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Tuatara: Volume 2, Issue 2, July 1949

Problems of Marine and Freshwater Fisheries Biology in New Zealand

page 53

Problems of Marine and Freshwater Fisheries Biology in New Zealand

Although fisheries biology is one of the most recently developed branches of applied biology, it is one which is now showing considerable activity in many countries. Prior to the 1914-18 war valuable foundations had been laid, but this had been done largely by university workers, sometimes with Government subsidies, and the official organizations set up for the specific purpose of conducting fisheries research were few and small. The decreasing yields which many commercial fisheries were showing in relation to the fishing effort expended was already drawing increasing popular attention to the need for research into the basis of the fisheries, and this was emphasised in many cases by the recovery which was found to have occurred as a result of the temporary cessation of fishing caused by the war. This led, in the period between the wars, to a rapid expansion of activity in fishery research; an expansion which has continued since the last war, and has recently received additional stimulus from the realization of the drastic need to develop the world's food resources to keep pace with the increasing population.

In New Zealand some research on aquatic biology, particularly as regards the taxonomy and life history of various freshwater and marine animals and plants had been carried on from an early date, but it was not until the late 1920′s that organized research into the particular problems of fisheries biology was commenced. The appointment of an experienced fisheries biologist as Chief Inspector of Fisheries led the way to the gradual building up by the Marine Department of an organization for research in sea fisheries. At about the same time the combined Acclimatization Societies, which are responsible for the local administration of freshwater fisheries in New Zealand, set up a permanent Research Committee and engaged qualified research staff. This Organization was incorporated into the Fisheries Branch of the Marine Department in 1937. At the present time all fundamental fisheries research is being carried out by the Marine Department, although in the freshwater field interested bodies are encouraged to carry out local investigations, while active and valuable co–operation is being maintained with University departments in both fields of work. The Department's present, though inadequate, staff of six scientists and a number of assistants is housed in a well–equipped laboratory in Wellington, although work is undertaken in the field and at sea whenever there are problems to be investigated and a small research vessel is permanently maintained in the Auckland area.

page 54

Problems in New Zealand's freshwater fisheries are somewhat simplified by the relatively small number of species involved. The native freshwater fish fauna is limited to rather more than twenty species belonging to six families. With the exception of the eels they are all small and none are of any sporting value. Consequently many other species were introduced from Europe or America in attempts to establish sporting or commercial fisheries. Only three of these have become of widespread sporting or commercial interest. These are the Brown trout (Salmo trutta), the Rainbow trout (S. gairdnerii) and the Quinnat salmon (Oncorhynchus tshawytscha). The limited resources available for freshwater fisheries research have therefore to be concentrated upon these introduced fish and upon three native species. These are the eels Anguilla dieffenbachii and A. australis schmidtii which are of potential commercial value on account of their abundance and relatively large size, and the migratory Galaxias attenuatus which supports the whitebait industry which yielded over 300 tons in 1947.

Fisheries biology is fundamentally a branch of quantitative ecology, being concerned with determining the factors which control the output of the fisheries, and, where possible, with finding means of maintaining it at the highest possible level. This requires in the first place a knowledge of the fundamental biology of the species concerned, including particularly their systematics, distribution and migrations, rate of growth, reproduction, predators, and feeding habits. These provide a basis from which research can be undertaken on the quantitative effects of these various factors upon the population and the correlation between them and the crop taken by man. The introduced fish of New Zealand have been the subject of much research both in their native lands and in other countries to which they have been introduced, and consequently general knowledge of their biology is well–advanced. In these circumstances the problems concerning these fish which are of greatest interest are those produced by local conditions and those involving the quantitative relations between the fish populations and their environment.

Trout and salmon are typically inhabitants of the rapid rivers of hilly country and are therefore in many ways adapted to withstanding the effects of floods. New Zealand is a geologically young country and consequently erosion of the high lands and changes of river–bed level are still proceeding rapidly apart from any recent man–made acceleration. The resulting instability of river beds renders flood effects particularly severe here, and the investigation of them as a potential limiting factor for fish populations presents interesting and pressing problems. The possible adverse effects are two; trout feed largely upon insect larvae and nymphs which live among the stones of the river bed and are easily destroyed by the disturbance of the bed in a flood; direct destruction of fish may also occur particularly during the three or four months which the eggs and larval fish spend buried in the gravel before the active, swimming stage is reached. Preliminary work has shown page 55 that both effects may at times be serious; well over 90% of the bottom fauna has been found to be destroyed in a single flood. Detailed studies of the extent of damage caused by floods of varying magnitude on different types of bed, and correlation of the results with records of flood frequency are still needed before the extent to which these factors may be limiting fish stocks can be determined.

Apart from its potential commercial value the long–finned eel (A. dieffenbachii) is of special interest as a predator on and competitor for food with the introduced fishes. This interest is increased by the relative ease with which its numbers can, in some cases, be controlled. The complex relationship between the various species will however require detailed study before the value of eel–control activities can be determined. Since this eel is a native species we cannot draw on overseas work for knowledge of even its general biology. This phase has however now been fairly fully studied, and quantitative investigations of the size and composition of eel populations are now being undertaken.

