The Seto Inland Sea is a small, shallow and closed sea located in the southwestern part of Japan. It is connected to the outer seas by three channels: the Kii Channel in the east and the Bungo Channel in the southwest linking it to the Pacific Ocean, and the Kanmon Channel in the west linking it To the Japan Sea (see Figure 5). The inflow through the first two channels of the warm waters originating from the Kuroshio greatly affects the oceanographic conditions of the sea, but the influence of the two differs, dividing the sea into two subregions, the east and the west (Figure 5). However, the inflow of waters from the Japan Sea is locally limited to the westernmost part of the sea owing to the very narrow topography of the Kanmon Channel.
The entire area is about 18 700 km2 with a mean depth of 33 m and a total water volume of about 610 km3. The sea is characterized first by its temperate nature, being influenced by the Kuroshio, and second by its highly neritic nature, a result of its topography and large effluents from numerous rivers along the coast. These characteristics have created a unique and highly productive complex of living resources.
More than 3 000 species of aquatic animals and about 500 species of aquatic plants inhabit the sea. The number of species of commercial value exceeds 200. A distinctive characteristic of the living resources in the sea is that no species predominates by its biomass, except Japanese anchovy. This results in the formation of a unique, exploitable fish community as a complex of various species of small biomass. The annual catch of anchovy (including that of “shirasu”) usually accounts for about 35 to 40 percent of the total fish catch, which shows the highly neritic nature of the sea on one hand and suggests a plentiful supply of prey for carnivorous fish on the other.
The fish caught in the sea can be classified into three groups according to their life form. These are (i) those that migrate into the sea for spawning and move out to their major habitat in outer seas during the rest of the year,1 (ii) those that spawn in the outer seas and migrate into the sea seasonally or at sometime in their life stage and (iii) those whose entire life cycle occurs in the sea. The first group includes red sea bream and Japanese Spanish mackerel; the second, Japanese amberjack, Japanese sardine, Japanese chub mackerel and Japanese Jack mackerel;2and the third, various sedentary species, e.g. flounders, soles, rockfish, croakers, largehead hairtail, lizardfish, Japanese sea bass, grunters, grunards, pony fish, sandlance, etc.3
Prawns/shrimps, cephalopods, and most of the other animals are sedentary species. Prawns and shrimps are one of the most important species groups to the fisheries in the area as the total catch taken from the sea usually accounts for about 40–50 percent of the total shrimp catch from the entire Japanese coast. Major species include kuruma prawn, green tiger prawn, shiba shrimp, tora velvet shrimp, whiskered velvet shrimp, moebi shrimp and southern rough shrimp.4
The fisheries in the Seto Inland Sea are all of small scale, being composed of various multi-gear fisheries. Although the principles of the management employed in the region are the same as those for all the coastal waters around Japan (see Section 2), the limitations and the regulations imposed on the fisheries in the sea are the most specific and the most strict. This is a result first of the enormous value of the sea not only to the fisheries but also to the nation, second of the comparatively large production of fish 1 from a narrow and shallow sea area with high fishing populations along the coast, and third of special requirements for conservation related to topography and biological diversity of the sea where spawning, nursery and fishing grounds are all distributed in a narrow sea area.
4All are FAO defined names (Holthius, 1980).
Figure 5. The topography and subregions of the Seto Inland Sea referred to in this paper (Tatara, 1981, 1981a, modified by the authors).
The flexibility of the fishermen in changing their fishing from one species to another is another distinctive feature of the fisheries here although this type of fishing is by now practiced by almost all coastal fishermen in Japan. Strict regulation and flexible fishing appear superficially to be antipathetical but they actually supplement and support each other, a fact that will be discussed in detail in the later part of this subsection. The region-specific measures currently employed are summarized as follows.
All the large- to medium-size fisheries, subject to licence by the minister, are prohibited (trawl, purse seine, boat seine, etc.)
The number of medium-type boat seines, specifically defined as the Seto Inland Sea Boat Seine Fishery (5–15 gross tons), in each of the prefectures is nationally limited by the minister.
Mechanized trawl larger than 5 gross tons is prohibited, and the number of those smaller than 5 gross tons (specifically defined as the Seto Inland Sea Small Mechanized Trawl Fishery) in each prefecture is nationally limited by the minister.
The fishing methods of the trawl fishery mentioned above are permitted for one of the following: (i) trawl without any net-opening device, (ii) trawl with a beam, (iii) trawl with a frame (dredge-net), (iv) sailing trawl, and (v) others for which specifications and applicable sea area are defined separately.
Otter-trawl and two-boat trawl are prohibited. Beam trawl, dredge trawl and sailing trawl are permitted, but up to the total number mentioned above for each.
Acoustic fish finders and luring lights are prohibited, excluding particular fisheries in defined areas.
