M. Leopold, T. Korulozyk,
W. Nowak and L. Swierzowska
Department of Fishery Economics
Inland Fisheries Institute, Olsztyn
The two types of fyke net used in Poland both have high work requirement which make them unpopular with fishermen. The type I nets are a possible method for estimates of absolute density in the lakes in which they are used, whereas type II nets have only limited value as a measure of stocks of all species except pike. Wing nets have an equally high work requirement but are a satisfactory measure of eel stocks. The combined pound net provides valuable information on migrations within a lake and on the structure of the spawning stock.
Les deux types de verveux utilisés en Pologne sont si dificiles à manier que les pêcheurs n'aiment guère s'en servir. Les filets du premier type permettent toutefois d'évaluer la densité absolue dans les lacs où ils sont utilisés, tandis que les filets du deuxième type ne répresentent qu'un intérêt limité pour mesurer les stocks de toutes les espèces sauf le brochet. Les filets à ailes sont également très difficiles à utiliser mais permettent de mesurer tous les stocks de façon satisfaisante. Le filet-piège combiné fournit des informations intéressantes sur les migrations à l'intérieur d'un lac at sur la structure de stocks de reproducteurs.
1. TYPE I FYKE NET
1.1 General Description of Gear
1.2 Tactics of Fishing
1.3 Quantitative Characteristics of Catches
1.4 Qualitative Characteristics of Catches
1.5 Characteristics of the Intensity of Fishing
1.6 Efficiency of Type I Fyke Nets
1.7 Labour Cost of Catches
1.8 Type I Fyke Nets as a Measure of the State of Fish Stock
2. TYPE II FYKE NET
2.1 General Description of Gear
2.2 Tactics of Fishing
2.3 Quantitative Characteristics of Catches
2.4 Qualitative Characteristics of Catches
2.5 Characteristics of the Intensity of Fishing
2.6 Efficiency of Type II Fyke Nets
2.7 Labour Cost of Catches
2.8 Type II Fyke Nets as a Measure of the State of Fish Stock
3. WING NET
3.1 General Description of Gear
3.2 Tactics of Fishing
3.3 Quantitative Characteristics of Catches
3.4 Qualitative Characteristics of Catches
3.5 Characteristics of the Intensity of Fishing
3.6 Efficiency of Wing Nets
3.7 Labour Cost of Fishing
3.8 Wing Nets as a Measure of the State of Fish Stock
4. COMBINED POUND NET
4.1 General Description of Gear
4.2 Tactics of Fishing
4.3 Quantitative Characteristics of Catches
4.4 Qualitative Characteristics of Catches
4.5 Characteristics of the Intensity of Fishing
4.6 Efficiency of Combined Pound Nets
4.7 Labour Cost of Catches
4.8 Combined Pound Nets as a Measure of the State of Fish Stock
The type I fyke net consists of a conical trap with two non-return valves arranged in a line. The trap and a bag are mounted on a frame consisting of four to five circular hoops. Type I fyke nets often have additional elements, such as wings, leaders, fences, etc. They can also consist of either one or two traps; the latter type being used more frequently. The size, mesh size and size of additional elements of the net depend on the species to be caught. Lengths of trap range from 1.30–2.20 m, the diameter of the first hoop from 35–90 cm, and the mesh size varies between 25 and 35 mm; wings and leaders are generally up to 4–5 m long with mesh sizes of 28–30 mm. The most frequently used modification of the type I fyke net is the so-called “channel” fyke net, with an increased number of hoops.
Type I fyke nets are used from spring to autumn. They can either be used individually, or if the bottom of a reservoir is suitable, arranged in patterns of two or more. The nets are set in shallow inshore and midlake areas, mostly because they must be supported by wooden poles driven into the bottom. In places used for fyke net catches, paths or corridors are cut in submerged and emergent vegetation to allow for net setting. The number of such paths, which during the fishing season should be well maintained, is generally about five times greater than the number of nets. This is due to the fact that fyke nets set in the same place for a long period become less effective, and is also one of the reasons why fishing with fyke nets has a relatively high work requirement.
