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Last updated Updated 14 April 2007
Fish and other animals from the sea provide an important source of protein for people living along coasts and on islands. Fishing in shallow coastal waters is an important occupation today as it has been for hundreds of years. The coral reefs, lagoons, seagrass beds, estuaries and mangroves are some of the most productive resources of tropical coasts.
Because the animals in the sea are living things that grow and reproduce, they are a renewable resource; that is, they can continue to be used over and over again if they are taken care of. When a fish is caught or a shellfish collected, another can grow up to take its place. However, if too many fish are caught at once, it may not be possible for the few that are left to replace all those that were taken. This is called overfishing, and today it is happening in many places in and around the oceans.
To avoid overfishing and other damage to fish resources, a fishery must be managed in accordance with certain ecological principles which are explained in the following sections. If local fishermen understand these principles, they can then decide on the kinds of management that will protect their fishery and keep it productive.
On the land, early peoples collected their food in the wild, digging up roots in the forest and collecting fruits wherever they found them. Later they learned that they could plant their food plants, and thus have more food than they could find in the wild. They thus went from hunting and gathering to agriculture. In the sea this change has hardly begun. In a few places people are learning to grow fish, shrimp, oysters and other sea animals, as well as seaweeds, as we do in farms on the land. This aquaculture is still at an early stage, and it requires a considerable investment and lot of scientific research to do it successfully.
Most fishing is still at the hunting stage. We collect for our use what is produced by the natural system, but we are not yet able to manage that natural system to produce even more of what we want. Because we have less control in fishing than in agriculture or livestock raising, we must learn to live within the limits of the natural productivity of the environment. At the most, we should try to avoid doing anything that might hurt that natural productivity and leave us with even less than would have otherwise been available. We therefore have to learn how much we can take from the natural system without hurting it. This is sometimes called the sustainable yield, and it may be only after a long period of trial and error that we can learn what it is. If we take too much, the system will produce less; if we take to little, some of the productivity has not been used; but finding the exact balance in the middle is not easy, particularly since natural productivity often varies. It is usually better to take a little less that we think is possible, rather than to risk upsetting the whole system.
Fish are just like any other animals in that they need food, shelter and good conditions for reproduction. A part of fisheries management is to ensure that these basic requirements are not changed for the fish you want to catch.
Each species of fish or other animal prefers certain kinds of food. Some fish may eat the plants and animals attached to the bottom, or little animals that swim in the water. Larger fish may well eat smaller fish. Some will feed in the daytime and others at night. It could be that food first made by seaweeds or other plants will be eaten by a snail, which in turn may be eaten by a meat-eating snail, which is then eaten by a starfish, which is eaten by a shrimp, which is eaten by a small fish, which is in turn swallowed by a larger fish, which is then caught by a fisherman if it is not first eaten by a shark. In such a food chain, each animal depends on the one below it. If something happens to one of the animals, the others above it may go hungry, or have to eat some less desirable food. On a coral reef where there are many kinds of animals, the food chains (or food webs as they are sometimes called because they have many branches) may be very long and complicated.
Since the fish and other animals are both looking for something to eat and afraid of being eaten, it is important for them to have some place to hide. They also need shelter if they are to survive storm waves and to avoid being swept away from the shore by currents. Environments like healthy coral reefs and mangroves provide good shelter for many kinds of animals, and this is one reason why they are so rich and productive. If mangroves are cut, or corals are smashed and broken, there will be less shelter and the fish populations will suffer accordingly.
No animal or plant lives forever. If a species is to survive and prosper, the generations must succeed each other. Each animal has its own time, place and conditions for reproduction when eggs are laid or the young are born. The tiny babies may not look like the parents, and may even go off and live in some other place before coming back as adults. Often the babies may be more sensitive and vulnerable than the adults, and some change that affects them will eventually affect the whole species. Since it is through reproduction that the fish caught by a fisherman are replaced, protecting and encouraging reproduction is very important to fisheries management.
