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    Wyświetlanie 1-7 z 7
    Tytuł:
    Seasonal differences in situ measurements of the target strength of vendace (Coregonus albula L.) in lake Pluszne
    Autorzy:
    Świerzowski, A.
    Doroszczyk, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332127.pdf
    Data publikacji:
    2004
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    The subject of the study was vendace Coregonus albula L. This species is a typical planktivore and inhabits the pelagic zone of Lake Pluszne (area - 903 ha, 51 m - maximum depth) located in northeastern Poland. Acoustic measurements were taken with a Simrad EY-500 type split beam echosounder at a frequency of 120 kHz, with beam divergence of 7x7 degrees and a pulse duration of 0.3 ms. The data were analyzed using the trace tracking method with the EP 500 program and 5696 fish traces. A total of 3092 vendace individuals were caught in various water layers with a pelagic trawl during control fishing. The study involved determining the dependence between the acoustic size of vendace TS in dB, body length L in cm and specimen weight. The measurements were carried out in June and October 2003 under varied environmental conditions that limited spatial distribution, density and the condition of the examined fish. The dependencies of TS (dB) on fish body length L (cm) were determined for the average values of TSS.A. = 20 log L –65.4 š 0.1 SE and TSmax = 20 log L –63.8 š 0.1 SE.
    Źródło:
    Hydroacoustics; 2004, 7; 217-226
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The ichthyofauna of the degraded vendace lakes Mielno and Maróz studied with hydroacoustic and monitoring catch methods
    Autorzy:
    Świerzowski, A.
    Doroszczyk, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332411.pdf
    Data publikacji:
    2006
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    In 2005, the distribution, density, and structure of pelagic fish resources was studied in lakes Mielno (363 ha) and Maróz (332 ha) located in the Łyna catchment basin through which the Marózka River flows. The studies were conducted with a Simrad EY-500 echosounder (120 kHz, 7x7 deg, 0.3 ms, split beam version) and a pelagic trawl for monitoring catches. At the outset of the 1990s, vendace dominated the commercial catches of both lakes reaching about fifteen kgźha-1. Significant changes have occurred in the structure of the pelagic ichthyofauna in recent years in the studied lakes; the disappearance of vendace and the dominance of bleak and roach in the catches indicates that the tempo of eutrophication has increased.
    Źródło:
    Hydroacoustics; 2006, 9; 181-190
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Spatial variation in the occurence and density of pelagic fish in lake Lansk: monitoring with hydroacoustics and catch methods
    Autorzy:
    Świerzowski, A.
    Doroszczyk, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332644.pdf
    Data publikacji:
    2005
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    The study was conducted in Lake Lansk (surface area - 1042 ha, maximum depth - 53 m), in which the former dominant was vendace. Commercial catch results from the past decade indicate that there has been a seventy-two-fold decreased in vendace stocks. Hydroacoustic estimates indicate that there are 7.9 million fish in the pelagic zone. Approximately 93% of these inhabit the epilimnion (6.8 thousand fishźha-1), which is 7.6 times larger than that in the hypolimnion. There were 2.5 times fewer fish in a similarly sized southern region of the lake in 2004 than in 2001. Using the numbers, species structure, and individual weight, the biomass of the fish inhabiting the pelagic zone was calculated at 194.7 kgźha-1. The largest share was of vendace at 45.7% (89.0 kgźha-1), followed by roach at 18% (35.0 kgźha-1) and bleak at 13.1% (25.5 kgźha-1). The share of 0+ age group vendace was determined to be 70%. This might explain the decrease in commercial vendace catches caused by poor environmental conditions and overfishing. It also forecasts an improvement in resources of this species in the coming years.
    Źródło:
    Hydroacoustics; 2005, 8; 209-216
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Can we distinguish acoustically between vendace stock and stickleback stock in lake Pluszne?
    Autorzy:
    Doroszczyk, L.
    Długoszewski, B.