The average daily catch of type I fyke nets, estimated from 100 057 fyke-net/days on 105 lakes of total area 23 100 ha, amounts to 1.53 kg. The highest average daily catch of fyke nets is noted on lakes of surface area 100–500 ha, and amounts to about 1.80 kg. On lakes of area above 500 ha it is relatively lower, reaching about 1.50 kg, and on lakes smaller than 100 ha it amounts to about 1.35 kg.
Average daily catches of fyke nets decrease successively from a maximum in March (1.94 kg) and April (1.90 kg), through 1.48 kg in June, to below 0.5 kg in September and October.
The species composition of catches with type I fyke nets based upon data from the above samples is as follows for species exceeding 20 percent of the total daily catch: pike 26.13 percent (0.40 kg); tench 20.22 percent (0.31 kg); and roach 26.68 percent (0.41 kg).
The same species dominate in catches in different size groups of lakes showing definite trends associated with lake size. The proportion of pike and tench in catches decreases along with an increase of lake area. In lakes of area up to 100 ha their daily catch amounts to 31.43 percent (0.43 kg) of pike, and 28.19 percent (0.39 kg) of tench. In lakes of 100–500 ha the respective values are 27.83 percent (0.49 kg) of pike, and 20.24 percent (0.36 kg) of tench. In lakes above 500 ha area they amount to 23.98 percent (0.36 kg) of pike, and 17.43 percent (0.26 kg) of tench daily. The opposite is observed as regards roach catches which increase in proportion with an increase of lake area from 18.03 percent (0.25 kg) daily on lakes up to 100 ha, to 31.46 percent (0.41 kg) daily on lakes above 500 ha.
Catches of the different species are also characterized by clear annual tendencies. Daily catches of pike reach their maximum in March and April, amounting in these months to over 75 percent (1.46 kg) and 55.8 percent (1.06 kg) respectively. A second slight maximum occurs in October. Tench catches increase until June and July, reaching 33.56 percent (0.50 kg) and 41.16 percent (0.36 kg) per day respectively. In the following month a decrease in tench catches is noted. Roach catches increase until May (0.73 kg daily), and then gradually decrease.
In the various size groups of lakes and over an annual cycle, the respective trends and maxima of catches are similar as regards all the above species. However, there is a clear maximum of perch catches in August, occurring on lakes above 500 ha area, and a bream maximum in May and June on lakes with an area 100–500 ha.
A clear dominance of different species is observed in fyke net catches carried out on lakes belonging to various fishery types. Tench catches and pike catches dominate on lakes belonging to Crucian carp and tench/pike types. Pike and bream dominate in pike/perch and bream types; roach and tench dominate in vendace type of lakes.
The daily fishing effort of type I fyke nets amounts to 1.2 standard units (Leopold and Dabrowski, see p. 722).
From data from 278 lakes of total area of 83 990 ha, the average fishing intensity amounts to 2.72 standard units per ha and, in relation to the total fishing intensity on these lakes, it represents 9.4 percent.
On lakes with an area up to 100 ha fishing intensity with type I fyke nets amounts to 2.73 standard units per ha, on lakes ranging from 100–500 ha to 2.94 standard units per ha, and on lakes above 500 ha to 1.94 standard units per ha.
The greatest fishing intensity with fyke nets is independent of size of lake and occurs during the period April-July when it reaches over 96 percent of total intensity; the maximum (35 percent) occurs in June.
From a sample of catches carried out on 324 lakes with total area of 91 277 ha over, on average, a four-year period, fishing with type I fyke nets is carried out on 85.8 percent of lakes by number and 92.0 percent by total area. Type I fyke net catches give, on an average, 10.9 percent of total catches obtained on those lakes.
Type I fyke nets affect the population of fish exploited to a high degree. Studies have shown that there is a very strict (p = 0.001) negative correlation between fishing intensity with type I fyke nets and their average daily catch. From analysed data, an increase (or decrease) of fishing intensity of fyke nets by one standard unit per ha is connected with an average decrease (or increase) of their average daily catch by 0.08 kg. Fishing intensity with type I fyke nets correlates also, although in a lower degree (p = 0.05), with total catch on a given lake.
