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Clearly the characteristics of a fishery determine to a considerable extent the possibilities of controlling fishing effort by regulation. In this section we consider six main types of fishery: for small pelagic species, mid-water and demersal trawling for relatively few species, multi-species demersal trawling, for tunas, for sedentary species and for highly vulnerable and andromous species. In characterizing these types of fishery we are conscious that no one fishery will conform exactly to our classification. We hope nevertheless to be able to highlight important differences between the possibilities for managing fisheries of each type.

4.1  Pelagic fisheries

In terms of volume, fisheries for pelagic species are by far the most important in the world. The life span in pelagic species varies considerably; from one or two years in the case of some anchovies to up to twenty years in the case of the Atlanto-Scandian herring. For management purposes, it is best to distinguish between the short lived - anchovies, sardines, sprat, capelin - and the longer lived, such as herrings and mackerels. Many, if not most species have demonstrated dramatic declines in recruitment following or in association with reductions in the spawning stock (Ulltang, 1980). Often, even after fishing has been reduced or stopped, some stocks fail to recover (Daan, 1980). Many stocks also undergo long-term variations in abundance independently of any fishing effect (FAO/IOC, 1983).

Purse-seining and directed mid-water trawling for such species typically show no relationship between catch per unit of effort and stock size (Ulltang, 1975 and 1980). Direct monitoring of stock abundance is best done by acoustic methods. The techniques of virtual population analysis and cohort analysis are quite inadequate for assessing the status of short-lived pelagic species or long-lived species which have been heavily fished (Bailey, 1980; Ulltang, 1980). The reason is that the heavy fishing reduces the size of the older age groups and the stock dynamics are dominated by the younger age groups. The abundance of such age classes cannot be assessed with any real accuracy using VPA or cohort analysis. In short-lived species the level of natural mortality is such that this situation prevails even in the absence of fishing.

Clearly there are significant conservation problems in managing pelagic species. Some of the most dramatic declines in fish stocks have come from pelagic species (Glantz and Thompson, 1981; Zuleta and Serra, 1984). There is therefore a major requirement to ensure that there is some reasonable escapement of the spawning stock.

There are a number of economic and social problems which pelagic fisheries tend to generate. For long-lived pelagic species there is often competition between fisheries for meal and those for human consumption. Meal fisheries typically concentrate on the more abundant younger age classes. Fisheries for human consumption usually have some minimum marketable size. Direct competition between such groups in the absence of regulation will tend to favour the industrial fishery as it is able to exploit a year class before it recruits to the food-fish fishery. Unregulated fisheries of this sort have led to dramatic declines in highly productive stocks. The North Sea herring collapse (Saville and Bailey, 1980) is a well known example; others are documented in a variety of papers in Saville (1980).

Conflict between fisheries using highly mobile gear and fixed gear fisheries are particularly acute in fisheries for pelagic species. As indicated earlier, catch rates of mobile gear are largely independant of the stock size. Catch rates of fixed gear tend to reflect the abundance of the stock more faithfully. Accordingly stock declines will initially have little economic effect on mobile gear operations, while that operating fixed gear will face severe disruption.

Since pelagic species in general are highly mobile, a number of pelagic stocks will be shared between the EEZs of different coastal States. Hence, problems of management are exacerbated by the need for international agreements on regulation.

Over-capitalization in fleets exploiting pelagic species can be particularly pronounced. There are two reasons. The first is that the availability of pelagic species is a seasonal phenomenon and hence there is an incentive to expand capacity to try to ensure a large catch in a limited time. Secondly purse seiner design facilitates the construction of larger vessels with greater capacity. These factors tend to create a need for some regulation of the fleet size and capacity.

Management of short-lived pelagic species by TACs is likely only to be feasible if there is a programme of regular surveys of the stock. Such surveys need to be carried out just before the main fishing periods.

Virtual population analysis and cohort analysis may be used for stock assessment in long-lived species, but have value in setting TACs only if fishing intensity is relatively small. A high level of fishing mortality effectively produces a short-lived species which requires direct methods for assessing abundance.

If recruitment collapses are to be avoided, management goals should include some assurance that the spawning stock is not reduced below a reasonable level. This will require monitoring of both catch and stock abundance. It will be correspondingly expensive, especially if the aim is to obtain as high a yield as possible.

A judicious use of closed areas and seasons may be a good method for reducing fishing mortality on juveniles. Many pelagic species have a marked degree of geographical separation of the young age class at certain times of the year. A number of such measures have been attempted in managing such species in the North Atlantic. Unfortunately they have often been applied too late (Saetersdal, 1980).

