DISTRIBUTION OF PIKEPERCH, SANDER LUCIOPERCA (L.), HABITATS IN RIVER DRAINAGE BASINS IN NORTHEASTERN POLAND IN 1951-1994

Andrzej Skrzypczak, Andrzej Mamcarz
Department of Lake and River Fisheries, University of Warmia and Mazury in Olsztyn, Poland

ABSTRACT

The study was completed on the basis of the results of commercial fish catches from lakes in Northeastern Poland. The number and status of the pikeperch lake habitats were determined in 14 river basins in this part of Poland, as recorded in 1951-1994. The river basins differed in the potential of the lakes inhabited by this predatory fish. The highest percentage of such lakes relative to all lakes larger than 10 ha was found in the river basins of the Liwa, Pasłęka and Osa. The status and distribution of pikeperch habitats were established at the beginning and in the final years of the time period analyzed. The total increase in the number of lakes settled by pikeperch was 209, with the aggregate area of pikeperch habitats rising by 41 365 ha. The dispersion of pikeperch was not connected directly with the fish stocking carried out during that time. In the Ełk and Pisa river basins, over 90% of new pikeperch habitats appeared owing to natural migration of this fish species.

Key words: pikeperch (Sander lucioperca), distribution, habitat, lakes, river basins, Northeastern Poland.

INTRODUCTION

Pikeperch, Sander lucioperca (L.), as a biologically and commercially valuable component of lake ichtiofauna [17], has been an object of many studies and publications at the turn of the19th and 20th centuries and in the interwar years [26]. Due to the small numbers of this fish species living in the lakes of Northeastern Poland in the 1930s and 1940s [1, 11], intensive stocking with pikeperch was undertaken in the early years of establishing fishery management in Poland [23].

The distribution of pikeperch populations has been recognized more thoroughly owing to some research on the exploited populations of pikeperch [3, 19]. This predatory fish is often used as an indicatory species for early eutrophication of lakes [2]. Based on the results of commercial fish catches in lakes, analyses of pikeperch dispersion in the Great Masurian Lakes have been made [22]. In addition, the occurrence of this predator in various classes of habitats in Northeastern Poland has been specified, characterization of the habitats [24].

The objective of this paper is to analyze spatial and time-related differences in pikeperch distribution recorded in 1951-1994 in the river basins of Northeastern Poland.

MATERIALS AND METHODS

Northeastern Poland is a region characterized by the largest total area of lakes in the country. Its borderlines are delineated by the Lower Vistula River to the west, the last Baltic glaciation to the south and state borders to the east and north [12].

The area of Northeastern Poland is highly diverse and its water resources are not distributed evenly. Therefore, for the purposes of this study, the area has been divided into 14 river basins (Fig. 1). The division was based on the natural pattern of the water network in this part of Poland [6, 8], and the boundaries of each basin are delineated by the watersheds of the river basins. The name of each the river basin is the name of its main watercourse.

The Czarna Hańcza river basin covers the part of the Niemen river basin lying on the Polish side. The main watercourses, which together with the lakes and tributaries, create the area’s water network are the Czarna Hańcza, Szeszupa, Biała Hańcza and Marycha rivers.

All of the Drwęca river basin (a right tributary of the Vistula river) lies in the area covered by our investigations. The main tributaries of the Drwęca which contain lake catchments are the Wel, Brynica, Skarlanka, Rypienica, Ruziec, Lubianka and Struga Rychnowska.

The Elblšg river basin belongs to the Vistula Lagoon direct basin and makes up an area whose waters are drained by the Dzierzgoń and Wšska rivers. These two watercourses fall into Drużno Lake. The Elblšg river flows out of Drużno Lake and falls into the Vistula Lagoon. The western boundary of this area is demarcated by the Nogat river.

The Ełk river basin covers an area whose waters are drained into the Biebrza river (the Narew-Vistula basin). The primary watercourses which, together with their tributaries, constitute the water network in this territory are the rivers Ełk, Rospuda-Netta, Szczeberka, Jerzgnia and Lega.

The Fryba river basin encompasses an area from which waters are drained directly to the Vistula by the Fryba river as well as the Struga Toruńska, Struga Łysomicka and many other small, nameless streams, some of which originate in one of the lakes lying in this corner of Northeastern Poland.

The Liwa river basin belongs to the Vistula Lagoon basin. The Liwa carries its waters to the Nogat river, and its main tributaries are the Miłosna and the Podstolińska Struga. This river basin has another connection with the Nogat via the Jurand Canal, which reaches Dšbrówka Lake.

The Łyna river basin covers a large area, which makes up the Polish part of the Pregoła river basin (the Vistula Lagoon basin). The complex water system in this area consists of the main river with its many tributaries: the Guber, Pisa, Wadšg, Marózka, Kortówka, Dajna, Sajna and Œwinia rivers.

