by
B. Steinmetz 1
National Correspondent
I FISHERY BIOLOGY AND MANAGEMENT
Administration and policy
The fishing rights for eel are in the Netherlands in general rented by commercial fishermen, whereas those for other (scale) -mainly coarsefish are in hands of the sport. The national organizations of both groups came to a compromise that was adopted by the Minister of Agriculture and Fisheries as an element for future inland fisheries policy. On the following main points, which asked for an amendment of the Fishery Law (1963), there was agreement.
The two National Angling Organizations expressed as their intentions (1) to bring in the commercial fishermen in the management by regional and local organizations of their fish stocks and (2) to accept a commercial fishery as far as that does not detoriate this management. Moreover the sport was in favour of a governmental policy focused on the diminuation of specialized eel fishing by the sport.
A severe drop -21%- in the number of licenses issued to sport fishermen from 913.000 in 1983/84 to almost 713.000 in 1984/85 had to be faced in the first year without a closed season. A national poll for reasons indicate that sport fishermen with a low fishing frequency partly stopped. (It concerned especially youth (< 25 year)). The others continued but with a lower frequency (83/84-33 times per year; 84/85-26x).
With the organization of commercial fishermen of Lake IJssel negotiations were held to stabilize and restrict the fyke fishery (see I.2).
1 Directorate of Fisheries, P.O. Box 20401, 2500 EK Den Haag, Netherlands.
Research
In Lake IJssel -200.000 ha.- research by the Netherlands Institute for Fishery Research (RIVO) revealed that the production of pike-perch is far below the possibilities, due to a too low legal size and high losses of 0+ fish in fykes. Technical measures developped till now, proved to be not successful.
In the lower course of the Rhine and Meuse large scale tagging experiments with roach and pike-perch were held by the same institute. The results indicate that migration is limited, whereas the fishing intensity by sport and commercial fishermen was up to 25 percent, but in general lower.
Special attention by different research institutes is paid to pike-perch as an instrument in ichthyo-eutrofication. The Organization for the Improvement of Inland Fisheries (OVB) started with the evaluation of artificially propagated pike-perch fingerlings. Fingerlings of three sizes (15 mm, 25 mm and 35 mm) have been subject to trials in drainable ponds.
In future studies attention will also be paid to date and place of stocking and density on the survival.
The University of Wageningen (LH) studied the interrelations between pike-perch, bream and fishfood organism (plancton and benthos) in four great lakes, among other things to develop criteria for a quick appraisal of the year to year situation.
The OVB finished the evaluation study of grasscarp. It was found that the waterweed control measures adversely effect pike, which was used as indicator species. The experiments aimed at the formulation of stocking guidelines for “carp-pond” fisheries were completed. A report will be published soon.
Research by the RIVO on eel was focused on glass-eel immigration -which diminished rather sharply since 1980- and on ageing. Tagging experiments were started for the ageing study.
Management
Monitoring of fish populations for fisheries policy by the Directorate of Fisheries was continued as well as the extension to fishery managers by this Directorate and the Directorate of Outdoor Recreation responsible for angling.
Discussions with the National Organization of Commercial Fishermen lead to an agreement about the catch of 130 ton undersized eel for restocking purposes and eel culture, of which 50 tons became available (A similar agreement is in preparation for 1986).
The interest of fishery managers in the educational extension of the OVB is still growing. Until now more than 800 persons participated in the basic course; that is about 30 percent of all persons directly involved in the fishery management. Two other courses are held; one on the principles and problems of fish monitoring and another on the identification, biology and management of Dutch freshwater fish.
Participants of the course receive without further costs the OVB educational magazine just as the majority of fisheries managers.
A special Dutch problem is the fact that the boards of angling clubs needs the approval of the members for their intended fisheries management. For extension to these members until now 13 pamphlets on different topics were made.
An increase in the use of creel census for management purposes can be noticed. A small field guide “The Dutch freshwater fishes” was therefore renewed and republished by the OVB (80.000 copies).
A serie of papers was started in the journal of the Directorate of Fisheries on “how to set up a fisheries management”.
II FISH CULTURE AND DISEASES
Administration and policy
Due to the growing interest in and the need for a clear policy with regard to fish culture for consumption purposes, a note on this subject was presented to and accepted by the Parlement. In first instance the attention is focused on the production of salmonids, eel and African catfish in recirculation systems. Governmental extension for this business was set up, as well as a first and second line care for fish diseases.
