The problems involved in the management of multispecies fisheries in Japan can be categorized into four major groups, namely (i) the incidental by-catch problems generated by the structure of fishing gear, (ii) the “successional fishing operations”1 directing fishing effort to a variety of fish species, (iii) the irregular and large changes in stock abundance and/or species composition of an exploitable fish community brought about by natural causes, and (iv) the efficient utilization of the ecosystem as a whole in a limited area/water.
Incidental catch problems are generated by fishing gear that catches more than one species by a haul or a shot, regardless of whether this is intentional or not. In a highly efficient gear such as bottom trawl or purse seine, the amount of by-catch taken is sometimes so large that it causes serious problems in the management of fisheries and resources.
Even when fishing operations are limited to a specific water, the species composition of the catch in each haul differs according to the time-spatial variation of the distribution pattern of the fish caught. This includes variation of species composition in the sea resulting from the infinite possibilities for the displacement of fish, variations in location and features of fishing grounds (oceanographic and/or bathymetric conditions), seasonal and/or diurnal differences in the fishing operations performed, etc.
The fishing strategy and tactics adopted by the fishermen also cause differences in the species composition of the catch. For instance, fishermen generally aim to catch prime species of high commercial value. As a result, fishing operations are usually characterized by frequent and quick changes of fishing ground from one water to another, which cause a substantial difference in the species composition of catches. The species composition of a catch is therefore the result of complicated and dynamic changes in both the (i) distribution pattern of fish taken and (ii) type of fishing method employed.
As a result, the amount and composition of incidental catch generally vary greatly even if the fishing gear employed is fairly strong selective action, with the exception of a few specific fisheries, e.g. skipjack pole-and-line, tuna longline, saury dipnet, herring drift gillnet or squid jigging fisheries, etc. It is technically very difficult to reduce the component of incidental catch in the entire catch as the ratio between the two is not a simple and independent parameter of fishing but the result of a combination of various factors and conditions, as described above.
There are two possible ways to deal with the by-catch problem. One is to manage the fishing to minimize the by-catch by adjusting gear and grounds as far as possible, and the other is to introduce suitable management measures specifically designed to reduce by-catch component of the fishery or fisheries in question. In Japan a combination of these two approaches has been employed, which has worked fairly well. However, it should be noted that the Japanese-type management scheme is unique in that the catch quota system has rarely been employed for management purposes, especially for catching finfish. This will be discussed in further detail in each of the later sections of this paper, with practical examples (see Section 2 for a discussion of the basic legal arrangements).
1 See Subsection 1.2 for a defination, and Section 3 for the details.
In waters where the catch quota system is employed, one way to resolve the problem is to establish a special catch-quota system taking into account an allowable by-catch ratio in the total catch of the entire fishery in question. This method was actually employed for international fishing for demersal fish stocks on the Georges Bank during the 1960's and 70's. It worked fairly well. The major regulatory measures established and implemented by the International Commission for Northwest Atlantic Fisheries (ICNAF) for this purpose comprised a set of catch quotas for all the major species caught in the conventional waters of ICNAF.1
By-catch also hampers the effective application of the regulations on mesh size for certain species. Since the theoretically derived optimum mesh size differs largely by species, it is technically impossible to apply a single mesh size regulation to a number of different species.
A structural feature inherent in small-scale fisheries also needs to be taken into account when examining multispecies problems. Local small-scale fisheries usually tend to employ simple and easy-to-operate gear aimed at catching high value fish species. Success in fishing operations is determined by various factors, e.g. fishing methods, accessibility of fishing grounds and the density of the target fish schools. Therefore, at the early stages of the development of these fisheries, the fishing gear employed was quite simple and the fishing grounds were confirmed mostly to nearshore waters. However, competition or conflicts between fishermen were not serious at that time since the fishing population was small.
As the fisheries developed, the fishing for a few specific fish species of high commercial value began and became more and more widespread. Competition among these fishermen thus arose in coastal waters, and was strengthened being coupled by a steady increase in the fishing population. Nearshore fisheries became less profitable for individual fishermen owing to a decrease first in the individual catch rate and second in the total catch, which boosted further competition among coastal fishermen. This general pattern can be seen during the development of many coastal fisheries before suitable management measures have been introduced. It should be noted, however, that a similar situation still exists in many coastal fisheries in the world today owing to a lack of adequate management actions.