The Mień river basin comprises the river Mień (a right tributary of the Vistula) basin together with a small area below the river’s mouth. It is drained directly to the Vistula by the Mień and Młynówka rivers as well as two nameless streams.

The Omulew river basin belongs to the Narew river (a right Vistula river’s tributary) basin and is drained by the upper courses of the rivers (to the southern limits of the Baltic glaciation) which are right tributaries of the Omulew: the Omulew and its tributaries, the Orzyc, Rozoga, Szkwa, Nida and Szkotówka rivers (the latter two are the tributaries of the Wkra river).

The Osa river basin (a right tributary of the Vistula) is an area drained by the Osa and all its tributaries, of which the Lutryna and Gardęga are the largest.

The Pasłęka river basin covers an area which belongs to the Vistula Lagoon basin. It is composed of the basin of the Pasłęka and its tributaries (the Drwęca Warmińska, Gilwa, Moršg, Młyńska Struga, Miłakówka and Wałsza), the lakeless basin of the Bauda river (flowing to the Vistula Lagoon), the Polish part of the Banówka river basin (flowing to the river Jarft) and the Polish part of the Œwieża (Prochladnaja) river basin – the Stradyk.

The Pisa river basin covers the catchment of the southern part of the Great Masurian Lakes together with the basins of the rivers which flow into this geographical area of the Great Lakes. The principal rivers are the Krutynia and Orzysza. The Pisa, which flows out of Roœ Lake, carries the waters from this basin into the Narew river (a tributary of the Vistula). The northern boundary of this area lies at the watershed crossing the Great Masurian Lakes. The watershed is movable and, according to Mikulski [16], is most often located in the northern part of Niegocin Lake, which has been classified as belonging to the Pisa river basin.

The Skrwa river basin is the southernmost area covered by the present study. It encompasses the Skrwa river basin (a right tributary of the Vistula) and a small area below the mouth of the Skrwa river. It is drained by some nameless streams, which carry water from the local lakes directly to the Vistula.

The Węgorapa river basin is another (after the Łyna river basin) part of the Polish section of the Pregoła river basin. It covers the catchment of the northern part of the Great Masurian Lakes, together with the Sapina river basin, the Polish part of the Węgorapa river basin and all upper sections of the basins of the rivers flowing outside Poland’s state borders (the Rominta and the Pissa).

None of these river basins is a closed system. There are many the so-called water gates at the watersheds, which indicate the sites of bifurcation of natural watercourses and manmade canals or draining sitches [7].

A general description of the water resources in the analyzed river basins is presented in Table 1. The total number of water bodies of an area over 10 ha in the territory covered by the present research project is 1003, and their aggregated surface area is 132.45 thousand ha.

Based on the records in the management books for the lakes of Northeastern Poland, made in 1951-1994, the authors selected a group of reservoirs in which pikeperch occurred in fishing statistics. The lake books provided information on pikeperch stocking. The lakes were assigned an appropriate category as pikeperch habitats according to the frequency of occurrence of this fish species in commercial catches. This index was expressed as a ratio between the number of years when pikeperch was present in catches to the total number of the years when exploitation was carried out. The index served to divide the lakes into three categories of pikeperch habitats: A (≥0.75) – considered as permanent in character, B (0.74-0.25) – considered as temporary and C (<0.25) – considered as incidental.

The area of the lakes for computations was taken from the IRΠdatabase after [4].

The spatial analysis system MapInfo (version 4.5) was applied for the graphic interpretation of the results.

RESULTS

The presence of pikeperch habitats, in which this fish species stayed for different lengths of time between the years 1951 and 1994, was confirmed in all the analyzed river basins in Northeastern Poland. The detailed data on the number and area of habitats, divided into several categories, are comprised in Table 2. The biggest numbers of permanent habitats (category A), of which the total of 116 were distinguished (46 246 ha), were found in the basins of the Łyna (21), Pisa (20), Drwęca (19) and Ełk (18). These four river basins were also characterized by the highest numbers of temporary (category B – the total of 138 out of 215 registered lakes) and sporadic pikeperch habitats (category C – the total of 172 out of 288 registered lakes). The highest total surface area of lakes in which pikeperch was observed was determined in the Pisa river basin: 34 069 ha (including 9975 ha of Lake Œniardwy excluding its bays). No permanent pikeperch habitats were found in the river basins of the Czarna Hańcza and the Fryba; the Elblšg river basin had no sporadic pikeperch habitats.