From the above, and also the fact that there is little connexion between daily catch of type I fyke nets and total catch on lakes, it may be stated that this gear is not a satisfactory measure of the state of total stock in lakes. This seemingly results from the fact that the selectivity of type I fyke nets is very variable in respect of different fish species caught.
However, it may be expected that if regularities existing between catches with these nets and their effect on different species caught (especially on pike and tench) were properly determined, catches with fyke nets might become a valuable measure of the state of fish stock and its trends.
Type I fyke nets are used rather unwillingly by fishermen, as they can be used for poaching, and have considerable work requirement.
According to the studies of the Agricultural-Technical Academy, the daily labour cost of catches with type I fyke nets, expressed in calories expenditure, amounts to 51.5 kcal.
The calculated daily fishing effort amounts to 42.9 kcal per standard unit and, in relation to other fishing gear used in Poland, is the highest. When calculated per average daily catch, the labour cost of type I fyke nets amounts to 33.6 kcal/kg of fish; this being rather high in comparison with other types of fishing gear.
Fishing with type I fyke nets needs a high work requirement, 5.5 kcal/min.
Type I fyke nets are characterized by a very strict correlation between their average daily catch and fishing intensity. As a result of this correlation, they are highly satisfactory as a measure of the density of several fish species. Although no detailed studies were carried out, it was provisionally noted that catches of pike and tench strongly depend on the fishing intensity of type I fyke nets. This is also indicated indirectly by a correlation between their rather low intensity and total catch on a lake. Thus, type I fyke nets may be used as a measure of the density of pike and tench which is most effective on smaller lakes.
It is probable that an evaluation of correlation between fishing intensity of type I fyke nets and catches of pike and tench, calculated in conjunction with the correlation existing between intensity and daily catch, would allow for a reliable estimate of absolute density of these species in lakes.
Type II fyke nets usually consist of one or two traps and two non-return valves. Their construction is very similar to that of type I fyke nets, plus an additional portion stretched on a semicircular hoop which makes the gear more stable. The cord of the semicircle lies on the bottom of a reservoir and in large fyke nets it is often weighted. The heightened and widened additional part, due to its semicircular shape, increases the fishing efficiency of the gear. The height of the semicircle varies from 120–150 cm. The mesh size in the trap ranges from 30–55 mm and the length of the gear ranges from 3.0–3.5 m. The leaders are up to 7 m long. The size of special types of type II fyke nets varies depending on fish species to be caught.
Fishing with type II fyke nets is carried out from early spring to autumn. As compared to type I nets, type II nets are easier to set because they are not supported on wooden poles; and they can therefore also be set in deeper parts of lakes. Type II fyke nets can be set on any type of bottom — hard, muddy, or overgrown with vegetation — and there is no need to cut plants as the loaded cord presses them to the bottom. The nets are usually set on the slopes of the lake basin; good results are also obtained in early spring when the gear is set under the ice cover. Single nets are used for fishing in weed beds or on lakes with narrow inshore area and rapidly sloping bottoms as in these cases it is impossible to arrange patterns of nets. Double nets are used in lakes with relatively gently sloping bottoms and are usually set in patterns. Connexion points between individual fyke nets are loaded, and a continuous line of nets is formed. Such patterns of fyke nets are especially effective for pike.
The average daily catch of type II fyke nets amounts to 1.75 kg as estimated from 54 042 fyke-net/days from 44 lakes with a total surface area 15 042 ha.
The average daily catch of the nets is 1.93 kg in lakes of up to 1 000 ha, and 1.72 kg in lakes above 1 000 ha.
Maximal average daily catches of fyke nets, amounting to 2.37 kg, in lakes with an area up to 1 000 ha occurs in May while in lakes above 1 000 ha it occurs in June and amounts to 2.30 kg. In lakes of the first group (up to 1 000 ha) relatively high daily catches of fyke nets are maintained until August, while in the second group (above 1 000 ha) they already show a decline in July.
Based upon the above samples the following species are dominant: pike 44.20 percent (0.77 kg daily); bream 22.69 percent (0.40 kg); tench 15.71 percent (0.28 kg); and roach 10.88 percent (0.19 kg).
