saurida tumbil (Greater lizardfish)

Chirocentrus dorab (Wolf herring)

Small mixed fish

Mixed crabs and other crustacea

The programme was geared towards producing a fully integrated system for collecting the bycatch from the prawn trawlers at sea, transferring it to shore and processing of the fish for both human and animal feeds.

9.8.5 Tanzania

The composition of bycatch and potential discards in the Tanzanian shrimp fishery is similar to elsewhere. Mgawe (1995) lists the species in Table 29 as being most important in the composition of the fish that is landed. Fish that is discarded at sea is not included. Although species of fish takes priority over size, fish which is retained for sale is generally of 50 gms or above, with smaller fish being thrown overboard - discarded what ever the species.

Table 29 - Most frequently observed species in the bycatch in Tanzania

    Scientific name Local/English name
    Leiognathids Pony fish
    Thryssa spp Anchovy
    Trichiurus spp Hairtail
    Chirocentrus spp Wolf herring
    Otolithes spp Tiger tooth croaker
    Arius spp Catfish
    Cephalopoda Cuttlefish/squids
    Mugil spp Mullet
    Holothuria Sea cucumber

The collection of bycatch and its utilisation has evolved over recent years and is now a viable business for a number of scales of operation. This has been catalysed, partly, by government which now requires that a fisheries officer accompanies the fishing boats and that trawl fishing should stop at 18:00 hrs to allow for collection of bycatch. The amount of bycatch landed is also a significant factor in the granting of renewal of the annual fishing licence. These measures have ensured that trawler owners now preserve a reasonable amount of bycatch.

Mgawe suggests that there are no marketing problems for the bycatch and that there is room for increased utilisation. He suggests that legalising the present undercover sales at sea, increased communications between the various centres involved and adherence to the government regulations which restrict fishing after 18:00 hrs, thus allowing time for off loading bycatch at the close of the days fishing, would stimulate the trade still further.

9.8. 6 Gambia

In Gambia an informal arrangement has arisen whereby fishermen who have been displaced and initially disadvantaged by the presence of shrimp trawlers now make a business of collecting bycatch from the trawlers and selling it through various outlets on shore. These collectors have arrangements with the crews and captains of the vessels and most fish is exchanged for food stuffs rather than cash although some of the more valuable fish may be purchased for money. This trade is not sanctioned by the vessels’ owners because of the risk of sale of target species but there is little that can be done to stop it. The demand for the products available as bycatch from the trawlers has come from a number of quarters which has encouraged the trade. Shrimp and other "good quality" fish are sold to hotels and restaurants by prior arrangement, sole and cuttlefish are of particular interest to some middlemen and most of the fin fish catch is sold direct to consumers or through middlemen on the beach. (Jallow 1995) The species present in the catch as listed by Jallow are given in Table 30 below.

Table 30 - Species in shrimp trawler catch in Gambia

    Scientific name English name
    Pseudotolithus typus Long neck croaker
    Pseudotolithus brachynathus Law croaker
    Pseudotolithus senegalensis Cassava croaker
    Fonticulus elongatus Bobo croaker
    Plectorhyncus mediterraneus Rubberlip grunt
    Pomadasys jubelini Sompat grunt
    Epinephelus aeneus White grouper
    Epinephelus guaza Dusky grouper
    Polydactylus quadrifilis Giant African threadfin
    Galeoides decadactylus Lesser African threadfin
    Sepia spp Cuttlefish
    Arius latiscutatus Rough head sea catfish
    Arius heudeloti Smooth mouth sea catfish
    Sphyraena spp Barracuda
    Penaeus notialis Shrimps
    Drepane africana African sickle fish
    Cynoglossus senegalensis Sole fish
    Cybium spp Snail

Data provided by Jallow suggests that of the non-shrimp catch the African threadfins, croakers, grunts, sole fish and African sickle fish make up the major part of the bycatch. Barracuda and cuttle fish are relatively rare and seasonal. The Cybium spp have become the subject of specialised processors being fermented and exported to Senegal where they are in high demand.