Special attention was paid to the problem of glass-eel and small eel from coastal and inland waters for stocking purposes and for eel culture. An agreement about the catch of undersized eel was realised with the organization of commercial fishermen (see I.3). A further decline in the glasseel catches along the coast had to be faced.
A new eel parasite Anguillicola crassus, already found near Hamburg in 1983, was found in the Netherlands in July 1985.
Research
At the University of Wageningen (LH) the studies on African catfish (Clarias gariepinus) were continued. Attention was paid to growth differences of males and females in the weight range of 200–400 gr. in monosex and mixed populations. Males proved to grow better (ca. 39%) than females in monosex populations at a foddering level adapted in practice. In mixed populations the food conversion of both sexes proved to be better.
The results of research of the LH on the artificial propagation of A. catfish were collected in a manuel on this topic in English and French. Special work is done on the cultivation of sterile (triploïd) fish and of gynogenetic fish, as well as to the role of feromones. Research revealed that at least four steroid conjugates are produced by males of A. catfish. Experiments with synthetic steroid conjugates to attract ovulated females were started.
In close coöperation with other institutes and the industry, research is done by the LH on the commercialisation of human Chorionic Gonadotropin (hCG) for artificial propagation of fishes. Recent results revealed that this product did not bring carp to ovulation. Further research with hCG in combination with other hormones has been started.
Research results on sex determination in cows were considered in connection with A. catfish and carp. Serological research indicates that in the testis of adults of both species a special male H.Y. antigen exists, whereas this is not the case in the ovarium.
Experiments with different temperature and Artemia fodder were held with larvae of A. catfish. In ponds the effects of a carp stock and Dipterex treatments on the production of O+ pike-perch were measured. Stomach research revealed that carp is a feed competitor of bigger pike-perch juveniles (2–3 cm). With carp the pike-perch continued to eat zooplancton to a length of 4 cm, before taking chironomids. A Dipterex treatment resulted in average of 75.000 O+ pike-perches per ha. instead of 36.000 in untreated ponds.
Methods to uncleave fish eggs were studied. An industrial product of protease-maxatase-proved to be useful for A. catfish. Metabolism of embryo's and larvae were also considered.
Research on fish diseases by the LH was focused on Ruptured Gut Syndrom (RGS) in A. catfish and Nervous Syndrom (NS) in young carp.
A study of the future market of A. catfish was started by the Agricultural Economic Institute (LEI).
Management
High numbers of cormorrants visiting the fish culture station of the OVB near Lelystad caused severe losses of fish. Several methods to scare birds proved unsuccessful. The OVB started to bring an action against the State.
III WATERQUALITY AND CRITERIA
Administration and policy
For the State owned waters a draft water quality plan was finalized. Progress was made with the same plans under provincial responsibility. In both attention is paid to the E.C. guidelines for cyprinid and salmonid waters. The State-Secretary of the Ministry of Agriculture and Fisheries stated in Parlement that in principal all inland waters have a function for the life of fish and for the recreational and economic use of it. Most of the state waters should have within 3 years a “cyprinid” quality.
Research
The Institute for Inland Water Management and Waste Water Treatment in coöperation with other interested institutes and organizations started a study on Ichthyo-eutrofication. Experiments in ponds on the OVB fish culture station in Beesd with predators of different size to limit bream, roach, rudd population will be a first step.
IV PRODUCTION STATISTICS
The production of fish in farms in 1984 is given below.
| Species | Production (× 1000 kg ~ ton) for consumption* | for stocking |
| Eel | 100 | - |
| Salmonids | 200 | 185 |
| African catfish | 15 (90) | |
| Carp | - | 38 |
| Grass carp | - | 30 |
| Pike 0+ | - | 407.000 (st) |
| Pike-perch 0+ | - | 47.000 (st) |
| Other | - | 6 |
From the catches in Lake IJssel in 1984 320 ton pike-perch, 425 ton perch, 695 ton eel and 1.027 ton other coarse fish, mainly bream en roach, were sold via official markets. However fishermen are not obliged to sell their fish in this way. About 30–50 percent is sold directly to traders.
V BIBLIOGRAPHIC REFERENCES
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