Different species can have different strategies for reproduction. An animal may produce thousands or millions of eggs or young, but most of these will be swept out to sea, starve to death, be eaten up or find no place to grow up; only a very few will grow up to be adults. However, because there are so many, the chances of a few surviving are very good, and if something happens to one, another will almost certainly take its place. Other kinds of animals have found it better to produce only a few young, but to make them big and strong, or to protect them while they are small, so that their chances of growing up are much better.
The example of the giant clam will illustrate the problems of reproduction. Clams reproduce by squirting eggs and sperm into the water. If two clams are close enough to signal to each other through chemicals in the water, they may reproduce together and some eggs may be fertilized. The baby clams may swim around for a while before settling down to the bottom and growing up, assuming they are not eaten in the meantime and can find a good place to live. Where fishermen take too many clams, the few that remain may be too far apart to reproduce successfully, and when those are gone there will be none left. In some places in the Pacific Islands, local people protected an area with many clams, which could then reproduce and replace the clams taken all over the reef. It is even possible to move clams to be nearer each other and thus help them to reproduce. Otherwise overfishing of giant clams will drive them to extinction. It already has in some places.
The tropical ecosystems which produce most fish caught by local fishermen are very complicated, with many different kinds of species depending on each other and affecting each other. Because there are many different animals, there are many choices of food, many competitors, and many enemies, and thus many different ways the system can work.
Such ecosystems have generally existed for a very long time, so the animals and plants have had time to develop close relationships and many ways that they depend on each other. Big fish may depend on small cleaner fish to remove parasites on their skin and in their mouths that would make them sick. Clown fish depend on sea anemones to protect them from being eaten, and in turn they help the anemones to find food. Small shrimp and fish may share the same hole in the sand; the shrimp digs the hole, and the fish stands watch and signals if any danger is near. Giant clams are fed by tiny plants growing underneath their skin. Because of these relationships, a change on the reef or in the lagoon may have unexpected effects.
The reef is also divided up in many ways in time and space. Some animals may never meet because they come out at different times. Sunrise and sunset are times when there are many changes in what is out and what is resting. Some species gather together and travel as a group; others keep to one territory and chase away any intruders. Since space is hard to find, there may be several layers of plants and animals, with each one growing on the other.
All this means that any change in the system, like fishermen catching many of one kind of fish, can have effects all through the system, which may be vulnerable in ways that do not seem evident at first. If too much of any one kind is taken away, a balance may be upset, and it may be replaced by something else which may be less useful or desirable. If too few of the species are left, it may simply not be able to re-establish itself in the face of competition from other species (or from man). On certain reefs where the corals were killed, their place was taken by soft corals which provide less food and shelter. One kind of giant clam was fished to extinction in Tonga, and sea turtles have all but disappeared from many areas.
Successful fisheries management in tropical coastal waters depends on a detailed local knowledge of the kinds of fish and their behavior. In areas where people have fished for hundreds of years, this knowledge has accumulated and has been used to establish various traditional fishing rules and practices. It is often when this knowledge is forgotten or ignored that the fish resources are damaged.
It is essential that both the methods used for fishing and the other human activities along the shore must not hurt the ability of the coastal waters to produce food and shelter for the fish. If there is less food, or fewer places for fish to hide, there will be fewer fish.
Some fishing methods are very destructive, but they are still used because they are easy or do not require much knowledge and skill. Breaking up the coral with hammers and bars to get the fish hiding inside can ruin shallow reef areas. Using dynamite or other explosives for fishing is quick and easy, but it kills everything and reduces the corals to a heap of rubble. A dynamited reef can only be fished once; afterwards there is not much left worth catching. Too many fishermen have also been killed or injured with their own explosives. The use of poisons such as Derris root can also kill much more than the fisherman needs. Where such poisons were known traditionally, they were generally used in moderation or where no alternative was available. Modern household chemicals such as chlorine bleach also kill everything they touch, and thus kill not only the fish, but their food and the baby fish of the next generation. An area that has been poisoned will recover very slowly. The more recent use of pesticides and other poisonous chemicals for fishing can be as dangerous for the fisherman (and his family) as for the fish, as these poisons can stay in the fish and make anyone who eats them sick.