For various small-scale fisheries other than the above (vessels less than 5 gross tons) subject to the regulations defined by the prefectural governor, major regulations include:
limitation of total number of vessels by fishery,
permanent or seasonal closure of specific areas for conservation and coordination purposes,
mandatory seasonal lay-off of specific fisheries for conservation and coordination purposes,
mesh- and gear-size limitations,
body-size limitation (fish, clams, shrimps and lobsters),
prohibition of night fishing, excluding specific fisheries in defined areas.
A well-designed co-ordinating scheme and appropriate enforcement are required for the fisheries in the sea owing to their highly complicated structure and the variety of fishing gear/methods involved. This has been achieved in two ways, as discussed previously: on the one hand through central and local governments, and on the other by fishermen themselves through various functions/activities of fisheries cooperatives (see Section 2 for the legal arrangements and Section 3 for a practical example).
In addition to the actions taken directly by the minister or governors, the ministry has established a regional branch office, the Seto Inland Sea Fisheries Coordination Office, in Kobe, the capital of the Hyogo Prefecture located at the northeast coast of the sea (see Figure 5). The branch office is assigned the task of handling a part of (i) the co-ordination of the fisheries and (ii) the enforcement of conservation and management measures on site.
As the independent local authorities, fisheries co-ordinating committees have been established at two different levels in the region; there is a Sea Area Fisheries Coordination Committee in each of the prefectures bordering the sea (10 sea areas in total) and there is the Joint Seto Inland Sea Fisheries Coordination Committee. The committee members of the former represent the fishermen in each sea area (those elected by fishermen) and the public interest (those nominated by the governor). The members of the latter are composed of representatives from each of the sea-area committees (elected, usually the president of each sea area committee) and the experienced and knowledgeable men (nominated by the minister). The minister and the governor have to consult these committees when establishing new measures and modifying those currently employed, or dealing with disputes when they occur. All the fisheries co-operatives in the region are bound by the decisions made by these committees.
This is generally the same as that employed by all coastal fisheries co-operatives in Japan as discussed earlier part of this paper (see Section 2). In the Seto Inland Sea, however, characterized by its strong nearshore nature, the functions borne by cooperatives are the most important and effective, as seen in the example of the Hime-shima fisheries co-operative (see Subsection 3.1).
Co-ordination and regulation are mandatory and most strict in the fisheries included in the fishing-right fishery granted to fisheries co-operatives. This is because the details of management and co-ordination are legally entrusted to the co-operatives by the governor (see Section 2). However, fishing is usually co-ordinated not only within the framework of a fishing-right fishery or a licensed-fishery but for all fisheries, including aquaculture, in a entire coastal zone. This has been done either by single co-operatives in some cases or jointly by two or more co-operatives in others.
The total catch, all species combined, taken annually from the sea has ranged from 420 to 480 000 tons during the past decade, which accounts for about 5.5 to 5.9 percent of the total catch from the entire coastal waters of Japan, and is a substantial quantity from a narrow sea area. The catch per unit sea area is therefore high for the coastal waters around2Japan, especially for the southern regions, with about 21 to 26 tons/km2.
However, the production was not so high before the mid 1940's (before the Second World War), with an annual total catch of about 120–150 000 tons, but the catch was composed more of species of high commercial value than catches in recent years, and these were taken by various types of small-scale fishing gear. Although the catch rate (catch per unit effort) for individual fishermen was maintained at a fairly high level during the pre-war period, conflicts between fishermen over the best fishing grounds for profitable species were common among those using both similar and dissimilar types of gear.
Many complaints by fishermen about over capacity or overfishing during these periods were therefore a result of competition and the pursuit of higher profits, but not of concern about the decline in biological productivity (modern concept). It should also be noted that the legal arrangements for fishing industry were all feudalistic and fisheries coordination was left entirely to traditional and old-fashioned ways in those days.
Fishing in the sea, having slackened off during the Second World War, resumed and rapidly developed after about 1950 as the industry and the national economy recovered. In the meantime, re-organization of the legal scheme for fisheries had been undertaken, and a modern legal system covering all Japanese fisheries was finally established during the late 1940's and the early 1950's (see Section 2). The new scheme is highly democratic in its philosophy and structure, but the tradition and customs commonly kept to by fishermen were fully taken into account when the scheme was formulated.
In these circumstances and to meet the strong demand for animal protein caused by the serious shortage of food in the aftermath of the war, the total catch increased rapidly from 1950–55 and reached about 240–250 000 tons. The total catch, which had levelled off for a few years after the big surge, rapidly increased again during the late 1960's and early 1970's up to a level of about 400 000 tons.