The above species maintain their leading role in both size groups of lakes. Any difference observed occur mostly in tench and bream catches which species exchange places to some extent. Thus, in lakes up to 1 000 ha tench catches amount to 22.28 percent (0.43 kg daily) while bream catches amount to 15.19 percent (0.29 kg). On the other hand, in lakes bigger than 1 000 ha tench catches amount to 14.59 percent (0.25 kg daily) while bream catches amount to 23.98 percent (0.41 kg).
Interesting variations occur annually connected with different conditions in the two groups of lakes. Thus, on lakes with an area up to 1 000 ha maximal pike catches occur in March constituting 100 percent (1.87 kg daily), and in April almost 80 percent (1.47 kg daily) of the total catch while on lakes with an area above 1 000 ha, this maximum extends also in to May. In the latter lakes the proportion of pike in fyke net catches amounts to 87.58 percent (1.53 kg daily) in March, 72.65 percent (0.97 kg) in April, and 64.82 percent (1.06 kg) in May. A second, much lower peak of pike catches is noted in autumn. In the smaller groups of lakes this occurs in September while in the larger lakes it extends in to October and November. Tench catches carried out with fyke nets are characterized by similar trends. On lakes with an area up to 1 000 ha, maximal catches are observed in June and July amounting to 40.91 percent (0.67 kg daily) and 55.62 percent (0.89 kg) respectively, while on lakes above 1 000 ha the maxima occur in June, July and August respectively amounting to: 21.82 percent (0.50 kg), 54.89 percent (0.54 kg), and 74.46 percent (0.49 kg) daily. Maximal bream catches occur in May on the smaller lakes 25.69 percent (0.61 kg daily), and in June on larger lakes 45.89 percent (1.06 kg daily).
The daily fishing effort with type II fyke nets amounts to 1.9 standard units.
The average fishing intensity based upon data from 190 lakes with total area of 57 719 ha amounts to 2.06 standard units per ha and, in relation to total fishing intensity on these lakes, it represents 7.9 percent.
There is no apparent relation between fishing intensity with these nets and the size of lake. On lakes of area up to 100 ha it amounts to 2.50 standard units per ha, on lakes 100–500 ha to 1.55 standard units per ha, and on lakes above 500 ha to 1.73 standard units per ha.
The greatest fishing intensity with type II fyke nets, reaching 90 percent of total intensity, occurs during the period April-June, with a maximum in May reaching 50 percent.
From a sample of catches carried out on 324 lakes with total area 91 277 ha over a four-year period, fishing with type II fyke nets is carried out on 58.6 percent of lakes by number, and on 63.2 percent by area. Type II fyke net catches give, on an average, 7.9 percent of total catches on those lakes.
Although type II fyke nets apparently resemble type I fyke nets, they are characterized by totally different tendencies with respect to the fish caught and studies have shown that their fishing intensity correlates neither with their average daily catch, nor with the total catch on a given lake.
A relatively weak correlation between daily catch and total catch of fish on lakes points to a possibility of using type II fyke net catches as a supplementary measure only of the state of fish stock on those lakes. In this context, catches with these nets would only verify assessments based on other, more valuable fishing gear. However, studies have shown that type II fyke nets are a good indicator of the density of large pike. This applies especially to big lakes, on which the nets are set relatively deeply, and in late autumn catch the big spawners.
In Soviet literature on the subject, type II fyke nets are regarded as an extremely efficient fishing gear, catching almost all species in littoral and sublittoral zones. However, due to the considerable work requirement for fishing with this gear, it is used unwillingly by Polish fishermen.
According to the studies of Agricultural-Technical Academy, the daily labour cost of catches with type II fyke nets, expressed in calories expenditure, amounts to 55.2 kcal.
The calculated daily fishing effort amounts to 29.0 kcal/standard unit and, in relation to other fishing gear used in Poland, remains, after trammel nets and perch/roach gillnets, the lowest. When calculated per average daily catch, the labour cost of type II fyke nets amounts to 31.5 kcal/kg of fish which, although more favourable than for the type I fyke net, remains average.
