Fish stock assessment in dam reservoirs located in the upper Vistula and Warta river catchment areas based on angling catch records
The regional departments of the Polish Anglers' Association (PAA) in the provinces of Bielsko-Biała, Częstochowa, and Katowice (with a combined membership of 62,163 in 2005) stipulated that anglers keep records of catches in registers. On average, 35,682 registers were analyzed annually from 2001 to 2005, which represents 57.4% of total PAA membership. The mean annual number of the anglers recording catches in dam reservoirs was 23,231, and the average catch in this category of waters was 185 tons of fish. Of the 22 fish species recorded in the catches, six comprised 91.6% of the total catch, as follows: common carp, Cyprinus carpio (L.); bream, Abramis brama (L.); roach, Rutilus rutilus (L.); pike, Esox lucius L.; pikeperch, Sander lucioperca (L.); perch, Perca fluviatilis (L.). The share of cyprinids decreased from 73.5% in 2001 to 64.8% in 2005, whereas the share of predators increased from 18.1 to 26%, in the same time period. Carp, pike, and pikeperch were the main species in the PAA stocking programs, hence the changes observed in the species composition of the catches resulted primarily from stocking. In 2005, the maximal shares of the fish species noted were as follows: carp - 64.7% (Chechło Dam Reservoir near Chrzanów), pike - 19.8% (Dziećkowice Dam Reservoir), pikeperch - 27.8% (Tresna Dam Reservoir), bream - 72.8% (Rybnik Dam Reservoir). The results indicate that eutrophication and stocking are the main factors that determine the status of fish stocks in dam reservoirs located in the upper Vistula and Warta catchment areas.
Economic ranking of the importance of fish species to lake fisheries stocking management in Poland
This paper analyzes commercial fish stocking and catches in lakes in the 2001-2007 period. The eleven fish species that are stocked most intensely were analyzed. Rank scaling was used to compare the parameter values of the analyzed fish species. This permitted ranking all of the species from the most to the least important to lake fisheries management. Pike, Esox lucius L.; eel, Anguilla anguilla (L.); vendace, Coregonus albula (L.); and carp, Cyprinus carpio L were the highest ranked species. These were followed by tench, Tinca tinca (L.), and pikeperch, Sander lucioperca (L.), as well as whitefish, Coregonus lavaretus (L.), and common Crucian carp, Carassius carassius (L.), and Prussian carp, Carassius gibelio (Bloch). The following were of marginal significance: bighead carp, Aristichthys nobilis Rich.; silver carp, Hypophthalmichthys molitrix (Val.), wels catfish, Silurus glanis (L.), and grass carp, Ctenopharyngodon idella Val.
Changes in the trophic state of Lake Niegocin based on physical, chemical, biological, and commercial fisheries data
Changes in the trophic state of Lake Niegocin were characterized based on physical, chemical, and commercial fisheries data. Analysis of nitrogen and phosphorus influx data has shown that the trophic state of the lake can be described as polytrophic for the time period of interest. A significant reduction in the influx of biogenic substances occurred following the construction of a mechanical-biological wastewater treatment plant employing chemical phosphorus precipitation technology. Shortly after the treatment plant went on line, a reduction in the amount of phosphorus and nitrogen was recorded along with an increase in lake water transparency. The changes in physical and chemical parameters presented herein correspond in general with changes in commercial fish catches. Special attention is paid to pikeperch whose yield had increased along with increasing trophic states but then declined once the treatment plant went on line. The paper emphasizes the fact that this species is one of the best indicators of eutrophication in vendace-type lakes.
Long-term changes in commercial fish catches in Lake Mamry Północne (northeastern Poland) on the background of physical, chemical, and biological data
Lake Mamry Północne, a part of the Great Masurian Lake System in northeastern Poland, is a valuable body of water from environmental, recreational, and economic points of view. The paper evaluates long-term physical, chemical, and biological parameters as well as commercial fisheries data. Nitrogen and phosphorus influx data as well as physical and chemical data indicate that the trophic state of Lake Mamry Północne can be described as moderate from 1967 to 2006, making the lake borderline β-mesotrophic and eutrophic. The lake's trophic state increased with time, manifesting itself in an increasing concentration of biogenic substances, decreasing water transparency, and worsening oxygen conditions in the hypolimnion. Changes in physical, chemical, and biological parameters generally corresponded with changes in the commercial fish catches of selected species and groups of species indicative of the process of eutrophication.