Many other things that people do can also hurt coastal fisheries. Dredging coral, filling, or building structures along the shore can change or destroy the natural areas where fish live and feed. If the land is cleared and heavy rains wash the soil down into the water, the muddy water will keep light from reaching the plants on the bottom so they can no longer make food, and as the sediment settles out it can smother and bury the corals and other animals. Pollution from cities or villages can upset the balance of life in the coastal waters, and the fish and shellfish may take up all sorts of disease germs which can make anyone who eats them sick. Industries also can pollute coastal waters with chemicals, sediment or heat that will hurt local fisheries. Even dropping anchor frequently on a coral reef can break up the corals and reduce the reef productivity.
An essential part of fisheries management is controlling how much fishing is allowed in each area and for each species over each period of time, so that the catch is not more than the area or species can replace. This means knowing how quickly a species can replace itself, over what area the replacement takes place, and how many adult fish are needed to keep up the level of reproduction. It may also be necessary to know what size fish are the best breeders (or if one size is male while another is female), and where breeding takes place. Some fish may have a particular time or place for breeding when they are particularly vulnerable, and where any fishing will have a disastrous effect on their reproduction.
This kind of knowledge or an approximation of it has often been accumulated by traditional fishermen over generations, and is reflected in their fisheries management. In the absence of scientific studies, such traditional knowledge may be the best guide to fisheries management.
It is a common error for an outsider to come in and be struck by the large number of fish in an area. His first reaction is often that those fish are a resource going to waste. However, it is not the number of fish but the rate at which they can replace themselves that is the real resource. Catching all the fish with some new technique may simply mean that there will be no fish left.
A certain number of fish can usually be caught without affecting the population. When more than that is taken, the number of fish may drop very quickly. The wise fisherman learns to recognize the signs of overfishing and knows when to stop catching that species so that it can recover. There may also be times when a fish population may already be under stress from some natural cause (bad weather, shortage of food, etc.) making it even more vulnerable to overfishing.
The evidence suggests that most tropical subsistence fisheries probably already use their shallow coastal fish resources at close to their biggest sustainable catch. There is thus little possibility of fisheries "development" in such areas without going offshore or into deeper waters. It is difficult to find an example of a commercial tropical shallow water fishery that has not led to overfishing and a decline in local subsistence resources. People for whom their local catch is an important food resource would do well to manage their coastal fishery to maintain their food supply, and not try to develop it as a source of cash income.
The ways in which a coastal fishery can be managed will depend on the laws and customs of each area. The measures taken to manage fishing must have some possibility of being enforced, either by the traditional authorities or the government. Some decisions taken within a community can be enforced by community pressure on its members. The fear of disapproval or condemnation by one's friends and neighbors can be a powerful deterrent within a community, but is less effective for outsiders. In any case, a regulation that is understood and accepted by the members of a community has a much better chance of working than one that is simply imposed by the authorities.
The laws of most developed countries do not recognize private or community ownership in coastal waters; the seashore and everything below high water mark usually belong to the government and are open to the public. When everyone has a right to go fishing, it is hard to control the amount of fishing. Each fisherman tries to catch as much as he can, because if he does not catch all the fish, someone else will. It is not possible to decide to leave some for the next time. The traditional way in many places was different. Families or villages owned parts of the reef and lagoon, and anyone wanting to fish there had to have permission. This ownership of the coastal waters or of the right to fish there limited the number of fishermen and gave them the responsibility to take care of the resource. The fishermen knew their area well, and could decide to protect certain fish or fishing grounds if necessary. To the extent that local laws permit, this can be one of the best ways to manage a fishery.
Many fish have a reproductive season when they produce the baby fish that replace those that have died or been caught. It may be easier to catch them when they are reproducing, but catching or disturbing them at that time will prevent them from replacing themselves. Protecting the ability of the fish to produce many babies is one important way of ensuring there will always be enough fish to catch. This can be done by establishing a closed season when no fishing for that kind of fish is allowed during the time it is reproducing. This was often done in traditional fisheries management through rules or taboos which allowed fishing for some species only at certain times of the year.