Fishing with type II fyke nets, as with all types of trap nets, has a high work requirement, about 5.5 kcal/min.
Type II fyke nets have only a limited value as a measure of the density of fish stock, even as regards the density of the species caught by this gear. In order to utilize these nets as such a measure, it is absolutely necessary to carry out additional studies.
However, the nets are a satisfactory measure of the density of big pike populations particularly in larger lakes where they spawn much later and deeper than small pike and are thus caught by this gear.
Wing nets are usually a combination of three or four hoop nets connected by wings and leaders (fences). They may be called “two-wing” nets (three traps), or “four-wing” nets (four traps), depending on the number of hoop nets they consist of. Wing nets are frequently modified in order to increase their fishing efficiency. Such modifications generally consist of introducing different details of construction such as: an increased number of hoops, elongated traps, covers, different length of wing, etc. A wing net usually consists of a big main hoop net, slightly smaller side traps, and in the case of four-wing nets, a small front trap. The size of traps is similar to those of fyke nets. Mesh size varies from 25–40 mm.
Wing nets are used during practically all periods when there is open water. Two-wing nets are employed mostly on shallow inshore areas, densely overgrown with submerged vegetation. During the spring, directly after the thaw, very good results are achieved on flood waters. The best results are obtained with nets set in places exposed to the wind, and in places with strong air currents, as for example, close to peninsulas, etc. Four-wing nets are used on deeper and larger inshore areas, the leader of the main trap being set perpendicularly to the shore; thus, the small, front trap is set in the shallowest area and the big, main trap in the deepest. Wing nets are also set on large shallow areas in the middle of the lake. Sometimes separate wing nets are set in patterns being connected to each other by fences which may even be up to several metres long. Such patterns are used particularly in places of in- or outflow from lakes. Best catches with wing nets are achieved during dark nights and windy, cloudy days. Wing nets are used almost exclusively for catching eels.
The average daily catch of wing nets amounts to 2.45 kg, as estimated from 33 746 wing- net/days from 129 lakes with a total surface area of 28 168 ha. The coefficient of variability (V%) is very high and exceeds 100 percent.
The average daily catch of wing nets is different in various size groups of lakes. The lowest value is noted on lakes with an area above 500 ha, 2.26 kg; on lakes up to 100 ha it amounts to 2.42 kg and the highest value occurs on average lakes (100–500 ha) 2.81 kg.
The highest average daily catch of wing nets occurs in March and April, 3.68 and 2.94 kg respectively per wing-net/day and to some extent also in August, 2.77 kg.
Data on the qualitative composition of catches are based upon materials from 140 lakes with a total surface area of 31 554 ha.
Eel is definitely the predominant species in wing-net catches. On average it comprises 50.1 percent (1.23 kg) of the daily catch. Pike and roach also represent a significant portion, i.e., 13.0 percent (0.33 kg) daily each.
Eel predominates also in wing-net catches in each size group of lakes. In lakes with an area up to 100 ha its share in daily catches reaches respectively 41.5 percent (1.0 kg), in lakes 100–500 ha 61.1 percent (1.71 kg), and in lakes bigger than 500 ha 46.0 percent (1.04 kg). In the last group a significant proportion of bream catches is also noted, amounting to 18.2 percent (0.41 kg).
Two maxima are distinguished during the year for eel catches carried out with wing nets in spring; April 48.2 percent (1.42 kg) and May 62.6 percent (1.30 kg) daily, and in autumn; August and September over 50 percent (1.0 kg) daily each month. Similar tendencies are observed with regard to catches of pike and roach. In the case of pike, however, there is a certain displacement of the spring maximum to March; the proportion of pike catches in March reaches 31.9 percent (1.17 kg) daily. Apart from the above discussed species, all other species reach their maximum in June, mostly as a result of high tench catches.
The above tendencies are similar for each size group of lakes except that on lakes with an area up to 100 ha a maximum catch of tench (30 percent) is observed in June.
Daily fishing effort of a wing net amounts to 2.7 standard units.