Size limits and the use of mesh regulations are alternative methods of reducing mortality on the juveniles and improving the spawning stock. Mesh regulations are likely to be of relatively little use in pelagic fisheries; they are useless with purse seines and even in midwater trawling need to be accompanied by gear restrictions such as a limited time for towing. However, a minimum size limit enforced at landing can alter the fishing pattern in a beneficial way.

Direct control of fishing effort by licensing is unlikely to be successful in controlling the fishing mortality on the stock unless a very conservative policy to the number of licences issued is adopted. The reason is that catch rates in pelagic stocks do not tend to decline with the stock size. This means that in poor years the total catch will not decrease and the stock will tend to be further reduced. Pelagic stocks anyway tend to fluctuate for natural reasons in a marked manner. Hence there is a problem that a period of low stock size which has occurred naturally may be extended by the fishery, with accompanying risks of collapses in recruitment.

There are no particular special factors associated with the licensing of pelagic fleets to control over-capitalization. By contrast fisheries for pelagic species may present administrators with a whole set of problems involving conflict between different sets of fishermen. In general resolution of these conflicts in favour of low capitalized, less mobile groups will tend to have conservation benefits. There are two reasons. Firstly, less mobile gear tends to have a catch rate that is more closely related to stock size than mobile gear. This means that, in poor stock years, catches taken by the less mobile gear will tend to fall. Secondly, the target for the less mobile gear tends to be the older and larger age classes. Unless catch rates on these age groups are very high there is a relatively low risk of a reduction in spawning stock leading to a recruitment collapse.

4.2   Fisheries for demersal and semi-pelagic species in temperate waters

There are a whole set of species in temperate waters which lie on a spectrum from the truly demersal flat fishes to the mid-water semipelagic species such as hakes and whiting. Fisheries for these species are economically important as the species are of high unit value.

In such species there have been few dramatic failures due to a recruitment collapse. Possible exceptions to this are the Arctic cod (Garrod, 1977), the grey Pacific cod (Ketchen, 1961; Westrheim, 1978), and the Georges Bank haddock. Conservation problems are usually associated with what may be termed growth over-fishing or more simply with a fishing mortality well beyond that giving the maximum yield per recruit. Often the fishing operates on younger age classes which, in the absence of this fishing mortality, would increase significantly in biomass in later years. Although recruitment failure has not often been observed, this does not imply that drastic reductions in fishery yields have not occurred. The catch of yellowfin sole in the North-East Pacific was in excess of half a million tons in 1961; in 1981 the catch was 77,000 tons. Yet more drastic is the decline in catch of the Pacific Ocean perch. The 1975 catch was just under half a million tons, it dropped to 13,000 tons in 1979 and the 1981 catch is still only 26,000 tons. These figures are somewhat misleading as peak catches tend to occur as the unexploited biomass is fished down to and beyond the level producing the MSY.

There are few examples of species of this type remaining at low levels of abundance for extended periods in the absence of exploitation. Indeed, most such species appear to respond quickly to decreased exploitation. However, in some of the species and in particular in cods and haddocks the year class strength can vary massively. The ratio of the highest to lowest year class in such species can be of the order of one thousand (Hennemuth et al, 1980). Mortality rates are typically small, and the species are relatively long-lived (Pauly, 1979a).

These characteristics can present significant management problems, as the variation in stock size will tend to increase substantially with exploitation. This is because the more exploited the fishery the greater is the proportional contribution of the recruiting year class. Heavily exploited fisheries will tend to be dependent on a few year classes; where recruitment is highly variable, this can present problems, in varying income levels of the fishermen and disruptions to marketing patterns.

Except where the fishery is prosecuted on spawning concentrations, usually catch rates appear to be proportional to abundance. Although there are problems of calibrating increasingly efficient effort, they are relatively straightforward. Hence controls on fishing effort will provide fairly close control of fishing mortality.

Assessment of the stock size and status is relatively straightforward. VPA or cohort analysis can be performed as long as reliable catch at length or age data are available and in most cases such assessments should be reliable. There is a corollary to this observation. If management relies on catch data for making scientific assessments of the status of the stock, it will be necessary to institute a programme to ensure that the data are collected in a reliable manner. This can be expensive. There are two important management problems generally associated with fisheries of this type. Fishing tends to occur on smaller individuals unless regulated. The regulation of the size of the catches often results in high discard rates.

The second problem is that there are significant levels of by-catch, in the sense that the target species will rarely be the only species caught. There is a particular tendency for small-sized individuals of a non-target species to be caught and discarded.