The large increases in the total catch mentioned above were made possible by the overall recovery and development of the fisheries during those periods. However, the catch continued to increase even after the mid 1960's when the fisheries were considered to have reached maximum development in terms of the fishing grounds covered and fishing gears improved. Some changes favouring greater fisheries production may have occurred in the fish community in the sea, in addition to the increased fishing intensity.
Tatara (1981, 1981a) hypothesized, after examining biologically the two remarkable rises in the total catch mentioned above, that the enhancement of the sea's biological productivity took place in conjunction with the eutrophication of the waters during those periods. The enhancement meant first the greater capacity of the waters to support living resources (in terms of the nutrition available), second a larger biomass of fauna and flora, and ultimately higher catches for the fisheries. Figure 6 illustrates schematically Tatara's hypothesis (1981).
Figure 6. The annual total marine catch taken from the Seto Inland Sea from 1929 to 1976, together with indications on changes in the fisheries and their environment (Tatara, 1981, modified by the authors).
The hypothesis appears to be quite plausible as there is no doubt that nutritious effluents have substantially increased during these periods in accordance with rapid industrialization and the urbanization of the Seto Inland Sea coast. The nutritious enhancement, thus brought about, would have certainly facilitated greater primary production in the sea, resulting in larger populations of animals at higher trophic levels. The detritus and suspensions also might have been increased by a greater quantity of decomposers, which would have led to larger production of animals of lower trophic levels feeding on those items. It is likely that fishery resources in the sea would have been able to attain a larger biomass through this expansion of the ecosystem.
Thus, the total catch from the sea increased further beyond the maximum level of the development of fisheries at that time, although the implications of this assumption should be subject to further studies in the future. It implies, at the same time, that the structure of the ecosystem in the sea (species composition and inter-species functions) changed substantially during those periods, but this will be discussed in a later part of this section.
It should be noted, however, that various and serious side effects occurred during the initial stages of the rapid eutrophication. They were the pollution of sea water and the contamination of sea food. These problems occurred not only in the Seto Inland Sea but in almost all coastal waters around Japan. The public research institutes, fisheries, industrial and health administrations, worked hard for several years to establish new regulatory measures to control the environmental menace. The situation has much improved since a new regulatory scheme was established during the late 1960's.1
Pollution caused by agricultural chemicals, not thought to be closely linked with the eutrophication of the sea, was also common from the late 1950's to the mid 60's, even though the Agricultural Chemicals Control Law had been in force since 1948. This was concerned with the wide use of various chemicals (insecticides, fungicides, weed killers, fertilizers, etc.) to increase farm crop productivity and quality as part of the process of rapid modernization of all agriculture during the period, e.g. cereals, root crops, vegetables, pulses, fruits, nuts, tea and tobacco. Although no information or data are available, the damage caused to marine life by this type of pollution is likely to be most serious during the early life stages of fish, as they are extremely fragile and generally inhabit the shallower areas of nearshore waters. The situation regarding visible damage and, it is assumed, invisible damage too, has improved greatly since new regulations were established in the early 1970's, especially on insecticides of the residual type (i.e. the Enforcement Act for Agricultural Chemicals Control Law, enacted in 1971).
In the Seto Inland Sea, special arrangements have been made, in addition to the basic general regulations, in view of the great value and the topographical uniqueness of the sea.2 Thus, various strict regulations have been imposed since 1973 on all industries and local governments in the prefectures bordering the sea. It is not the main purpose of this paper to cover this subject in detail. However, a warning needs to be given here, because cases resembling that mentioned above are now becoming more and more common in the shallower parts of the coastal waters of many developing countries, especially in the tropics.
Apart from the direct man-made hazards mentioned above, a complicated side-effect has also accompanied the eutrophication of the sea. This is the occasional occurrence of the “red tide” caused by a burst and concentration of various phytoplanktons and zooplanktons in a limited sea area. The red tide, once occurs in coastal waters, sometimes seriously damages both the natural resources and aquaculture. Although the phenomenon can be observed in many coastal waters around Japan, especially in bays and inlets, it occurs most often and causes most damage in the Seto Inland Sea owing to the special topographic and oceanographic features, and presumably to its eutrophy. For instance, both the number of red tides and the amount of damage to the sea rapidly increased during the later 1960's, which coincided with the assumed completion of the first rapid eutrophication (see Figure 6). Thus, the fisheries research institutes and administrations initiated intensive research and took actions to establish appropriate counter-measures here too.
The great difficulty in handling red tide problems is the complexity and variability of their origins and effects. This is because many species of both phytoplankton and zooplankton are involved, environmental conditions promoting a sudden increase of particular types of plankton differ greatly, and their physiological influence upon animal life also differ from one case to another.1 This is a completely different situation from that regarding pollution or contamination that can be effectively controlled if surveillance and enforcement of the regulations are adequate. The subject falls outside the scope of this paper and must be examined in detail in another paper. However, it should be noted here again, as a warning, that similar phenomena becoming common in many coastal waters in the developing countries, especially in the tropics. A review of various cases observed in Japanese waters, the current status of research, knowledge so far obtained, counter-measures being taken, the prediction and forecasting service, etc. are well documented by Hanaoka et al., (1980).
