A Review of Bycatch and Discard Issue Toward Solution

K. Tsukamoto, T. Kawamura, T. Takeuchi, T. D. Beard, Jr. and M. J. Kaiser, eds. Fisheries for Global Welfare and Environment, 5th World Fisheries Congress 2008, pp. 169–180. © by TERRAPUB 2008. A Review of Bycatch and Discard Issue Toward Solution Tatsuro Matsuoka Faculty of Fisheries Kagoshima University Kagoshima, Japan E-mail: [email protected] A total of 27 million tons and a revised value of 6.8 million tons of global discards have been estimated, however, there is still no reliable discard estimation globally. The reason is the fuddled definitions of the terms used in this field such as bycatch and discards and methodological mystification in their applications. Despite the concerns, factual problems of discards have been limitedly discussed scientifically. The survival possibility for discarded organisms is a major subject, where high survival rates are found for matured indi- viduals and large species of finfishes and crustaceans but low, for juveniles and small finfish species. The subsequent energy flow after discards is also a large research topic. Externalisation of discards by seabirds on surface and scavenging on seabed do not support the hypothesis of enrichment of surface water by nutrients from discards. Approaches toward solutions to discards include exclusion of bycatches underwater by improvement in fishing technology such as selectivity enhancement and development of bycatch exclusion devices and promotion of landing of discards otherwise. A simple analysis on the commonness between bycatch and discards is encouraged in realistic approach toward exclusion of juveniles of useful species and promotion of landing of unutilised species. KEYWORDS bycatch; discard; incidental catch; capture fishery; resource; management; mortality; survival bycatch and discards of fisheries organisms 1. Introduction has been actively conducted around the world after that FAO promoted conversion Discarding bycatch began drawing attention from discards to utilisation in 1982 (FAO as the most serious wastage in capture fish- 1982). It has become an international issue eries against rational utilisation of marine in fisheries management since the estimation resources during the 1970’s. Researches on of global discards by FAO Technical Paper 170 T. MATSUOKA 339 (Alverson et al. 1994) and adoption of tained in part, while the remainder is dis- FAO Code of Conduct for Responsible Fish- carded. Retention and landing are almost eries in 1995, where bycatch and discards synonymous in the case of industrial fisher- were dealt repeatedly. A variety of researches ies, however, self-consumption in retention have been conducted, such as in situ surveys seldom appears in landing statistics. The of discard practices, development of tech- definition of discard as those non-retained nology to reduce bycatch and discards, and in catch is almost consensus, however, there studies on the consequences of discarding in are still different opinions such that release the ecosystem and formulation of the scien- in sport fishing or safe returning to the sea tific basis approaching through sensory and after friendly sorting onboard should be ex- behaviour of aquatic organisms. The orien- cluded. Discard also takes place on land, tation toward these researches during the mid which is not included in the landing. 1980’s was conjectured to be a reflection of, Despite the title of this paper, bycatch is at least in part, the world-wide trends toward hardly defined scientifically. The definition conservation of aquatic environment and re- of bycatch is different among countries and sources those days. It is also a character of researchers (Alverson et al. 1994), and com- this issue that efforts have been devoted to mon basis is hardly pertained. Alverson used the estimation of the discard amount in par a concept of a set of target catch and bycatch, with the researches toward solutions, because however, target catch is subjective and it is FAO Technical Paper 339 reported an esti- not a realistic approach to identify a single mate of a large amount of discards in regions. target species and to define all the others as An increasing number of case studies are still bycatch. According to this definition, there being conducted in the 2000’s globally, in- is a landed bycatch, which could be referred cluding those in the third world countries. to as by-products. The concept is hardly ap- The bycatch issue involves those of both plicable to multi-species fisheries which are fisheries organisms such as finfishes, crus- prevailing over Asian region and tropical taceans, etc. and non-fisheries animals which waters. An enormous effort has been, there- are not aimed in fishing, such as marine fore, devoted by e.g. SEAFDEC to define mammals, marine