Discards also tend to occur even in the absence of minimum size regulations as the market value of species of this sort is usually dependent on size. Large individuals can be considerably more valuable per unit weight than the small (Gates and Norton, 1974), accordingly, there is a tendency for there to be high discard rates of small individuals when hold capacity is under pressure, or when there are quota limits on individual vessels.

Regulation by catch limits: This is the most common method of control of such fisheries in the developed world. The main problem is that under-reporting of catches tends to occur. This presents major assessment problems if the data are unreliable and cohort or VPA analysis are the only methods of assessing the stock size. In the same manner, catch limits in isolation (which are usually enforced as landing limits), even when allocated to individual vessels, will tend to result in a high level of discards. This also can lead to unreliable scientific assessment as well as the obvious economic loss. Unreported by-catches or discarded by-catches pose similar problems.

Such fisheries therefore tend to be managed with a number of different regulations concerning the size of the catch and the level of the by-catch. Mesh regulation is common but can be difficult to enforce. In some cases it may be appropriate to prohibit the manufacture or import of nets below a certain mesh size. Mesh regulations tend to be unpopular with fishermen who claim often that they are irrelevant to their needs. The problem of demonstrating the benefit of such regulation in terms of increased yield to the fishermen has already been discussed. In the North Atlantic, for many years mesh regulation in isolation was the only method of controlling the fisheries. It is probably a useful accompaniment to any control of fisheries of this type but is insufficient by itself to provide adequate protection to the stocks. There is a claim that the more successful fishermen within a group tend to operate with larger mesh nets even in the absence of regulations. Presumably this is done to avoid the trouble and expense of having large numbers of discards.

Seasonal closures often present severe economic problems in that marketing is disrupted. They are not particularly successful in solving management problems unless there is a need for regulating a fishery on spawning shoals for conservation or ‘fish quality’ reasons.

Closed areas can be used with some success in such fisheries to protech either certain species or size classes. Typically smaller size classes tend to be nearer inshore and closure of these areas can control fishing effort on these groups. A significant problem is that such areas tend to be exploited by the less mobile fishery operators. More mobile gear typically operates further offshore on older individuals. In such fisheries there may therefore some justification for a preferential treatment of the more mobile gear in any allocation of catch limits or licences.

Over-capacity in fisheries of this sort has been severe (ICNAF, 1968); it has also been treated with subsidies with considerable problems (Brochmann, 1984a).

4.3  Tropical multi-species fisheries

In a number of tropical areas the species composition of the fish catch is highly diverse, typically several tens of species in a single trawl. The management of fisheries on such communities poses rather special problems. A recent symposium (Pauly and Murphy, 1982) is recommended as a comprehensive introduction to the management problems posed by such fisheries.

The first problem is that catch rates on the community can decline substantially with increased effort. In the Gulf of Thailand, where an increase in fishing effort has been accompanied by a research programme, catch rates in research surveys have declined by 80 percent between 1963 and 1975 (Boonyubol and Hongskul, 1978). In other areas less well documented declines in catch rates are believed to have occurred. Pope(1979b) considered the properties of the production model applied to the whole community, and Gulland (1982) reviewing this work indicated that such analysis could be used to determine whether the reduction in effort could lead to a greater yield from the community. However, the main conservation problem is what has been termed by Pauly (1982), ecosystem over-fishing. This dramatic name describes the somewhat less dramatic process where the species composition of the community moves from one dominated by larger teleostean fish, to one dominated by smaller fish and invertebrates. This has happened in the Gulf of Thailand, in several areas around Indonesia and off Malaysia (Boonyubol & Hongskul, 1978; Pauly, 1979a; majid, 1984; Sardjono, 1980). The problem is that this change in composition tends to reduce the value of the catch in that a significantly higher proportion of ‘trash fish’ are now caught. While in the surveys in the Gulf of Thailand the catch appears to reflect changes in the fish community, this may not be true of commercial catches. This adds to the difficulties of assessment.

Although the problem is easily state, its solution is not. There is at present no body of theory which will predict the effect of different catch levels on communities of this sort. Pope (1979) attempted to develop extensions of simple production modelling to such communities. It is not clear either whether such approaches are valid or whether they can be applied to data typically collected by fisheries of this fort. Pauly (1979a) reviews the management problems of such systems and proposes a number of interesting hypotheses, He does not develop these hypotheses to a level where they can be used to assess the impact of different catch levels on the community. A number of papers in Pauly and Murphy (1982) review the state of the theoretical art.

Despite this lack of coherehnt theory, it may reasonably be supposed that somewhat lower catch levels would have a less distorting effect on the community structure. This means that there will be a potential trade-off in the fisheries on theses communities, between the catch level and its species or size composition.