Assessing angling catches in dam reservoirs on the example of Zegrze Dam Reservoir
Three methods were used to estimate the size and structure of angling catches in Zegrze Dam Reservoir in the 1999-2001 period. The material analyzed comprised data collected from direct monitoring (798 times), 153 questionnaires, and 687 reports. The catch structure according to the questionnaires and direct monitoring was similar. Recreational anglers who completed the questionnaires reported catches of 14 fish species; three of these (bream, Abramis brama (L.), roach, Rutilus rutilus (L.), and white bream, Abramis bjoerkna (L.)), comprised 51.6% of the total catch weight. The share of predatory fish comprising pike, Esox lucius L., pikeperch, Stizostedion lucioperca (L.), and wels, Silurus glanis L., was 31.1% of the total catch weight. The anglers who were monitored directly caught 12 species of fish, and bream dominated the catch weight at 55.0%. The share of predatory species was 33.4%. The anglers using the fishing camps demonstrated the greatest interest in predatory species, which comprised a total of 35.4% of the overall biomass of their catch. The estimated size of the catch according to questionnaires was 42842 kg or 13.0 kg ha-1, while the fishing intensity was 0.20 kg fisher-1 hour.-1. According to direct monitoring, the size of the annual catch was 33544 kg, which corresponds to an effectiveness of 10.2 kg ha-1. The results indicate that the questionnaire and direct monitoring methods are compatible, and that it is generally necessary to choose uniform study methods. When using the questionnaire method, it is essential to verify the results obtained through direct monitoring at the fishing grounds. The method of catch reporting by the fishers using the fishing camp is only of auxiliary significance.
The results of a questionnaire survey of the managers of fisheries enterprises entitled to operate in fisheries zones are presented. The aim of the study was to determine the degree to which selected factors have a negative impact on the functioning and development of fisheries. The impediment posed by the different factors was determined with a rating scale. The factors that posed impediments were ranked, from greatest to smallest, as follows: cormorant predation on ichthyofauna; commercial and recreational fisheries poaching; national and local administrations (e.g., flawed laws, bureaucracy, incompetence, etc.); unenforced regulations and laws or the lack of them; excessive leasing fees; water eutrophication and pollution; development of recreation linked with the aquatic environment; eco-terrorism, other fees payable to the state in addition to leasing fees; difficulties with selling fish; recreational fisheries pressure.
The aim of this paper is to present and discuss the results of a survey of fishers exploiting dam reservoirs to determine the conditions of conducting fisheries associated primarily with climate change. Overall, questionnaires were obtained from 18 enterprises (of which 16 were chapters of the Polish Anglers Association) regarding a total of 30 reservoirs with a combined surface area of 29,666 ha, which is 49% of the total surface are of this type of basin in Poland, the largest country in East-Central Europe. This sample is highly representative of all the fisheries conducted in this basin category in Poland and in other East-Central European regions. The following questions referring to the impact of climate change were defined and analyzed based on the answers obtained from the questionnaires: survival of hatchlings, fry, and adult fish; the spawning success of selected fish species; selected hydrological and biological reservoir parameters, the possibility of using and the effectiveness of fishing gears; the length of the recreational fishing season; the size of recreational and commercial fisheries catches of different fish species. Information regarding the impact of reservoirs on fish migrations was also obtained.
Sixty officers of the fisheries guard from three regions in northeast Poland, an area that is rich in inland waters, were surveyed. The results obtained are presented as percentages of each possible answer to each question and as rankings on a five-point scale. Those surveyed reported that the most common motivation for serving in the guard was an interest in nature, followed by an interest in recreational fisheries and then their own material and living conditions. Those surveyed reported that the principal motivation for poaching was to earn profits and as a consequence of unemployment. Sixty percent of officers reported encountering aggression from those who were monitored. Ninety percent of officers reported receiving threats from those monitored. The officers surveyed ranked their professional experience the highest among factors that impacted the effectiveness of the activities performed by the fisheries guard and the possibility of safeguarding ichthyofauna against poaching.
Poaching is still a great problem in Poland. Officers of the fisheries guard from three regions in northeast Poland rich in natural inland waters were surveyed. The most frequent type of poaching encountered by the officers was that practised by recreational fishers using rods (ranking of 4.4 points on a scale of 0–5) followed by poaching stemming from poverty or unemployment (3.4 points), and poaching by professional fishermen was ranked the lowest (1.5 points). Organized poaching was identified as the most dangerous for ichthyofauna (42% of responses), followed by poaching by recreational fishers (28%) and poaching stemming from poverty or unemployment (23%). According to the officers surveyed, the species that were targeted by poachers most frequently were the predators: pike, Esox lucius (98% of responses), European eel, Anguilla anguilla, pikeperch, Sander lucioperca and perch, Perca fluviatilis.