reptiles and seabirds. The the terms applicable in Asian fisheries latter is referred to as an incidental catch, (SEAFDEC 1998). This paper temporalily although the term of bycatch implies both. defines bycatch as is the irrational catch The bycatch and discard issue tends to refer rather than the catch of species, sizes and only to the former. Two groups of animals sex acceptable in resource conservation and have different characters both in implications management. in the fisheries management and from the viewpoint of the required technology toward 3. Estimation of Bycatch and solutions, therefore, it is difficult to deal with Discard Amounts in one context. This paper deals with mainly the bycatch and discards of fisheries organ- The amount of discards was first estimated isms and reviews the historical progress in in the prawn trawl fishery (Slavin 1982). A the issue. total of 5 million tons of annual discards in the world prawn trawl fishery was estimated 2. Definition of Terms on the basis of the discard ratios against the catch of prawns, which are usually 5 to 10, Definitions of the terms used in this field are and are multiplied by a total production of chaotic. Catch is defined as those hauled up prawns (a discard ratio and its application once onto deck with fishing gear, then re- will be explained in detail later). This method Bychatch and discard issue toward solution 171 Table 1. Global and regional discards estimated in 1994. Region No. Nominal regions Discards (1000MT) (%) 61 Northwest Pacific 9,132 33.8 27 Northeast Atlantic 3,671 13.6 71 Central-west Pacific 2,777 10.3 87 Southeast Pacific 2,602 9.6 31 Central-west Atlantic 1,601 5.9 51 West Indian 1,471 5.4 67 Northeast Pacific 925 3.4 41 Southwest Atlantic 803 3.0 57 East Indian 802 3.0 77 Central-east Pacific 767 2.8 Others 2,461 9.1 Total 27,012 100 *Tabulated from Alverson (1994) was applicable only because the anticipated Table 2. Estimation of global and national prawns and unwanted finfishes so-called as discards revised in 2005. bycatch are distinctively segregated in this Countries (Asia) Discards (1000MT) (%) sector. The estimation of discards in later researches was unconsciously affected by Cambodia 0.0 0.0 this method. China 74.3 1.1 Indonesia 270.4 4.0 FAO Fisheries Technical Paper 339 es- Japan 918.4 13.5 timated 27 million tons of global discards Korea 1.0 0.0 annually (Alverson et al. 1994). Though dis- Malaysia 10.4 0.2 card estimates by country were concealed, Myanmar 27.4 0.4 it was presented that 47% of the global dis- North Korea 1.1 0.0 cards occurred in Asian waters, in particu- Philippines 7.5 0.1 lar, 9.13 million tons in Region-61, or North- Thailand 27.8 0.4 Viet Nam 17.8 0.3 west Pacific, which was unrealistically large Others 5463.1 80.1 (Table 1). Responding to the criticisms, FAO convened an expert consultation meeting Global Total 6819.2 100.0 (FAO 1996). It was revealed that Paper 339 *Tabulated from Kelleher (2005) had methodological weakness which did not take the landings as non-target catches into account and fell into over-estimation of discards (Matsuoka 1996), although it was not tries and less than that for North Korea, de- described in the conclusion of the meeting spite no scientific data available for this criti- (FAO 1996). cism (Table 2). There is still no reliable esti- A revised estimation of global discards mation of global discards even nowadays. of 6.8 million tons was publicised by FAO There are several reasons of the confu- (Kelleher 2005). This report included unac- sion in discard estimation. One is the fud- ceptably unnatural assessments, for exam- dled definitions of bycatch and discards as ple, that the discard amount estimated for explained above. The other is that less logi- Korea was the smallest among Asian coun- cal consideration was given to the estimation 172 T. MATSUOKA methodology, perhaps, because it is too sim- 1 K ple for scientific studies. In order for discard q = d ()3 K ∑ k estimation, a discard ratio r in a certain fish- k=1 ing sector is found by field survey as Eq. (1) (Alverson et al. 1994; Matsuoka 1999) where DqE= ⋅ ()4 dk and ck are discard and landing amounts at the k-th sampling in K times. The total amount of discards D in the concerned sec- 4. True Problems of Bycatch and tor is estimated as Eq. (2), with the total Discards amount of landing C in the sector, which is usually available in landing statistics. How- Despite the prevailing concerns to bycatch ever, a variety of discard ratios are definable, and discards with emotional warnings some- because the landing of either summed spe- times, there had been a few scientific dis- cies, target species, or an individual species cussions on what are the problems in reality. is adoptable as a denominator.

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