Based upon data from 181 lakes with total area of 63 280 ha, the mean (weighted) fishing intensity amounts to 1.59 standard units per ha. The arithmetic mean amounts to 1.16 standard units per ha and, in relation to total fishing intensity on these lakes, this value represents 4 percent.
On larger lakes the intensity of fishing with wing nets is relatively higher; on lakes ranging from 0–100 ha it amounts to 0.82 standard units per ha, on lakes 100–500 ha to 1.17 standard units per ha and on lakes with an area above 500 ha 1.83 standard units per ha.
The highest rate of fishing intensity with wing nets, reaching 90 percent of the total, occurs in the period April-June and the maximum (45 percent) occurs in May for all size groups of lakes.
From a sample of catches carried out on 324 lakes with total area of 91 277 ha over a four-year period, fishing with wing nets is carried out on 55.9 percent of lakes by number, and on 69.3 percent by total area. Wing-net catches give, on average, 3.6 percent of total catches obtained on those lakes.
Wing nets belong to those fishing methods clearly affecting the population of fish caught by them. Studies have shown that there is a strict (p = 0.01) negative correlation between the fishing intensity of wing net and its daily catch. An increase (or decrease) of wing-net fishing intensity by one standard unit per ha is associated with a decrease (or increase) of its daily catch by 0.47 kg.
The fishing intensity with wing nets clearly determines the level of eel catches. Studies on the efficiency of wing nets have shown that on those lakes on which wing nets are not used, eel catches are 45 percent lower. An increase (or decrease) of wing-net fishing intensity by one standard unit per ha produces an average increase (or decrease) of eel catches by 0.4 kg/ha.
Independently of the strongly pronounced selectivity of wing nets for eel, their daily catch may be considered at least as a complementary measure of the density of a whole fish stock in a given lake as there is a positive correlation (p = 0.05) between daily catch of wing nets and total catch (in kg/ha) on a given lake.
Wing nets should be regarded as an exceptionally efficient fishing gear. Reviewing lake management in Poland, there are several cases known where wing-net catches have given up to 47 percent of the total catch on a 1 000 ha lake, while the proportion of wing-net fishing intensity to the total fishing intensity amounted to 40 percent. Broad possibilities of applying wing nets for catches of other species apart from eel should also be underlined.
According to the studies of Agricultural-Technical Academy, the daily labour cost of catches with wing nets, expressed in calories expenditure, amounts to 110 kcal.
Calculated per daily fishing effort, it amounts to 40.6 kcal per standard unit and, after type I fyke nets, is the highest. Calculated per average daily catch, however, it becomes the highest, amounting to 44.8 kcal/kg of fish.
Fishing with wing nets, as with all types of trap nets, have a relatively high work requirement, about 5.5 kcal/min.
Wing nets constitute a highly satisfactory measure of the density of eel stocks, not only as regards relative estimation of the density, but also in respect to an absolute evaluation. The latter possibility results from a positive correlation existing between fishing intensity of wing nets and their daily catch on one hand, and between fishing intensity with wing nets and eel catches, on the other.
To a limited degree, wing nets may also constitute a measure of the density of all fish in a given lake - and especially of those species toward which they act selectively.
The high work requirements of fishing with wing nets limit their exclusive use as a measure of the state of fish stock.
It is not possible to give detailed characteristics as concern size of trap, length of wings and leaders, mesh size, etc., for combined pound nets. The nets are highly differentiated, consisting of a different number of traps, wings, leaders, fences, etc. Fyke nets, wing nets or a trap opening at the top may be used as the main element of a combined pound net. The varying construction and use of this fishing gear results from the fact that it is adapted to conditions in a given lake and to the behaviour of different fish species.
Combined pound nets are used on systems of lakes being set between two basins and especially in narrow parts of lake basins, outflows and inflows. They are usually set across fish migration paths. Combined pound nets are used from spring to autumn, very often being set permanently for a whole fishing season. In spring they are used to catch fish during their feeding, spawning, and post-spawning migrations, and in autumn during their wintering migrations. At in- and outflows combined pound nets are used mostly to catch silver eel, during the downstream migration.