The entire ecosystem of marine living organisms inhabiting the Seto Inland Sea can be divided into two subsystems according to their food-web. The energy flow of each is schematically illustrated as follows:
I. Piscivorous system
phytoplankton - zooplankton - fish - piscivorous fish
II. Omnivorous system
phytoplankton/detritus - zooplankton/benthos - invertebrates/fish -omnivorous animals/fish.
In addition to the above, various decomposers (bacteria, viruses, etc.), which decompose various resolvable organic items (e.g. carcasses of fauna and flora) into nutrition play a highly important role in the energy flow, especially in the sea. This must have been critical when a substantial change in the biological productivity of the sea was taking place. However, both the qualitative and quantitative features of these decomposers have been excluded from this study. Future studies dealing with the topic are awaited.
Some species bypass an intermediate stage of the flow, e.g. gizzard shad is a herbivorous fish so the energy flow is from “phytoplankton” to “fish” missing out “zooplankton” in this case. The fish is harvested by the shad fishery. In general, the fisheries harvest the animals or fish, as a commercial product, at various stages/levels of the energy flow in each system. For instance, the catch of anchovy and “shirasu” are products of the third level as planktivorous fish and amberjack (yellowtail) is at the fourth stage as a as piscivorous fish in the first subsystem. Similarly, abalone and sea urchins are at the second level, shrimps and soles are at the third, and sea breams and octopuses are at the fourth level in the second subsystem. However, these subsystems are distinguished by the fact that the highest level is represented by piscivorous fish in the first and omnivorous animals and fish in the second.
Generally speaking, it is not easy to examine these two subsystems through data observed in the field. Tatara(1981) applied detailed statistics 1to these sub-ecosystems to examine changes in ecosystem of fishery resources in the Seto Inland Sea. He allocated the catch by species and species-group into the assumed food-web group in each of the sub-ecosystems. Table 6 shows the results of the allocation employed (Tatara, 1981, modified by the authors).
Before going into the details of the results obtained, it should be noted here that the application of fishery statistics to such ecological concepts inevitably involves substantial bias and distortion caused by various factors. These factors include (a) the selective function of some types of gear employed, (b) species preference practiced by fishermen, (c) the change in food items (feeding habit) of fish according to growth stage 2 (d) the intermingling of fish to and from the region, etc. The simplification and/or approximation of “food habit” of a specific fish or species-group in allocating the catch data into the appropriate food web category (Table 6) also generates substantial bias.3
However, it is worth examining the ecological concepts of the catch and exploitable resources, as far as possible, to clarify the biological features involved in a systematic way. Such an examination could be carried out by analysing the data on a comparative basis, applying the same standards and rules within a defined framework.
The compilation of species caught, allocated into each trophic level by food item in each subsystem (from 1 to 4 for each, see Table 6), can be roughly regarded as representing the standing-state of the exploitable resources in the sea.1 However, it should be kept in mind that the total marine catch represents only a part of the biomass pyramid of the entire ecosystem. The mean value of the numbers of trophic level (as defined above) for the total catch, calculated by weighing the catch for each level, is an indicator of the “standing state” of the exploitable resources as a whole in terms of the centre of gravity of the biomass pyramid of the entire catch or exploitable stocks.2
Table 6. Allocation of species and species-groups to sub-ecosystem and trophic level by major food items. Figures are given in percentages (each species/species-group = 100%) (Tatara,1981, modified by the authors).
