by/par
J. Vostradovsky
Fisheries Research Institute
Research Station for Dam-Reservoir and River Fisheries
VÚRH - Zitná 13, 110 00 Prague 1
Czechoslovakia/Tchécoslovaquie
ABSTRACT
A tagging experiment to determine the distribution of fish in the Lipno Reservoir was carried out over a five-year period and the results used to assess the applicability of the method for evaluation of stock magnitude. Most species showed a well defined territorial instinct, returning to and staying at the place of their original capture for most of their lives. It is concluded that the behaviour makes the use of such mark-recapture method difficult for the determination of absolute population density in such large reservoirs, although estimates in limited areas may be reliably obtained in this way.
RESUME
Une expérimentation de marquage afin de déterminer la distribution du poisson du réservoir de Lipno a été effectuée sur une période de cinq ans et les résultats ont été utilisés pour s'assurer de l'applicabilité de la méthode pour l'évaluation de la magnitude du stock. La plupart des espèces ont fait preuve d'un instinct territorial bien défini, retournant et restant au lieu de leur première capture pour la plus grande partie de leur vie. On en conclut que ce comportement rend l'utilisation de cette méthode de marque- recapture difficile pour déterminer la densité absolue de la population d'aussi grands réservoirs bien que l'on puisse se fier à l'évaluation de zones restreintes effectuée de cette façon.
CONTENTS
1. INTRODUCTION
2. METHODS
2.1 The Site
2.2 The Composition of Fish Stock
2.3 The Development of the Conditions of the Site
2.4 Organization of the Experiment
3. RESULTS
3.1 Carp - Cyprinus carpio
3.2 Bream - Abramis brama
3.3 Tench - Tinca tinca
3.4 Perch - Perca fluviatilis, pike - Esox lucius,
pike-perch - Stizostedion lucioperca
4. CONCLUSIONS
REFERENCES
In order to evaluate the recapture rate of some fishes released in the Lipno Reservoir (upper course of the Vltava in southern Bohemia), a five-year experiment was performed with tagged fish. Its purpose, among other things, was to gain information on the horizontal distribution of fish in the reservoir and to use the findings for the evaluation of the magnitude of the fish stock.
The Lipno Reservoir, on the upper course of the Vltava (tributary to the Elbe), was completed in 1959 for hydro-power. The average depth is 6 m, the maximum depth 20.5 m, the maximum area 4 650 hectares, and the length of the reservoir 36 km. The altitude is 700 m above sea level. Sport fishing is practised in the reservoir, together with a commercial fishery.
Fishes capable of adaptation to the change of conditions (from reophilic to limnophilic) remained in the stock (pike - Esox lucius, perch - Perca fluviatilis, roach - Rutilus rutilus, bream - Abramis brama, and some others). Carp (Cyprinus carpio) is stocked at the rate of about 100 K1 and K2 fish per hectare annually, with an annual recapture rate of about 6 fish per hectare.
The development of the site was typical of new reservoirs: high productivity at the first stage, multiplication of phytophagous fishes and their gradual decrease in the subsequent years (negative effect of winter fluctuation of water level, low stock in spring in the time of reproduction).
An experiment was organized within the five-year scheme for the observation of individually tagged fish. Besides the distribution of fish in space and time, we also evaluated the applicability of the results to the estimation of the abundance of the fish stock. Twenty- three thousand and twenty-six individuals of the main species (carp, bream, tench, perch, pike, pike-perch) were tagged. The campaign enjoyed great publicity by the mass media (posters, press, television, radio). Rewards were given for tags returned with the data on the fish, and a lottery was organized for those who returned tags. Using a Monelmetal wire, celluloid tags were fitted to the spiny rays of the dorsal fin; acetate cellulose seals were fixed to the muscles under the bone supports with a silon (monofilament) thread. The methodical problems have already been described in detail by Vostradovsky and Vostradovská (1971).
During the experiment, we succeded in tagging 16 639 carp. A large proportion of this number came from ponds (76 percent), and a smaller part was fished directly in the reservoir. Most of the fish belonged to the size group from 161 to 280 mm (most frequently up to the weight of 800 g). The fish were released in the upper, central and lower parts of the reservoir. The total recapture rate from this reservoir was 16.57 percent in carp (angling and net fishing shared 50 percent of the recaptures). Maximum recapture values were recorded from the one-year portion of the released and tagged fish in the same year or in the sub- sequent year. The recapture rate showed a rapid decrease in subsequent years. The fish needed a greater lapse of time to move from the site of release to a distance greater than 15 km (only 7 percent of the recaptured fish got to this distance within the first half-year after release). On the other hand, 15 percent of fish were recaptured from a smaller distance (1 km), within one week. It is clear from this that uniform releasing of fish throughout the reservoir is needed for population estimates of this species. Although the dispersion of the released tagged fish increases with time, the number of total recaptures decreases. In addition, the release of a large number of tagged carp in one place cannot be recommended as such fish stay together in a shoal. Carp reared in side reservoirs tend to stay near the outflow from the appropriate reservoir and higher recapture rate is thus obtained of fish from the reservoir than of fish transported from a different environment. It follows from this that it is necessary to tag autochtonous fish populations. It can be stated, in conclusion, that local shoals are formed in the reservoir and that these move away from the place of release only after several months.