Another native predator on fish which presents somewhat similar problems, but which has been even less studied, is the Black Shag (Phalacrocorax carbo).

The other native fish of direct practical importance, the whitebait, remains unfortunately still in the stage in which only the barest outline of its biology is known, and many questions of the greatest importance remain to be answered before any measures for the improvement or maintenance of the crop can be based on sound biological grounds. The remaining species have at present little practical importance except in their relation to the introduced species either as competitors for food, or as food themselves. They present however an almost untouched field to the aquatic biologist and even their systematics, which must be worked out to provide a sound basis for ecological studies, is still in a fragmentary state.

The development of additional freshwater fisheries in New Zealand must depend upon the introduction of further valuable species suited to environments which have proved unsatisfactory for salmonids. In the sea, on the other hand, we have a great number of species many of which are almost unknown from the fisheries angle.

At present the magnitude of the problems connected with marine fisheries already worked makes it necessary to confine present work to some extent to the economic management of grounds already known, rather than the exploration of new resources. However, much work may have direct or indirect application in both directions.

Very little of the essential biological knowledge has been recorded for our New Zealand marine fishes. There are, in fact, a whole series of investigations needed, each of which could well occupy a team of page 56 research workers. Much of this work is, of course, of interest to pure as well as applied biologists, and there are indeed many in the universities and museums who are directing their attention to fundamental marine problems. However, the applied worker must at present to some extent do without the groundwork of accumulated knowledge, each section being sought for as required.

Many of the classifications now in use need to be brought up to date and related to those used overseas; a manual of New Zealand fish is badly needed. Further, the races and clines formed within the different species, and the migratory patterns, must be determined, particularly for the more important food–fishes such as the snapper, tarakihi, hapuku, and blue cod.

The available sources of fish–food, both benthic and pelagic must be plotted quantitatively and the ensuing ecological problems studied. Closely coupled with this comes the physical composition of the sea, its currents, temperatures, salinities, and the other mineral contents.

Life histories of nearly all our fish must be studied. We must be able to recognise eggs and larvae at all stages, while in the older fish rates of growth and changes of condition must be observed and analysed.

With the great advances being made throughout the world to–day in marine biological equipment and technique, the biologist must often become a technician, adapting the specifications of overseas equipment which is often not available here, or evolving new designs for his own requirements.

Of the more specific problems which arise from the commercial fisheries, one receiving a considerable amount of attention at the moment is the trawl and Danish seine fishery which supplies nearly 70% of the landed commercial catch. Many of the trawling grounds at present in use are being fished to capacity, some are being over–fished. One, the Hauraki Gulf, has been so seriously depleted that it has dropped from being our most productive to such a low level that a trawler working in Auckland waters is a rare sight to–day. Immediate remedial measures may be taken by restricting exploitation, but the fundamental causes must be studied, and the lesson applied elsewhere before it is too late. New fishing grounds may yet be available, further from the coast, but little is known as yet of the seas beyond our continental shelf, although a few more venturesome fishermen have explored the edges.

Pelagic species, as yet little exploited, may possibly form the basis for future fisheries, but here again questions arise. Are these fish regular enough in occurrence to support an industry? If they are taken will an important source of food be lost for the fish already being caught?

To study fish one must have boats. The sixty–foot research ship “Ikatere,” stationed at Auckland, is equipped as a motor trawler, and page 57 has recently been mainly employed investigating the selectivity of trawling gear of different mesh–sizes, although some preliminary plankton and sea–bottom surveys have also been completed. However, the fishing industry can not always be studied from a departmental boat. One must see how the fishermen themselves work. These men are not scientists but their practical knowledge can be tapped by a practical scientist, even if he must for the time discard the Linnean nomenclature for somewhat saltier terms. Many fishermen in fact become almost embarrassingly active in supplying information or sending new “wogs” to the laboratory.

Not all the work is at sea—some fisheries products, notably the toheroa and rock oyster, may be studied on dry land. Last year an intensive study was made of the toheroa populations of the North Island, bringing many interesting questions to light. Why have these shellfish disappeared so suddenly from Ninety–mile Beach? We have some reason to believe that they may return just as suddenly, and that similar movements on a smaller scale are occurring on other beaches.

To the biologist straight from the dissecting bench there is something unfamiliar in the study, not of individual fish, but of fish populations. The process may be tedious at first when there are hundreds of fish to be measured, hundreds of water temperatures to be taken, or hundreds of otoliths or scales to be removed. Back in the laboratory there is the same multiplicity of figures in length frequency analysis, water circulation charts, or age determinations. There is, however, always some interesting sideline, an unfamiliar species coming to the surface or an arresting phase of ecology; even the routine data gain charm as they arrange themselves into a pattern just as fascinating as the most complex dissection.