Food Item:
(PST): Photosynthesis PHP: Phyto-plankton ZOP: Zoo-plankton FIS: Fish ANM: Various animals DET: Detritus
(%)
| Food-web system 2 | ||||||||
|---|---|---|---|---|---|---|---|---|
| Planktivorous-Piscivorous system | Benthos feeding-Omnivorous system | |||||||
| Species/ species-group 1 | Trophic level and food item | Trophic level and food item | ||||||
| 1 | 2 | 3 | 4 | 1 | 2 | 3 | 4 | |
| (PST) | PHP | ZOP | f FIS | (PST) | PHP | ZOP | ANM | |
| DET | ANM | FIS | ||||||
| “Wakame” seaweed | 50 | 50 | ||||||
| Other seaweeds | 50 | 50 | ||||||
| Gizzard shad | 100 | |||||||
| Sardine | 50 | 50 | ||||||
| Anchovy | 100 | |||||||
| “Shirasu” | 100 | |||||||
| Chub mackerel | 100 | |||||||
| Jack mackerel | 100 | |||||||
| Butter fish | 100 | |||||||
| Sandlance | 100 | |||||||
| Amberjack | 100 | |||||||
| Spanish mackerel | 100 | |||||||
| Bastard halibut | 100 | |||||||
| Lizardfish | 100 | |||||||
| Sea bass | 100 | |||||||
| Other fish | 15 | 35 | 15 | 35 | ||||
| Largehead hairtail | 50 | 50 | ||||||
| Sea urchins | 100 | |||||||
| Sea cucumbers | 100 | |||||||
| Abalone | 100 | |||||||
| Top shell | 100 | |||||||
| Hard clam | 100 | |||||||
| Baby clam | 100 | |||||||
| “Mogai” clam | 100 | |||||||
| Pen shell | 100 | |||||||
| Other shellfish | 100 | |||||||
| Polychaeta | 100 | |||||||
| Other benthos | 50 | 50 | ||||||
| Other shrimps | 100 | |||||||
| Other crabs | 100 | |||||||
| Kuruma prawn | 100 | |||||||
| Mantis shrimp | 100 | |||||||
| Blue swimming crab | 100 | |||||||
| F. spotted flounder | 100 | |||||||
| Other flatfish | 50 | 50 | ||||||
| Mullets | 50 | 50 | ||||||
| Croakers | 100 | |||||||
| D.g. pike-conger | 100 | |||||||
| Red sea bream | 100 | |||||||
| Black sea bream | 100 | |||||||
| Common conger | 100 | |||||||
| Rockfish | 100 | |||||||
| Sharks | 100 | |||||||
| Skates | 100 | |||||||
| Cuttlefish | 100 | |||||||
| Squids | 100 | |||||||
| Octopuses | 100 | |||||||
2 See text for the details of the sub-ecosystems.
The annual change in the total catch from 1951 to 1977 by subsystem and subregion of the sea (east and west) is shown in Figure 7. All catches show a steady increase over the years, which accords with the change in the total production of the sea (see Subsection 6.3.1 and Figure 6). This indicates that the increase in the biological productivity of the sea applied to all resources and areas.
However, it is important and interesting to look at some differences in trend among the elements examined. First, the dominance of the two subsystems is reversed between the two subregions, that is, the piscivorous system is dominant in the east while the omnivorous system dominates in the west.
Second, the rate of increase in catch differs greatly by subregion and subsystem. It was the highest in the piscivorous catch in the east, which more than doubled during the period, while that in the west was rather stagnant although the total increase had nearly doubled. By contrast, the omnivorous catch in the east was rather stagnant over the years, while that in the west increased steadily, the catch more than doubling. These facts indicate that large and various differences in the processes increasing biological production in the ecosystem occurred depending on the structure of the system and, it is assumed, on the environmental conditions in each subregion.
Figure 8 shows the relationship between the annual index of standing state3 and the annual total catch by sub-ecosystem and subregion. All the relationships show a negative correlation. The curve moves generally from upper left to lower right as total catch increases. This means that the centre of gravity of the catch moved to lower trophic level during the period under review. It is interesting to note a consistent flatbottom tendency over the subsystems and subregions.
Figure 7. Annual change in the total catch by sub-ecosystem and sub-region of the Seto Inland Sea (Tatara, 1981a, modified by the authores). See text for the details of the definition and remarks of the sub-ecosystems.
Figure 8. Relationship between the annual total catch and the index of the "standing state" of the biomass pyramid of the catch by sub-ecosystem and sub-region of the Seto Inland Sea (Tatara, 1981a, modified by the authors). The index shows the "centre of gravity" of the biomass pyramid of the catch, which shows also a relative position of trophic level, see text and Table 6 for the details.
In the omnivorous system, the decline in the level was most marked in the western sea, while that in the east was the weakest overall and subject to large fluctuations. It can be seen in the piscivorous system that the curve has flattened out at a considerably higher level in the west than in the east. These facts suggest that more resources in the omnivorous system had become available in the west, while more of those in the piscivorous system became available in the east over the period. It is also noticeable that the resources at higher trophic levels were to be found more in the west than the east.
In conclusion, a change in the sea's ecosystem certainly did take place, in conjunction with the eutrophication of sea waters, from 1951 to 1977. But the changes in the structure of the ecosystem (biomass of each species and species-group, and supposedly, inter-species relationships, etc.) are markedly different between the east and west of the sea. These changes have resulted in differences in fisheries production between the two subregions as the final outcome of the enhancement in biological productivity. In other words, the fisheries in the Seto Inland Sea are dependent upon two different ecosystems, i.e. the piscivorous system in the east and the omnivorous system in the west.