The river basins in Northeastern Poland varied in the numbers of pikeperch habitats and in their percent contribution to the total number of lakes (>10 ha) located within these basins (Fig. 2). In 1951-1994, the highest number of pikeperch habitats was recorded in the Drwęca (121 lakes covering 16 165 ha) and the Łyna (104 lakes of the surface area 15 410 ha) river basins. The water reservoirs inhabited by pikeperch in the eleven river basins (see Fig. 2) made up over 50% of all the lakes larger than 10 ha. The highest value of this parameter was recorded for the river basins of the Liwa (90.5%) Pasłęka (85.7%) and Osa (84.4%). The smallest percentage of pikeperch habitats accounted in the river basins of the Czarna Hańcza (24.7%), Fryba (29.6%) and Elblšg (33.3%).

For the map of zoogeographic distribution of pikeperch in Northeastern Poland, recorded in 1951-1994, the most important were habitats in which the fish stayed for the longest periods, that is the permanent (category A) and temporary ones (category B). In the majority of the river basins (8), the percentage of permanent and temporary habitats in the total number of lakes larger than 10 ha varied within the range of 32.5% for the Ełk river basin to 38.1% for the Liwa river basin (Fig. 3). The highest percentage of category A and B habitats was recorded in the basins of the rivers Pasłęka (60.0%), Skrwa (41.7%), Drwęca (40.6%) and Mień (40.0%). The smallest contribution of such habitats to the total number of lakes was seen in the basins of the rivers Czarna Hańcza (5.2%) and Fryba (11.1%).

From the fishery management logbooks on commercial catches of fish in the lakes of Northeastern Poland dating back to the early 1950s, it was possible to determine the initial numbers of the pikeperch habitats in each category. The presence of pikeperch at that time was confirmed in the total of 142 water bodies (47 290 ha) lying in the twelve river basins analyzed (Table 3). Permanent habitats (category A) prevailed and were the most numerous in the river basins of the Pisa (16 lakes), Łyna (15 lakes), Ełk (15 lakes) and Drwęca (11 lakes). Pikeperch was absent in the river basins of the Skrwa and Fryba. In the Czarna Hańcza and Liwa river basins it occurred in single lakes, in the habitats classified as sporadic (category C).

In the early 1950s the highest total numbers of pikeperch habitats were found in the Drwęca and Ełk river basins – 27 lakes in each of the basins (Fig. 4). In 8 out of 14 examined river basins these lakes constituted over 20% of the pikeperch habitats in which this species occurred until 1994. The highest value of this parameter was determined in the Omulew (40.1%) and the Ełk (34.2%) river basins.

In the final four years of the time period investigated, pikeperch was present in Northeastern Poland in 351 lakes covering the total area of 88 655 ha (Table 4). Over 47% of these habitats belonged to category B (166 water reservoirs of a total area 35651 ha), and they appeared in the highest numbers in the Drwęca (39) and the Łyna (30) river basins. The highest number of lakes belonged to category A found in the Łyna (21) and Drwęca (19) river basins. The habitats of category A were not observed in the river basins of the Czarna Hańcza and the Fryba.

In the early 1990s, pikeperch habitats covered from 12.5% (the Czarna Hańcza river basin) to 87.5% (the Fryba river basin) of all the habitats in which it had been observed in 1951-1994 (Fig. 5). In twelve river basins the percentage of such lakes exceeded 50%, and in six it reached over 60%. The highest overall number of pikeperch habitats was then found in the Drwęca (71) and Łyna (65) river basins.

In the years 1951-1994 no correlation between the first catch and direct stocking was determined for 356 lakes (Table 5). Lack of such correlation was mainly evident for category C habitats (223 lakes of a total area of 22243 ha). The highest number of such lakes lay in the Łyna river basin (43). In all the lakes belonging to categories A and B, the occurrence of pikeperch that was not correlated with stocking was observed most frequently in the basins of the rivers Drwęca (29) and the Pisa (26).

During the years 1951 to 1994, over 50% of new habitats in 13 river basins of Northeastern Poland were settled by pikeperch owing to natural migration (Fig. 6). In 6 river basins this phenomenon appeared at a level of ≥80, and in the Ełk and the Pisa river basins, the percentage of such lakes exceeded 90.

DISCUSSION

The results seem to indicate that there are differences in the total number of pikeperch habitats observed in the river basins of Northeastern Poland. These variations, however, were only to a small extent connected with the differences in the water resources available in all the river basins. The analysis of the percentage contribution of pikeperch habitats to the total number of lakes in each river basin shows that the largest disproportions, in the permanent and temporary habitats, were seen between the Czarna Hańcza (5.2%) and the Fryba (11.1%) river basins versus the Pasłęka river basin (60.0%).

The specific environmental requirements of pikeperch and the most essential characteristics of this fish’s habitats are well known: low water transparency, not a very big average depth and no thermal stratification in summertime [14, 15, 19]. The varied number of the pikeperch habitats recorded in the river basins should be therefore associated, among other factors, with the morphometric properties of the lakes located in these river basins and the quality of their water.