    Godlewska, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/331874.pdf
    Data publikacji:
    2010
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    Hydroacoustical monitoring of vendace stocks in lake Pluszne is performed regularly since 90-ties. However, in 2009 the lack of oxygen below the thermocline prevented fish to occupy the hypolimnion, which is its natural habitat. This led to a mixture of vendace and other fish species above the thermocline. The trawl catches accompanying hydroacoustical studies have contained exclusively vendace and stickleback. Investigation of TS have shown two-pick distributions, one corresponding to the size of vendace and one smaller. The two fish species were separated by thresholding. The maps of fish spatial distributions confirmed that vendace was present only in the deepest part of the lake, which is typical for this part of a year, while the other fish were distributed over the whole lake area. The worsening of environmental conditions in Lake Pluszne (increase of eutrophication) leads to declining vendace population.
    Źródło:
    Hydroacoustics; 2010, 13; 67-74
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Day/night effects of passing boat on fish distribution in the shallow Malta reservoir
    Autorzy:
    Godlewska, M.
    Długoszewski, B.
    Doroszczyk, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332556.pdf
    Data publikacji:
    2009
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Tematy:
    Malta Reservoir
    hydroacoustical measurements
    fish population
    Opis:
    Hydroacoustical measurements of fish population in the shallow Malta reservoir (mean depth <3 m) were performed in September and October 2008 using mobile horizontal beam. During the different time of day and night the same transects were covered in two directions, from the dam towards the upper part of the reservoir and back. During the day the number of fish registered on the returned way was lower than on the way forward in 83% of cases, and during the night in 67% of cases, however these differences were not statistically significant. Observation of fish at different distances from the boat have shown small avoidance reaction, especially for the small fish, that was similar during the day and at night, thus suggesting that mainly noise was responsible for the fish avoidance. Nevertheless, in shallow waters boat avoidance by fishes is of much less importance than in marine environment.
    Źródło:
    Hydroacoustics; 2009, 12; 61-68
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Comparison of acoustical estimates of fish abundance for different coverage and survey design
    Autorzy:
    Doroszczyk, L.
    Długoszewski, B.
    Godlewska, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/332469.pdf
    Data publikacji:
    2007
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    The aim of this paper is to investigate the influence of the degree of coverage, survey design, and method of calculation on fish abundance estimation results. Measurements were performed in deep, mesotrophic lake, containing fish community dominated by vendace (Coregonus albula L.). Two types of survey design were applied: the regular parallel transects with constant distance between them and the triangular (zig-zag) transects. It has been shown that at high enough degree of coverage both designs give equivalent estimates of fish abundance and similar fish distribution, however at lower coverage the parallel transects are preferable. With increasing degree of coverage the fish abundance increases as well until some asymptotic value, which is reached at degree of coverage equal to 0.8. The three different methods of estimating total stock have been applied: arithmetic mean, weighted mean, and kriging. The estimates of fish abundance received by the first two methods were very similar, while the third one was significantly lower.
    Źródło:
    Hydroacoustics; 2007, 10; 33-38
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Acoustical monitoring of fish at an electric barrier
    Autorzy:
    Godlewska, M.
    Doroszczyk, L.
    Długoszewski, B.
    Mokwa, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/331543.pdf
    Data publikacji:
    2008
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Tematy:
    acoustical monitoring
    fish
    electric barrier
    Opis:
    Acoustical monitoring of fish at an electric barrier was performed using EY 500 split beam echo-sounder with the transducer directed horizontally. Stationary measurements done during the operating barrier and when the electric power was switched off have shown statistically significant difference in the number of fish approaching the barrier, 11 fish in the first case, and over 280 in the second. The electric barrier affected more strongly large fish than the small ones. Mobile measurements performed in a basin from which fish were approaching barrier revealed the higher fish concentration just in front of the operating barrier than elsewhere.
    Źródło:
    Hydroacoustics; 2008, 11; 97-104
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-7 z 7

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