A fish population may also be seriously reduced, either by natural causes such as a cyclone or unusual conditions, or by overfishing. Prohibiting fishing for that species for a period of time will allow it to recover to its former numbers.
It is also possible to protect certain places that are important for the fish. Some kinds of fish have a special place, perhaps in a lagoon or mangrove swamp, where they go to reproduce or lay their eggs, or where the young fish live while they are growing up. Protecting these places from fishing or from being damaged by development will help to protect the fishing all along the coast. A part of the lagoon or reef that is protected and where no fishing is allowed can serve fisheries management in another way. Fish that live in the protected area will grow large and will produce many babies. The young fish will move out of the protected area to find a place to live, and will thus help to keep the rest of the coastal waters stocked with fish where fishermen can catch them. Making a protected area can thus help to make the fishing better elsewhere.
Protected areas are nothing new. In former times some areas were protected because they were too hard to reach in canoes without motors. Other areas were sacred or taboo, and no fishing was allowed. Today, many countries are creating marine parks or reserves both for fisheries management and to protect places tourists like to visit.
Some countries have created rotating reserves where fishing on the reef is very heavy. A part of the reef is closed to fishing for several years to allow the fish populations to recover. Then the first area is opened again and a second is closed to let it "rest" and regenerate. A few years later it is the turn of a third area to be closed, and then the process starts over again.
Another way to control fishing in areas where overfishing is a problem is to limit or prohibit certain fishing techniques. Many areas have banned spearguns because with them it is easy to kill all the big predatory fish on the reef such as snappers, groupers and emperors, to the point that there are hardly any left to reproduce and replace those that are taken. Prohibiting the taking of lobsters or crayfish with scuba diving gear protects those animals that live in deeper water. Nets with a small mesh size will catch not only the large fish, but also many small fish of little interest which should be left to grow bigger. By allowing only larger mesh nets, it is possible to permit the catch of the larger fish while letting the small ones go free. Prohibiting all fishing with explosives and poisons is important to protect the whole fishery; such destructive fishing is already illegal in most countries.
Another common fisheries management approach is to limit the number or size of fish or other animals that can be caught. Catch limits which allow a fisherman to catch or to have in his possession only a certain number of fish each day help to keep some fishermen from taking more than their share and to keep the total catch within safe limits. Size limits make it illegal to take fish or shellfish of less than a certain size, usually related to the size at which the fish start breeding. Occasionally the largest fish or animals may also be protected, as with the crocodiles in Papua New Guinea, since they may be the best breeders. Size limits are generally designed to ensure that there are enough fish reproducing to maintain the population, and to give the young fish a chance to grow up. It can also be made illegal to catch breeding females or those carrying eggs or young, as is often done with lobsters and crayfish.
Such fisheries management measures were common in traditional cultures, and were often enforced through traditional beliefs and taboos. Today it is more often the government that takes such measures through laws and regulations. However, there is nothing to prevent a tribe or village that has control of its coastal waters from managing its own fishery. Any management measures have more chance of working if they are understood and appreciated by the local fishermen and if they are supported by group pressure as well as punishment. It is hard, particularly in island cultures, to go against the views of one's family and friends and to risk criticism in the local community. Such pressure is the best way to stop those who fish with dynamite or poisons because they are quick and easy ways to get a large catch (generally to share with family and friends). If everyone realizes that good fisheries management is in the interest of the whole community, and everyone works to make it effective, then the chances are good that the community will continue to have a good supply of fish long into the future.
Is fishing more like farming or like hunting? Why?
What do fish need in order to live?
Why is fish reproduction important?
What are different ways that fish or shellfish ensure that those that are caught or lost are replaced?
Why are coral reefs and other tropical ecosystems so complicated?
What can happen if fishermen catch almost all of one kind of fish?
Do you know of examples of over-fishing in your own area?
Is protecting the fish enough, or are there other things to protect in coastal waters to keep the fishery productive?
Why is breaking coral or fishing with dynamite or poison bad for a reef?
What are some of the techniques that can be used to manage a fishery?
Are traditional fisheries management measures still observed in your area?
What do you think needs to be done so that there will always be enough fish to catch?
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