Major changes can also be observed in a few specific fish stocks in the sea. Figures 9 and 10 show long-term changes in the annual total catch of a few selected carnivorous species taken from the entire sea over the past 34 years, 1951–85. All the fish are at higher trophic levels, feeding intensively on fish and other animals at their adult stage, and are of high commercial value. They include red sea bream, bastard halibut, daggertooth pike-conger, Japanese sea bass, Japanese Spanish mackerel, lizardfish (Figure 9), and largehead hairtail (see Figure 10). The stock levels of all these show fluctuations over the years produced either by man-made or natural causes. These are summarized as follows:
The first three species, red sea bream, bastard halibut and daggertooth pike-conger, are traditionally very important to the fisheries in the sea because of their high commercial value. The abundance of these species once declined substantially with the overall development of the fisheries in the sea, which resulted in a sharp and continuous decline in the total catch of these fish during the 1950's and 60's (Figure 9). The size of the fish caught also decreased during the same period. The loss in net economic return to fishermen harvesting these fish was serious caused by a decline in the catch rate coupled with a lower market price for fish of smaller size. These were apparently typical symptoms of overfishing, as far as these three species were concerned. It can be seen, however, that this overfishing occurred while the substantial increase in the total biomass of exploitable fish was taking place in the sea (see Subsection 6.3.2 and Figures 6 and 7).
These symptoms were soon recognized as serious by all the fisheries research institutes and administrations in the region, not long after the strong complaints were made by fishermen. However, there was no simple way to resolve the problem, because of the complexity of the fisheries and of the resources fished.
Figure 9. Long-term changes in annual catch of major carnivorous fish species of high commercial value caught in the Seto Inland Sea, 1951-85 (see Appendix Table 1 for statistics).
Figure 10. Long-term changes in annual catch of major carnivorous fish species of high commercial value by fish group caught in the Seto Inland Sea, 1951-85 (see Appendix Table 1 for statistics). In these circumstances, the local governments decided to modify the system of regulatory measures, and introduced strict and more comprehensive measures than those employed before. The adjustment had two principle aims. The first was the protection of spawning stocks throughout their life and in particular spawning grounds and seasons, and the second was stronger protection of the nursery grounds of these fish, which were commonly distributed in the seaweed-bed area (or “underwater sea grass forest”). Various additional limitations on fishing operations by efficient gear (e.g. mechanized surrounding seines for red sea bream or mechanized small-scale trawls for bastard halibut), closure of specific grounds to almost all fisheries during the spawning and breeding seasons, etc. have been imposed since then.
In the meantime, the annual total catch of the first two species began to increase (Figure 9). It started first in the catch of bastard halibut around 1965, about ten years after the initial decline, and second in red sea bream around 1970, about fifteen years after initial decline. These increases continued over the following years. Recent catches of bastard halibut far exceed those taken during the early development of the fisheries, and catches of red sea bream have almost recovered to their previous levels. The catch of daggertooth pike-conger still remains at a low level, but firm signs of recovery have been seen since around 1980, about 25 years after the initial decline (Figure 9). There is no doubt that these stocks have been consistently recovering in recent years.1
The recovery of these fish stocks would have been a result of various factors. The authors are inclined to hypothesize that the comprehensive and strict management measures employed in the fisheries in the sea, specifically those dating from the mid 1960's, played the most important role in the recovery. The increase in the prey biomass, mentioned previously, would certainly have aided the recovery too. However, the main trigger for the recovery must have been the employment of proper management, and not environmental factors. This must be examined in more detail by future studies. However, our hypothesis enables us to make a projection. Namely, a serious decline in stocks of these fish would not occur in the future only by man-made causes, if the enforcement of present management scheme is effectively maintained.
The other four fish species are Japanese Spanish mackerel, Japanese sea bass, lizardfish and largehead hairtail. Annual catches of the first three species had been fairly stable until around 1970 (Figure 9) and for the last, until around 1965(Figure 10). These were maintained despite the rapid development of the fisheries in the sea, which resulted in an overall increase in the total catch throughout the years. However, the catches of all four species have markedly increased, the first three since about 1970 (Figure 9), and the last since about 1965 (Figure 10). These phenomena indicate that a large increase in stock abundance had undoubtedly taken place for each of these species, too.
The species-specific biological features of these fish might have functioned to keep stock levels stable during the initial period. These may include the limited catchability of the fish by specific kinds of gear, e.g. gillnets, hook-and-lines, trolls and setnets are all passive in nature (see Subsection 5.2), and the movement of stocks to and from outer seas, etc. These would have prevented the fish being exposed to rapidly increasing fishing intensity by more efficient types of gear like mechanized purse seine, boat seine and trawl in the early stage of fisheries development in the sea. But this explanation should be examined in detail by future studies.
