Discards in Japanese marine capture fisheries and their estimation

By catch focused here is incidental catch to be discarded at sea and those utilised is dealt little. This is because, as widely stated, by catch is not necessarily a negative practice as there are many fisheries which are feasible with by catch in addition to the principal species. It is important to segregate by catch and discard issues. It may provoke unnecessary and unproductive contradiction, if by catch as a whole is dealt in the same line with discards. This report firstly overviews the structure of the fishing industry of Japan and its statistics in view of its sectors and landing. This aims at illustrating its basic characters and changes for the recent years. Secondly, the report summarises available information on discards from a sector to sector. It estimates, then, the amounts of discards by individual sectors and, subsequently, the total discard by the Japanese marine capture fishery as a whole. The last part of the report discusses improvement of methodology in discard researches. In this report, only publicised data were utilised for discard estimation with exceptions of those recorded by the author or the author's group. Discard ratios were either directly adopted or secondarily evaluated from those records

Methodology to estimate bycatch and discards

FAO Fisheries Technical Paper 339 (1994) provided the first estimation of global bycatch and discards, however, the estimated discards of 27 million tons have been abolished at FAO Consultation Meeting in Tokyo (1996). This was attributed to application of its discard ratios, total discard/landing of target species, to total landing with little respect to multi-species fisheries, which resulted in over-estimates of fishing effort and, consequently, discards. In order to determine the methodology for estimation of discards in multi-species fisheries in Asia, it is important to take into account; (1) it is difficult to segregate target and bycatch species, and (2) discards of species are not necessarily correlated to landing of single species positively. Therefore, the realistic approach is to define discard ratios as total discard/total landing and species discard ratios, if necessary, also against total landing in each fishing sector. Several methods to estimate bycatch and discards have been proposed recently with increasing concern to by-catch and discard issues, while information of by-catch in multi-species fisheries is scarce. Researches on characteristic discards in multi-species fisheries in the Region must be promoted for the regional fisheries to contribute in the international fisheries management

Temporal Changes in a Tropical Nekton Assemblage and Performance of a Prawn Selective Gear

The temporal variation of components of a moderately diverse (H=1.46) tropical estuarine fish assemblage (long. 146°30'E, lat. 8°45'S) was directed by salinities that had been determined by local oceanographic and probably topographic conditions. For this assemblage, two types of intrayear component profiles are predicted. Pooled data (1988-91) reveal a large component of regular/resident species (43%) in an assemblage which has been under a narrow temperature regime «5T). These results facilitate a discussion on the relevance and usefulness of three hypotheses often cited in studies concerning species diversity and component characteristics of the subtropical/tropical coastal nonreef fish assemblages. Manifestations of the assemblage are reflected in catch composition and weights of 39 trials conducted for a selective prawning gear whose performance in bycatch reduction, mainly for finfishes, is judged by an index, E, we have previously proposed. This gear is capable of harvesting the prawn while conserving the demersal fish. Behavioral responses to netting of the prawns and the finfishes, especially the nearshore surface schoolers such as leiognathids, are discussed from several points of view. An adaptation in terms of group selection for leiognathids of their locking mechanism of median fin spines has been interpreted. For the purpose of bycatch reduction or E enhancement, suggestions for improvements in net design and trawl configuration by considering the behavioral features of fish are made. Our original formula of E is modified for general use. Bycatch problems in the regional prawn fisheries and their possible impacts on fishery planning and development in Papua New Guinea as a developing country are discussed. The gear tested may offer enormous ecological and economic benefits. The gear is multipurpose, extremely simple, and can also be used as a biological sampler