A related problem concerns the size composition of the catch and the selection of the gear. An attempt has been made to look at the potential benefits in increased yield that might be expected if mesh regulations were instituted (Jones, 1976). This problem has often been stated, but not solved, Optimum sizes of first capture differ between the different species and hence defining an optimum for the system depend on the relative values of each. Furthermore, such calculations can strictly only validly be made when the species do not interact in a biological way; clearly they do. Despite these problems, there could well be advanatages to be gained by altering the mesh size of the fishery. The choice of size would however be largely arbitrary. An additional difficulty is that shrimp are high value, of small size, and apparently benefit from the reduction of other species in these communities.

For all these reasons, regulation of catch levels and mesh size cannot be considered as primary management tools at this stage of knowledge.

The changes in community structure and in the reduction in catch rate have produced very difficult problems of social conflict. The shift towards trash fish is most detrimental to the artisanal fisheries who typically seek fish for food. By contrast the high value of shrimp and the increased proportion of shrimps and squid in catches by offshore trawlers has meant that their operations have suffered less economic hardship than would otherwise have been the case.

Control by licensing has been the measure whereby attempt has been made by the authorities to restrict the catch level and, it is hoped, the change in composition. The success of such measures cannot easily be assessed at the moment as data have accummulated relatively slowly and measures to restrict the licences have either been relatively unsuccessful or too recent to assess (Majid, 1984). The ban on trawling by Indonesia affords an important opportunity for monitoring its effect on community compoisition and catch rates.

4.4  Fisheries on sedentary species

Sedentary species such as clams, oysters, crabs and seaweeds, and marginally less sedentary species such as lobsters, reef fish and some crabs, proived rather special management problems. Conservation problems are significant due to the vulnerability of the species; however, recruitment - although variable - does not appear to be related to the adult stock. Recruitment catastrophies are correspondingly not a significant problem. The species are however vulnerable to growth over-fishing and without regulation there is a tendency to substantially reduce the larger specimens until the fishery is concentrating on the smaller and less valuable. Their sedentary nature renders the management of the species by the allocation of property rights an obvious choice. This ahs often been the manner of management; well-known examples are the Chesapeake Bay oysters (Christy, 1964), lobsters off the coast of Maine (Acheson, 1975) mussels beds in many part of northern Europe, coral reefs in the South Pacific (Johannes, 1978), and Breton seaweeds. Often such fisheries exist on a small scale, but have nevertheless been economically successful. They have rarely produced conservation problems. Exceptions are where physical damage can be done to the habitat, for example, by fishing for reef fish with dynamite or muro-ami.

Where there have been no property rights, or public pressure has eroded existing rights, management has usually been conducted on the basis of closed seasons and size limits. Such management is highly suitable for crustaceans and successful programmes have been implemented on a variety of crabs, abalone and lobsters (Johannes, 1978).

Often gear regulation can enable effective size limits to be introduced without the special monitoring required to police them. Usually such gear regulations are aimed at ensuring that smaller specimens escape.

Where there is significant sexual dimorphism, some care must be taken in the choice of size limit. In the fishery for Dungeness crab, few females are retained as they only rarely exceed the minimum size.

Although such regulations can and have been successful in solving conservation problems, there are nevertheless significant problems of economic inefficiency where the entry to the fishery is unlimited.

Licence limitation schemes have been tries for abalone in several parts of the world, but other licence limitation examples for such fisheries are rare.

Sedentary species are particularly vulnerable to mobile operations which can threaten the productivity of the resource for local populations. Where highly mobile operations develop for sedentary species some allocation in favour of local communities may become necessary.

4.5  Fisheries on highly vulnerable species

Certain species, because of their life history, are highly vulnerable to fisheries. Where significant over-capacity exist in the fishery, acute conservation problems are presented with extinction of particularly stocks being a real possibility. Andromous species such as salmon are often vulnerable in this way as are those species which concentrate in large shoals for spawning e.g., certain herring. Some marine mammals, which at breeding times are readily accessible: humpback whales, right whales and fur seals, are similarly vulnerable. In fish stocks the main conservation problem is thus to ensure adequate from the fishery.

The main method for managing such fisheries is by catch limits. Because of the vulnerability of the species, the catch limits are usually accompanied by a whole plethora of other regulations aimed at achieving some escapement. The fisheries on such species are usually concentrated in short seasons with mesh size, minimum size of fish and restricted gear and area regulations.