More important, it should be noted that a sudden and rapid increase in these stocks began during the period of 1965-75, consistently to all the species mentioned above (see Figures 9 and 10). Catches in recent years are double to triple what they were during the stable period for the first three species (reaching about 4–5 000 tons for each), and about 15 times what they were for largehead hairtail (reaching about 15 000 tons). These catches are assumed, with little doubt, to represent the current levels of these stocks. It is probable that the growing abundance of prey animals would have supported the increased biomass of these species. However, abundant prey cannot be the only factor responsible for the increase; another factor, or various others, must have been involved.
It should be noted that a similar phenomenon has been observed in the catch of filefish, Navodon modestus (Gunther). An extra ordinary increase in the catch has been reported from southern and western Japan since around 1965 (Kobata, 1981, Kanagawa Prefecture, 1981). Evidence of the growing numbers of the fish has been clearest along the central Pacific coast of Japan, where huge catches by setnets along the coast are frequent (Kobata, 1981). Unfortunately, the state of filefish in the Seto Inland Sea is not yet known as separate catch statistics are not available at present. However, the situation probably resembles that described above.1
It is interesting and amazing too, to look at the similar phenomena reported widely from the southwestern part of the Northwest Pacific Ocean. Remarkable increases in the catches of largehead hairtail and filefish have been reported from the waters along the west coast of the Korean Peninsula and northern China bordering the East China Sea (Chikuni, 1985). The timing of these increases concurs with that in the Japanese waters, during the period 1965–75.
At present, the main causes of these phenomena, in both the East China Sea and Japanese waters, are not clear, and future studies to be carried out by the institutes concerned are awaited. However, an important point to bear in mind (especially in connection with the subject of this paper) is that both largehead hairtail and filefish are eurybath in nature and omnivorous with greedy feeding habits 2, factors that must be critical in the inter-species relationships in the entire ecosystem of a fish community. This implies that observations over a wide area beyond the framework of the Seto Inland Sea are required, first to clarify the technical aspects involved, and second to establish adequate management measures, if needed, which may require a global scheme covering areas well beyond the Seto Inland Sea in some cases.
2These features may be clues that point toward an explanation of these changes.
In any case, an astonishingly large change in stock level of carnivorous fish species of commercial value has occurred in addition to large changes in the abundance of resources and the entire ecosystem in the Seto Inland Sea. The combined total catch of species whose stocks have recovered in recent years is more than 1.5 times the catch during the early development of the fisheries, and that of fish whose stocks have just recently begun to increase is nearly 3 times as high as it was in that period (Figure 10). Studies and appraisal are eagerly awaited to clarify these phenomena, as this is the first time that this phenomenon has been experienced in the history of the fisheries and resources in the sea. Apart from the natural causes involved, the authors believe that the success in fisheries management in the region has played an important role in these changes.
Apart from the capture fisheries discussed so far, the aquaculture fisheries have a highly important role to play in the comprehensive use of the sea. All the aquaculture fisheries are legally partof the “Demarcated fishing-right fishery”, which is one of the “exclusive-use right” fisheries of the coastal zone, together with the setnet fishery (see Section 2 and Tables 1 and 2). The majority of the rights have been granted to fisheries co-operatives especially those for culturing seaweeds and oyster, while those for fish and prawns are granted chiefly to individual fishermen or entrepreneurs. The aquaculture granted to a fisheries cooperative forms a very important element in coordinating all fisheries under the self-regulatory scheme of the co-operatives, particularly in coordinating the “successional fisheries”, as discussed in Section 3.
Aquaculture in the sea has a long history, especially that for oyster and laver(“Asakusa-nori”, red seaweed). Similarly to capture fisheries, aquaculture in the sea has developed remarkably after the Second World War. The development of the fisheries had nearly reached its maximum level around the mid 1960's in terms of the amount of space utilized, and annual total production reached about 150-200 000 tons. The production of these fisheries, however, continued to grow, benefiting from the improvement in aquaculture technology, and has reached a level of more than 300 000 tons level in recent years.
Besides the development of the traditional oyster and laver culture, fish and shrimp culture were initiated on an industrial basis in the sea in the early 1950's. Fish culture, (including shrimp culture1 other than specified), has developed rapidly in recent years, being boosted first by the remarkable development in rearing and artificial seeding technologies, and second by the plentiful and stable supply of fresh feed material since around 1970 (provided by massive catch of chub mackerel, sandlance and more recently sardine from the coastal waters around Japan). It has also been stimulated by the strong demand for its products, brought about by a change in consumer preferences toward luxurious sea food in recent years. The total annual production of fish culture has reached about 15–20 000 tons recently, which includes various species such as amberjack, red sea bream, Jack mackerel, bastard halibut, black sea bream, puffer, filefish, kuruma prawn and octopus.