In addition, the highly unstable nature of the fishing business needs to be taken into account when multispecies problems are examined. The catch rate and the total catch have always been subject to large fluctuations caused by various factors, e.g. fluctuations in abundance and density of target species, in oceanographic conditions, etc. It is traditionally said in Japan that the fishing business is a totally uncertain affair (“Ryo wa mizu-mono” in Japanese).
In order to minimize the uncertainty involved in fishing, it is better or safer for a fisherman to rely on multiple fish species rather than depending on only a single or a few target species. Such fishing operations can be performed with less risk and profitably by changing fishing gear in different seasons and grounds. Such operations also enable fishermen to increase the length of the fishing season or operation. The fishing strategy employed under such a multi-disciplinary philosophy can be called Successional Fishing (see Section 3 for details). It should be noted that almost all Japanese zcoastal fishermen employ this strategy.
However, it should be stressed here that full knowledge of the resources in question and adequate legal arrangements for proper management are indispensable for “successional fishing” mentioned above. The knowledge refers not only to the movements and behaviour of fish, which are closely linked to catchability, but also to the important biological features of the fish for management purposes.
It has usually been observed in recent years that a new fishery, once begun, grows very rapidly. The number of vessels employed increases as does total catch taken, which often results in an unfavourable impact upon the abundance and reproduction of the target stock(/s). If the stock abundance declines seriously as a result, the fishery may soon be compelled to shift target species, probably to a less valuable species than the one aimed at before. In the coastal waters around Japan such a process took place during the 1950's and the 60's, an example of which will be given in Section 6 of this paper.
Apart from the overfishing mentioned above, a shift in target species is sometimes required by the change in abundance caused by natural factors beyond human control. The large fluctuations frequently observed in the abundance of coastal pelagic fish stocks around Japan are typical examples. To cope with such natural fluctuations, the fisheries have to change target species in accordance with the substantial change first in the abundance of a specific fish species and second in the species composition of the exploitable community in the waters concerned. A fisheries forecasting service would be an effective way to reduce the uncertainty involved in fishing for these stocks. In Japan, the fisheries forecasting service has been actively employed for coastal pelagic fish stocks since the mid 1960's, and has contributed a great deal to the fisheries concerned (Yamanaka et al., 1988). Needless to say, however, such a service can only be exist when the resources research and adequate fisheries management are assured.
It has been generally observed that if the flexible strategy mentioned above is employed, the species combined total catch from the target fish community shows a fairly stable trend even when the abundance and the catch of individual fish stocks fluctuate greatly. This will be discussed in further detail in Section 5 of this paper.
When fisheries operate both extensively and intensively, harvesting various fauna and flora in the waters in question, the fishing strategy must be based on a different approach, namely the harmonious and systematic utilization of the ecosystem in the waters as a whole. In such cases, isolated management schemes aimed at a specific (or a few) living resource(/s) may not effectively protect that resource(/s) and the entire community in the waters. To achieve this end, full account must be taken of the followings; (i) the structure of the ecosystem in the waters in question, (ii) the inter species or inter species-group relationships among all components of the fish community and (iii) the socio-economic conditions of the fishing community.
Generally speaking, each fishery 1 selectively utilizes only a segment of various living resources which compose an entire ecosystem in the waters. In the sea, the fish of commercial value are mostly at higher trophic levels, which implies that the total biomass of those fish is strictly limited by the biomass of prey at lower trophic levels, resulting in a relatively small quantity of commercially valuable fish. The biomass of planktivorous fish is, in contrast, generally huge but the catches are of lower commercial value.
In waters where a variety of resources are available at various trophic levels of the ecosystem, a careful choice must be made regarding the priority species to be utilized. For instance, a decision must be taken on whether to catch (i) only highly valuable fish in relatively small quantities but with higher profit, (ii) less valuable fish in large quantities, or (iii) a combination of these. Furthermore, the strategy decided on should be flexible. This will be discussed in further detail later in this paper (see Sections 6 and 7).
Figure 1. The coastal waters around Japan divided into sea areas for statistical and management purposes. Each of the sea areas is further sub-divided into a few local sea areas for management and co-ordination purposes (66 in total).
The authors present in this paper a discussion on the four different types of approach employed in the management of multispecies resources and multi-gear fisheries in Japan, with clear practical examples given. An overall discussion is then presented from a managerial and industrial point of view.
Figure 1 shows the division of waters around Japan into different sea areas for statistical and management purposes. Frequent reference will be made to these sea areas throughout this study.