The analysis of the characteristics of the three pikeperch habitat categories shows some statistically highly significant preferences of this fish species for lakes of a lower relative depth [24]. The morphological characteristics of the lakes settled by pikeperch in the Czarna Hańcza river had the highest values of the relative depth among all the river basins analyzed [21]. The fact that the water bodies located in the latter river basin were the deepest is also made evident by the ratio of the lakes to their water retaining capacity as well as the large volume of the water masses, which is confirmed by the review made by Różycki [20].

Srokowski [25], who described the water resources of East Prussia, mentioned larger natural turbidity of the lakes lying in the western part of the region, including the ones located in the upper parts of the Drwęca and Pasłęka river basins. This could have favored denser concentration of pikeperch habitats in this part of Northeastern Poland.

The general picture of pikeperch habitats in Northeastern Poland obtained in the 1950s is consistent with the data published on this issue [24, 27]. The differences in the distribution of this fish species observed ca fifty years ago dated back to the interwar years and had their roots in some political and economic conditions [23].

From 1951 to 1994 pikeperch appeared in many new habitats and inhabited them for different time lengths [24]. By comparing the state of pikeperch habitats in the early and the final years of this time period, it is possible to notice that the highest increase in the number of habitats concerned those classified as category B. The potential of these lakes rose by 124 water bodies, and the total surface area was 27 999 ha larger. The highest increase in the category A and category B lakes took place in the river basins of the Drwęca (28), Łyna (32) and Pisa (25).

There have been reports suggesting that pikeperch had settled habitats which did not adhere to the standard conditions set for pikeperch lakes [29]. Among the primary reasons for this event the researchers have indicated increasing eutrophication of lakes [5, 13], stocking [14, 17] and the fish’s occasional tendency for migration and settling in whole river systems [18, 28]. Studies on the changes in the presence of this predatory fish in lakes of Northeastern Poland suggest that while all these three factors come into play, natural migration may have a very important role in establishing new habitats of pikeperch [22, 24]. Other possible reasons explaining the differences in the distribution of pikeperch habitats between the river basins could be the extent and scale of pikeperch stocking management, the number of lakes in each river basin and the water network development.

The lakes lying in the Ełk and Pisa river basins were characterized by the lowest percentage of the lakes stocked with pikeperch and the lowest parameters defining the amounts of stocking material [23]. In these lakes, too, the incidence of new habitats appearing in the unstocked lakes was the most frequent. In these two areas, the high parameters defining lake densities coincided with the largest initial potential of permanent and temporary pikeperch habitats. Thus, it can be assumed that the occurrence of pikeperch in new habitats in the Ełk and Pisa river basins was an effect of migrations, which could have been initiated by some populations already inhabiting some reservoirs in the given area and induced to undertake migration by a change in the environmental conditions (e.g. eutrophication).

In the Czarna Hańcza river basin, the stockings with small amounts of pikeperch stocking material were carried out between 1951 and 1994 in just 14.4% of the basin’s lakes [23]. The lack of permanent habitats of this fish together with the fact that these lakes are relatively deep and unpolluted would suggest that any occurrence of this fish species that was not directly connected with pikeperch stocking in 56.5% of the lakes was more possibly associated with some migration of the stocking material that took place after its introduction.

In the Pasłęka river basin, between 1951 and 1994, pikeperch stayed, albeit for various time lengths, in over 85% of the lakes measuring over 10 ha. The results of some previous studies seem to indicate that the Pasłęka river basin was an area of the most intensive pikeperch stocking management (over 65% of the lakes were stocked) using the largest amounts of stocking material [23]. Together with the potentially favorable environmental conditions, this meant that natural migrations of pikeperch stocking material were not frequent; they were observed in 54.2% of the lakes.

The many variables that can potentially affect time- and space-related changes in the distribution of pikeperch habitats in Northeastern Poland should encourage researchers to undertake more detailed investigations. The authors realize that it will not possible to obtain many, more precise answers unless the changes occurring within each river basin are analyzed.

CONCLUSIONS

1. In the total number of lakes >10 ha, the highest percentages of permanent and temporary pikeperch habitats were determined in the river basins of the Pasłęka, Skrwa, Drwęca and Mień.

2. The highest absolute increase in the number of lakes inhabited by pikeperch between 1951 and 1991 was noticed in those river basins which had a large initial number of pikeperch potential habitats and a well developed water network.

3. The varied numbers of pikeperch habitats in the river basins under study did not reflect the total water resources available in each basin. Rather, it is a reflection of the differences in the morphological characteristics of the lakes lying in these basins, their environmental quality and the range of stocking management.

4. The scale of pikeperch migrations between water bodies in the river basins containing lakes points to an important role of a water network in the natural dispersion of this fish species.

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