The aquaculture in the sea can be grouped into two different categories: one without and the other with feeding. Seaweed (laver and “wakame” or Undaria pinnatifida) and oyster culture are included in the first group, while fish culture is in the second. Figure 11 shows annual production by type of aquaculture and by major species together with the total amount of feed used for fish culture during the past 15 years.
1Almost exclusively the culture for kuruma prawn.
Figure 11. Annual change in aquaculture production by type of culture and major species in the Seto Inland Sea, 1969-85. The amount of feed used for fish/prawn culture is also shown (see Appenndix Table 2 for statistics).
The nutrition required for seaweed and oyster is entirely natural. These is therefore no doubt that favourable environmental conditions over the years have greatly facilitated larger production of these aquaculture as well as other fisheries. In particular, the increased production of living resources in the sea in conjunction with the eutrophication of sea waters has played an important role in this group too. The current level of production (about 100–150 000 tons of seaweeds, 170–180 000 tons of oyster, totaling 300–350 000 tons) is as great as the capture fisheries' production at lower trophic levels (total production being 420–480 000 tons). The data are insufficient at present to look in further detail at the relationship between the eutrophication and the products. This needs future studies.
In contrast, fish culture production is very small in terms of quantity at about 15–20 000 tons in recent years, although it is great in value. Apart from its profitability, a notable fact relevant to the subject of this paper is that the feed used for fish culture is about 5–6 times the level of annual production, at 90–100 000 tons, of which about 95 percent is fresh or frozen fish, clams, shrimps, and/or krill. These must have accelerated the eutrophication of the sea, and occasionally caused pollution or the red tide mentioned previously. This implies that monitoring under comprehensive and careful management is required, covering all the fisheries in the sea.
The annual total catch from the entire sea has markedly increased during the period under review: 120–150 000 tons in the 1930's and 40's, 200–250 000 tons (1950's), 250–380 000 tons (1960's), 380–420 000 tons(1970's) and now approaching 500 000 tons in the mid–1980's. By the mid 1960's there was no room left for further development since the fisheries covered almost all the available fishing grounds in the sea and the annual catch was about 300 000 tons. In fact, the total number of fishing vessels in the area has not substantially increased since then. It is therefore clear that the remarkable increase in the total catch thereafter is attributable mostly to the increase in exploitable biomass caused by the greater productivity of the sea rather than the development of fisheries or the improvement in fishing technologies.1
However, this increasing productivity affected the exploitable fishery resources in different ways according which sub-ecosystem they belonged to. For instance, it favoured the production of a larger bio-mass of planktivorous pelagic fish in the east, and of the benthos/detritus-feeding animals in the west. As a result, the “centre of gravity” of the entire biomass of resources, and eventually the catch, has moved to a lower trophic level than before. In other words, the fisheries in the sea have been flexible and changed their target species (not a single species but a combination of species) in accordance with change in the exploitable resources.
This tendency can be observed not only in the fisheries as a whole, but also in the species-specific fisheries, which have also become more flexible according to changes in their target stocks. This type of flexibility is very important, particularly when the stock has been depleted by overfishing and strict regulatory measures are required for those stocks. If the fisheries can survive by flexible fishing in some way and the regulatory measures are enforced effectively, depleted stocks have a chance to recover. The fisheries can then resume fishing their original and profitable target stocks, once those stocks have recovered. The red sea bream and bastard halibut fisheries in the sea are two good examples of such a cycle (see Subsection 6.3.3, item (1)).
Such flexibility, not arbitrary but strictly managed functions for the fishermen concerned as compensation in some cases, and as further development or expansion of their fishing in others. The recent catch of carnivorous fish species of high commercial value may be an example of this (see Subsection 6.3.3 item (2)).
In conclusion, a fishing strategy based on a combination of (i) the flexible but well designed fishing by fishermen and (ii) the comprehensive and detailed management and coordination by fisheries administrations and by fishermen themselves is indispensable to achieve the best possible utilization of resources in a limited sea area. Management should cover both the capture fisheries and all the aquaculture of the region. Such a strategy would surely enable the fisheries and fishermen to survive in some way, even when substantial changes temporarily occur in target fish stocks for some natural or artificial reason (e.g. overfishing or pollution). This strategy would also ensure the harmonious and effective utilization of the limited sea area and resources, producing the largest possible benefit for all.
The “largest benefit” mentioned here does not refer only to maximum profits for a specific fishery or fisheries, but to the socio-economic benefits for all fishing communities in the region and the overall benefit to the national economy and welfare. The fishing strategy should therefore be decided first by the fishermen themselves according to the state of marine resources and the socio-economic conditions in each fishing community in the region, and then be controlled and coordinated by the fisheries administrations according to the priorities of local and national policy.
The authors believe that the fisheries management employed in the Seto Inland Sea, based on lessons learnt from past failures and success, is a good example of comprehensive utilization of fishery resources in a limited sea area.