9.8.7 Cameroon

In Cameroon the transfer of fish at sea is illegal (Eyabi-Eyabi 1995) however local fishermen find that collecting fish from trawlers at sea is more lucrative than going fishing and some practice this trade on a regular basis. It is estimated that about 1,000 tonnes of bycatch fish were landed per year on the beaches and is sold in mixed batches of both marketable and unmarketable fish at prices agreed between the ex fishermen and the crew of the trawler. Resale value at the beach can be two or three times the price that was paid to the trawler crew, although some fish will be thrown out as unsellable. The most common marketable fish which are either sold fresh, smoke/dried, boiled, fried, roasted or grilled are shown in Table 31

Table 31 - Marketable fish in bycatch in Cameroon

    Scientific name English name
    Ethmalosa spp Bonga shad
    Sardinella spp Sardinella
    Pellonula vorax Bigtoothed pellonula
    Brachydeuterus auritus Bigeye grunt
    Ilisha africana African ilisha

9.8.8 Cuba

In Cuba the government have set up a system for recovery of bycatch from their domestic fleet (Garcia-Rodriquez 1995). The difficulties of vessel to vessel transfer of bycatch at sea which can be affected by weather conditions and problems of location at sea have been overcome by the establishment of receiving centres at sea. These are located at the fishing grounds and are used only when the fishing fleet is fishing away from shore and not landing at shore based plants on a daily basis.

The trawlers after each haul sort the catch into three components before onboard preservation.

  • Shrimps
  • Fish from the bycatch for human consumption
  • Fish from the bycatch for animal feed production

The trawlers off-load their catch at the receiving centres on a daily basis, where it is further iced and then transferred to carrier vessels for transport to shore based processing plants. This system allows good quality bycatch for human consumption to be landed for various products. The trawlers, collecting vessels, receiver centres and the industrial plants are all government owned making implementation and control of such a system relatively straight forward. There are requirements that skippers land predetermined quantities and quality of bycatch at the centres and if these are exceeded then crews get bonuses. Recent evidence suggests that all the edible bycatch is now utilised. Bycatch can include up to 30% jelly fish, star fish, sponges etc. which are inedible and discarded but the rest is either sold fresh after sorting by species or made into fish minces and pulps for freezing and human food. (F Teutscher Pers comm.)

A list of the main species used in Cuba for human consumption from the bycatch are shown in Table 32

Table 32 - Main species used for human consumption in Cuban bycatch

    Scientific name English Name
    Lepophidium graellsi Emerald
    Lutjanus synagris Lane snapper
    Micropogonias furnieri Croaker
    Diplectrum formosum Sand perch
    Synodontus spp. Lizard
    Dasyastis spp. Rays
    Callinectes sapidus Blue crab
    Squilla Mantis shrimp
    Panulirus argus Spiny lobster
    Loligo pealei Squid
    Amusium laurentis Clams
    Laevicardium laevigatus  

9.8.9 Suriname

It appears that most of the bycatch from shrimp trawling in Suriname is discarded at sea. Lieveld (1995) reported that some of the larger specimens of favourable fish were kept but that most of the fish landed along with the shrimp was caught during the return voyage to port in shallow waters and therefore do not necessarily represent the species that are discarded at sea during normal operations. These species are shown in Table 33.

Table 33 - Species landed and utilised from shrimp bycatch in Suriname


    Percentage of landing

    English name of species
    Arius parkeri


    Gillbacker sea catfish
    Arius proops


    Crucifix sea catfish
    Bagre spp


    Sea catfish
    Other Ariidae


    Cynoscion virescens


    Green weakfish
    Macrodon anclyodon


    King weakfish
    Micropogonias furnieri


    Whitemouth croaker
    Nebris microps


    Smalleye croaker
    Other Sciaenidae


    Caranx hippos


    Crevalle jack




    Rachycentron canadus


    Batrachoides surinamansis


    Pacuma toadfish
    Xiphopenaeus kroyeri



The capture of some at least of this fish is made deliberately by the crew as they gain direct income from its sale. The catfish is generally smoked whereas the other fish species may be smoked, sold fresh (as fillets or steaks) or salted. Rachycentron canadus and sharks are salted. The quality of the fish at landing is affected by the onboard handling, generally the shrimp are sorted by hand from the catch first. The fish to be kept are then sorted, washed and place in the onboard freezer. The indications are that the quality of the fish is not high but can be sold in local markets fresh. Once unloaded from the trawlers storage in ice during onward marketing is normal.

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