To date the history of man’s exploitation of fish resources makes dismal reading. Almost the first records which exist about fisheries are these concerning the decline in the yield from one fishery or another. The record continues today. However, it was not until the 19th century that a combination of factors led to the start of fisheries science. In the second half of the 19th century the North Sea plaice fisheries were in a poor state. Increasing fishing effort was not resulting in larger catches, catch-per-unit effort was falling and the average weight of plaice in the catches was declining. It was showing all the signs of what, in today’s terms, is called “over-fishing”. However, fisheries had collapsed in the past without it initiating research. But the same factors that were leading to over-fishing, industrialization and advanced technology, were also providing the money to pay scientists to investigate the reasons for the collapse. As a result numerous public enquiries were held, mainly in Great Britain, to collect information which would provide an answer to the question of why the North Sea plaice stocks had declined and to determine what could be done to rectify the situation. This was the birth of fisheries science.
Once the statistics of a few fisheries had been examined it was soon realized that they showed a picture common to all. (Fig.1.1). As total fishing effort increased with time total catch rose initially, reached a maximum and then flattened out, or even sometimes to much less than had been obtained at low levels of fishing effort. At the same time, both the catch-per-unit effort and the mean weight of the individual fish in the catch declined continuously. While it is clear that the basic reason for this is quite simple - too many fish were being caught, - in any particular fishery a detailed analysis is necessary to determine how many fish (and of what size) should be caught each year to assess the future of the fishery. This analysis depends on having the right sort of information, most of which can be obtained from the fishery itself.
On the face of it, the history of man's exploitation has been one of success with catches rising at 7% a year since 1950 but this success is more apparent than real. The increase in catches has been obtained mainly by exploiting one virgin stock after another in succession, leaving a series of depleted stocks incapable of giving their best yields. This cannot continue indefinitely, ways must be found of controlling fishing.
The normal sequence of events in an uncontrolled fishery is that the increase in the number of fishing units usually stops because the catch-per-unit effort falls to such a low level that it becomes uneconomic to build any more. Often the number decreases as the least economic vessels are withdrawn from the fishery and the more mobile vessels, such as factory trawlers and freezers, move on to fish other stocks. It is unusual for the fishery to collapse completely (Course A in Fig. 1.1) unless the fishery has had some severe biological effect on the fish, such as reducing the breeding stock to such a low level that recruitment almost ceases; one such example is the English East Anglian herring fishery. Assuming this does not happen the fishery stabilizes at the levels shown by B on each curve in Fig. 1.1. This is far from an ideal situation; the total catch is much less than the maximum obtainable and the fishing effort required to take it is high and therefore uneconomic. If the catch-per-unit effort rises sufficiently it may attract back some of the mobile vessels and the fishery then oscillates.
The obvious objective is to reverse the sequence of events and stabilize the fishery either at some point C, near but beyond the optimum, or at point D, at which the maximum total catch is being taken, or at point E at which less than the maximum total catch is being taken but it is being taken most economically. Before decisions can be made as to how any of these objectives are to be realized, the factors underlying the shape of these curves must be determined.
Before discussing this point it is important to consider the role of the fisheries scientist. The majority of fisheries are international and many of them are regulated by international commissions, which either regulate all the stocks in a given area or certain species. Examples of the former are the Northeast Atlantic Fisheries Commission (NEAFC) and the International Commission for the Northwest Atlantic Fisheries (ICNAF), which between them regulate fishing in much of the North Atlantic, and an example of the latter is the Pacific Halibut Commission which regulates the fishery for that one stock of halibut. All nations which fish the stocks in a commission's area or the stock, in the case of a single species commission, should be represented upon it if it is to be effective and they usually are.
The fisheries scientists present their data to the commissions but the scientists do not make the final decisions upon regulations. These are made by administrators and politicians both of whom take account of national as well as international interest. It has been a feature of regulations within fisheries commissions that short-term national interests tend to outweigh longer terms, or international interests. This tendency is increased if the scientific advice is uncertain or inconclusive. The history of the International Whaling Commission is a classic example.
Thus the fisheries scientist not only has his responsibility to collect data so that he can advice but also the responsibility to collect his data in the best possible manner so that he can advise with confidence and precision. Because a fishery fluctuates from year to year he also needs to monitor it, up-date his assessments and continue his research into improving his methods.
Before a fisheries scientist can even start giving advice he must know what information he must collect in order to describe his fishery. A series of investigations are involved, for many of which the fishery provides the data.
These data are provided by the fishery and are often the only data available. Records of total catches are usually available long before any other information because the information about the catch, and its value, are important for economic reasons. However, catch tells us little about the state of the fishery; as shown in Fig. 1.1 the same total catch could be taken from an underfished as well as an overfished stock. To have a real understanding of the fishery some measure of fishing effort is required. It is not always easy to collect a meaningful index of fishing effort but sometimes quite orude estimates will suffice.
The other data provided by the fishery are length compositions and, but not always, age data. However, catches are usually very large; for examples the number of anchoveta caught by Peruvian ships in a year may be more than 10,000,000,000. It is impossible to measure all these and a sampling system needs to be devised so that the measurements of a few fish provide reliable information about the total catch. If a good statistical system is used to sample the catches and the samples taken in accordance with a prescribed pattern then the characteristics of the population (for example, the length distribution of Peruvian anchoveta) can be estimated to any desired level of precision.
Certain investigations have to be done by the fisheries scientist. Of these the determination of the stock structure is the most important because it is essential to link catches with the fish stock from which they are taken. This is usually determined by tagging or less usually by some other method, such as the study of meristic character.
The fish is also part of its environment and reacts to it when migrating so studies of currents are important. In up-welling areas the pattern of the current systems can have a decisive effect upon the fishery. The physical and chemical characteristics of the currents also determine to a large extent the basic productivity of a region upon which the ultimate sizes of the stocks depend. The study of phytoplankton, zooplankton and the feeding of fish are all links in this chain even though studies to date have been of little use in helping to solve fisheries problems.
To put all this information to use methods of population dynamics are required to enable the fisheries scientist to answer the questions posed by the exploitation of a fishery, which were outlined earlier. Population dynamics depends upon building models which describe the fishery and allow prediction. Given accurate data the better the model the more correct the prediction will be.
This series of studies described in sections 1.5.1 to 1.5.4 are the basic building blocks of any fisheries investigation and this manual provides an introduction to the main ways in which these studies are conducted. No section is comprehensive, because each is intended to lead on to further study on each topic, but each is designed to show what methods of research are available and how this research should best be conducted to enable the fisheries scientist to meet his objectives. According to Gulland (1971) the yield from the traditional bony-fish resources is nearly at its estimated maximum level of 100,000,000 tons a year and there are few unexploited stocks to develop. For further expansion we shall then be dependent upon non-traditional resources, such as krill. In this situation we are even more obliged to exploit our traditional fisheries resources in the best manner possible. To do this the fisheries scientist must play a major rôle.
Gulland J.A. 1971, The fish resources of the ocean. Fishing News (Books) Ltd., London, 255 p.
Fig1.1 Generalised history of fishery