The average daily catch of combined pound nets amounts to 46.14 kg, as estimated from 138 lakes with total surface area 44 754 ha. In view of the above discussed tactics of fishing, this value is hardly representative. Variability of catches with combined pound nets is extremely high, depending on their application in different lakes, or on the same lake but in different years and periods as also on the details of construction. In particular lakes the catch can vary from a statistical zero to 400 kg per day.
Highest average daily catch with combined pound nets is observed on lakes of area 100–500 ha, where it reaches 51.49 kg; on lakes up to 100 ha and above 500 ha it is lower and reaches 38.16 and 40.23 kg respectively.
In an annual cycle the highest catch with combined pound nets occurs most frequently in spring, with a maximum in May. Sometimes exceptionally high catches are noted in autumn with a maximum in September. Detailed studies on this gear have not been completed.
Data on the qualitative composition of catches are based on relatively restricted materials from two complexes of lakes, consisting of seven lakes with a combined area of about 20 000 ha.
Species dominating in the catches of combined pound nets are: roach 37.3 percent; bream 18.4 percent; eel 17.2 percent; and perch 10.6 percent of average daily catches.
Daily catches of combined pound nets for different species during the year are as follows:
roach: 85.4 percent in March; 58.8 percent in April; 41.5 percent in May; and 43.6 percent in December
bream: 30.6 percent in June; and 23.4 percent in May
eel: 27.9 percent in September; 23.5 percent in October; 14.5 percent in May
perch: 27.3 percent in September.
It is worth underlining that the role of these maxima in total catches (in an annual cycle) of a given species is sometimes very important; and thus, in May almost 50 percent of roach is caught; almost 60 percent of bream; and almost 40 percent of eel; in September almost 60 percent of perch is caught.
The daily fishing effort of a combined pound net amounts to 28.5 standard units.
The average fishing intensity calculated from data from 144 lakes with total area of 49 804 ha, amounts to 1.33 standard units per ha, constituting 4.5 percent of total fishing intensity on these lakes.
Fishing intensity with combined pound nets decreases along with an increase of lake areas. On lakes with an area up to 100 ha it amounts to 1.60 standard units per ha, on lakes 100–500 ha to 1.43 standard units per ha, and on lakes above 500 ha to 0.50 standard units per ha.
Although detailed data are not available, it may be stated that the highest rate of fishing intensity with this gear takes place in spring, from April-June (65.6 percent of total intensity). A maximum is noted in May (31.2 percent) and a second, lower maximum (only 10 percent) of the rate of fishing intensity occurs in autumn, in September.
As from a sample of catches carried out on 324 lakes with total area of 91 277 ha over a four-year period, the combined pound net is used on 44.4 percent of lakes in respect to their number, and on 54.6 percent in respect to the area. Its catches amount to 5.5 percent (on average) of total catch on these lakes.
Studies have shown that there is no statistically significant correlation between either the fishing intensity of this gear and its average daily catch, or its daily catch and total catch in a given lake. This is probably due to the flexible construction of the gear and the resulting strongly pronounced variability of catches.
Nevertheless, there is a statistically significant (p = 0.01) positive correlation between fishing intensity of catches with combined pound nets on given lakes and total catch of fish on these lakes. Thus, the combined pound net is a gear with a high productional efficiency, influencing total catch obtained on a given lake despite its low fishing intensity. Thus this gear may, in some cases, be used as a measure of the state of fish stock, but only with considerable restrictions.
The labour cost of fishing with combined pound nets was not studied but it may be assumed to be as diverse as its construction and methods of catches.
Independently of the significant limitations in applying combined pound nets as a measure of the state of fish stock, the gear is highly valuable in this respect. Due to specific fishing tactics and the period during which it is used, the combined pound net may become a source of valuable information on fish migrations in a reservoir and may provide considerable data on these fish. Catches with combined pound nets carried out during spawning period of roach and bream, provide especially valuable materials on the structure of spawning stock, frequently allowing for reliable forecasting of future catches.
According to direct information received in fish farms, it appears that the gear is becoming less and less used due to the considerable work requirements and difficult method of fishing.
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