In this experiment 3 460 fish, mostly 181–260 mm in size (up to the weight of 400 g) were used for tagging. The total recapture rate of tagged fish reached 10 percent. It can be inferred from the data on horizontal distribution that bream is a species with a well developed homing instinct. Similar findings are reported also by Stott et al., 1963, for another species of the same family. Eighty-eight percent of fish stayed within 1 km of the site of capture and release. The fish artificially transferred to another place in the reservoir moved toward the original area of capture and were supposedly caught on the way back to the area if they were not already inside it. Throughout the period of observation they lived in the place where they were originally captured and this will probably be the case throughout their life. With respect to the practical implications of this finding, it is necessary to carry out thorough fishing in as many places as possible within the reservoir for estimations, and to release tagged fish in these same places. On the other hand, repeated netting and angling in the same place may lead to local over-fishing; this may manifest itself as a reduction in catch (which may, in turn, lead us wrongly to believe that the fish stock is reduced throughout the area - repopulation apparently requires a considerable time.
It can be stated in conclusion that bream, living in the artificial lake, form local shoals born, growing, maturing and reproducing within a limited territory. There are very many such shoals along the bank. This is true even of the largest reservoirs, as indicated by findings from the U.S.S.R., reported for instance by Sharonov (1966), Poddubnyi (1966), Austrauskas (1971).
The total number of fish tagged was 901. Eighty percent of the fish belonged to the group up to 200 mm (200 g). The highest recapture rate was found in the largest fish, belonging to the size group from 301 to 360 mm (61 percent). The total recapture rate was 7 percent (recapture values were decreased by a high proportion of tagged fish of smaller size). Most of the fish were returned from the places where they were caught (coming from the reservoir) or from the places of first release (fish coming from ponds). Only in one case, a female tench was captured 49 km from the dam in the river over the reservoir (the longest migration of all the tagged fish species). Summing up the results, we must state that this species stays mostly in the place of preceding capture or release.
The total number of 1 358 fish of these three species were tagged and home territory and the homing instinct were also observed in them. A highly developed territorial character is typical even of pike which can often be found in the same place several years in succession. The total recapture rate reached 18 percent in perch, 31 percent in pike, and and 9 percent in pike-perch. The greater size of perch and pike-perch was also an important factor underlying recapture. For instance, perch heavier than 400 g showed a recapture rate of 30 percent. Only in pike was the highest recapture rate observed in fish up to the weight of 2 000 g (the proportion of the fish of this size in the total recapture rate was 77 percent, whereas heavier fish represented only 23 percent). In addition, 84 percent were recaptured in almost the same place as the site of release (i.e. within 3 km). Only in spring were several individuals observed to move to a distance greater than 10 km but still less than 20 km; this may be ascribed to the low water level at the time of reproduction and, consequently, to the need for seeking more suitable spawning places; the shock of tagging may be another cause. The high recapture rates of this typical predatory fish correspond to the findings reported by Carbine and Applegate (1946). Pike moving to a distance greater than 3 km showed higher daily gains in weight than resident pike; this was ascribed to greater opportunity of contact with prey. Again, it is necessary to fish thoroughly in as many places in the reservoir as possible, if these findings are to be useful for realistic estimates.
Similar findings were obtained for pike-perch. The fact that this species maintains a home territory is indirectly mentioned by Goubier (1969) and is further indicated by the catches of this fish in the place where they were released.
The majority of fish showed a tendency to stay in one place either for a varying period of time (e.g., carp) or throughout their life (e.g., bream). The homing instinct, the home territory and the high number of local shoals along the bank characterize the movement- behaviour of fish populations in the reservoir. Although it is possible to use individual fish tagging for the estimation of the total size of the fish stock, it is very difficult from the technical point of view. It requires considerable effort for uniform fishing of the material for tagging along the entire bank of the reservoir, and in some cases, such thorough fishing is impossible due to the configuration of the banks and bottom. In addition, only a short period of time is available for such an effort. Areas smaller than that used in this trial are better for detailed determinations. Such determinations are easier for one species than for another and the lowest effect is obtained if the trial is performed in all the fish stock at the same time. Bream may be advantageous from this viewpoint as it has a well developed homing instinct from birth to the time of sexual maturity and stays in the same place throughout its life, or even returns to that place if transferred within the water body.
Where researchers want to collect tags from fish captured by anglers or fishermen, publicity and organized tag collection with material stimuli are as important as, for instance, the research method or the technical equipment.