The allocation of the catch to competing units in the fishery tends to be done in a variety of ad hoc ways. Where a proportion of the TAC is allocated to a small group of vessels, some over-capitalization appears to occur. However, this is minor when compared to fisheries in which the fixed escapement policy is followed, but the catch is unallocated. In some of the fisheries for herring roe the entire TAC may be taken within a few minutes. Crutchfield and Pontecorvo (1969) noted that the extent of over-capitalization in one Alaska salmon fishery was such that the catch by drift gillnet vessels in Bristol Bay in the late 1950s could be taken by around one-sixth of the gear.

The allocation of property rights in such fisheries has tended to be eroded in the past by their very success. In the early history of salmon fishing in North America a number of property rights were adopted on salmon rivers. These generated such large economic rents that the result was an erosion of these rights by public pressure.

A somewhat different picture occurs for salmon fisheries in the United Kingdom. Property rights to salmon fisheries on rivers have tended to be eroded by the migratory nature of the species. Fisheries now exist on the high seas and in the estuaries as well as in the rivers.

In summary, the management of these highly vulnerable species is probably best achieved by aiming for constant escapement and managing for this where possible, by catch limits. Where catch limits are used, they need to be allocated preferably as a proportion of the available TAC. There is something to be said, in allocating these rights, for ensuring that individual profitability is not excessively high. Such methods could include monetary measures.

Where catch limits cannot be used, it will be necessary to operate some closed season or area to ensure the escapement of a reasonable size of the adult stock. Such methods are best operated with some form of restricted entry or control of effort.

4.6  Tuna fisheries

The tunas are conventionally considered as being highly migratory, but there is a whole range of behaviours from the relatively stable populations of tongol in the Strait of Malacca, through Pacific yellowfin which typically move around 5–600 miles to the trans-oceanic bluefin and albacore. However, most tunas occur in more than one country's EEZ and typically need to be managed by international agreements.

There is little evidence of declines in recruitment with stock size for most tunas, although there is some concern about bluefin. For some species there are conservation problems due to ‘growth over-fishing’, but the main management problems are those of over-capacity and the conflict between different user groups.

Monitoring the abundance of tunas is difficult. Acoustic methods are inappropriate, and although catch per unit effort, particularly of long-liners, appears to be related to stock size, the CPUE is highly variable making effort related analyses difficult. There are two main problems involved: the tuna appear to aggregate significantly on oceanographic features as well as on debris and around sea mammals (especially porpoise). This aggregation can lead to a weak relationship between CPUE and abundance (Clark and Mangel, 1979). The other problem is that different components of the fishery operate on different components of the population; long liners tend to catch the larger animals, surface fishing gear (e.g., pole and line) mostly juveniles. Purse-seiners can catch a range of sizes, depending on the mode of operation, such as by setting on porpoise schools or fish attraction devices. The problems of the inter-calibration of effort are correspondingly difficult.

The different size specific preferences of the fisheries present significant management problems, much in the way that meal and human consumption fisheries pose problems in the fisheries for pelagic species. Accordingly, managers will often be faced with significant allocation problems.

This is exacerbated by the fact that vessel catch rates are highly sensitive to the presence of other vessels. This decline in catch rates with increasing effort has resulted in some cases of gross over-capitalization.

Management of tuna by catch limits does seem to be possible, but the fine-tuning of the catch limits to approach the optimum level will require a high level of data collection. Without allocation of these catch limits the increase in fishing capacity is likely to be severe.

Where catch limits are not feasible, due perhaps to the cost of monitoring, the regulation by licensing or effort control can be attempted. As indicated earlier, such licence programmes are probably best achieved if applied in a conservative way. The potential for increasing effort efficiency on a fish species with such a highly developed behavioural pattern is significant. For much the same reasons it may be necessary to bring in gear restrictions or define licences on gear types.

Technical innovation can present mixed blessings in such fisheries if allowed to go unchecked. The recent development of fish attraction devices have been successful, but it has already been necessary to limit their use, e.g., by legislating that they must not be in eyesight of each other. Alternatives applicable in the Maldives, Samoa and the Philippines suggest a minimum distance apart for such devices.

The most well known by-catch problem in tuna fisheries has been the catch of porpoise associated with purse seine operation in the Eastern Tropical Pacific. This problem has been much reduced recently by changes in operational techniques. However, there are still by-catch problems. A particular complication in the mixed species catch of the long liners which can effectively stop the use of CPUE as an index of stock abundance. By-catch of other pelagic species are often associated with tuna catches. They can be of significant economic importance, e.g., in the Payao (fish attraction) operations in the Philippines (White & Yesaki, 1982). In addition there can be a significant problem of discarding of small fish including juvenile tuna by the purse seine high seas operation, especially when catch quotas or by-catch regulations are in force.

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