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The ichthyofauna of the degraded vendace lakes Mielno and Maróz studied with hydroacoustic and monitoring catch methods

Świerzowski A., Doroszczyk L.

Hydroacoustics

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2006

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Vol. 9

181-190

EN

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.

2

Spatial variation in the occurence and density of pelagic fish in lake Lansk: monitoring with hydroacoustics and catch methods

Świerzowski A., Doroszczyk L.

Hydroacoustics

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2005

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Vol. 8

209-216

EN

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.

3

Can we precisely estimate fish sizes using acoustics?

Godlewska M., Świerzowski A., Menshutkin V., Wanzebock J.

Hydroacoustics

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2005

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Vol. 8

53-60

EN

Fish target strength (TS) is the key quantity in the acoustic assessment of fish abundance and biomass. Since TS is the function not only of fish length, but also depends on species, physiological state, behavior, and environmental parameters, calculation of fish real length on the basis of acoustical data is not a trivial task. Commonly fish size distribution is estimated from TS distribution using Love’s formula. In the present paper fish target strengths for typical European freshwater species were determined experimentally and based on these results a mathematical model has been constructed. The model accounts for the TS/L relationship for a given species and for fish behavior. From the single fish measurements in cages three types of fish behavior were distinguished and incorporated into the model. Fish size distributions resulting from the model were compared with those obtained using directly Love’s formula and from the net catches.

4

Seasonal differences in situ measurements of the target strength of vendace (Coregonus albula L.) in lake Pluszne

Świerzowski A., Doroszczyk L.

Hydroacoustics

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2004

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Vol. 7

217-226

EN

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.

5

Pattern of spatial fish distribution in the sulejow reservoir monitored by horizontally beaming echosounder and by gill netting

Frankiewicz P., Świerzowski A.

Hydroacoustics

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2004

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Vol. 7

37-45

EN

The Sulejów reservoir situated on the Pilica River in Central Poland serves as an important source of drinking water for the Lodz Agglomeration. Precise knowledge on fish abundance, community structure as well as spatial and temporal changeability is crucial for proper fishery management (biomanipulation) in order to slow down the reservoir eutrophication and prevent toxic algal blooms. As the reservoir is very shallow (average depth is 3.3 m) it was necessary for fish distribution monitoring to apply, first time in Poland, horizontally looking split beam echosounder (Simrad EY-500 with elliptic transducer ES 120-4x10). Simultaneously, to collect fish for verification of acoustic data and determination of fish species composition, multimesh gill nets were used in representative parts of the reservoir. Prepared maps showing both spatial fish distribution and their density suggest that used methods were suitable for identification of specific areas characterized by different quality of environmental conditions.

6

The variability of spatial distribution and density of fish in the Klimkówka dam reservoir

Świerzowski A.

Hydroacoustics

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2003

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Vol. 6

69--78

EN

The Klimkówka Dam Reservoir is situated on the Ropa River in southern Poland. The surface area of the reservoir is about 306 ha and its capacity is 43.5 hm3. Acoustic surveys were conducted both in the daytime and at night using a SIMRAD EY-500 split beam 120kHz echo sounder. Maps of the spatial distribution and density of fish were drawn up, and the fish species structure, size, number and biomass were estimated based on acoustic surveys and supervised net catches. The highest fish density at night occurred in the river tributary zones (836 fish/ha). In this area at night fish density was twice as high as in the central region of the reservoir. The density figure for the whole reservoir was 638 fish/ha and was 1.4 limes higher than that in the Solina Reservoir and from ten- to twenty-fold lower than in several other studied lakes. Fish catches performed with pelagic trawIs and net sets revealed the presence of nine fish species. Lake and river trout species which had been introduced to the reservoir were not noted. The fish biomass was estimated to be 11.5 tons, or 44.4 kg/ha, and was from three to 14 times lower in comparison to the estimated figure in several other lakes.

7

In situ measurements of the target strength of vendace (coregonus albula 1.) in lake Pluszne

Świerzowski A., Godlewska M.

Hydroacoustics

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2003

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Vol. 6

59--68

EN

The paper presents a preliminary discussion of the results of the first Polish attempt to estimate the in situ target strength TS (dB). The subject of the study was the freshwater fish vendace Coregonus albula L. This species is a typical planktivore which inhabits the pelagic zone of Lake Pluszne (903 ha area, 51 m maximum depth) located in northeastern Poland. A Simrad EY-500 type split beam echosounder at a frequency of 120kHz and with a beam width of 7x7 degrees and pulse duration of 0.3 ms was used for acoustic measurements. The trace tracking method with an EP 500 program were used to analyse the data. Control fishing in various water layers was conducted made using pelagic trawl. The dependencies of TS (dB) on fish body length L (cm) were determined for the average values of TSS.A. = 20 log L -66.8 ± 0.3 SE, TSS.A. traces = 20 log L - 66.4 ± 0.2 SE and TSmax = 20 log L -65. 7 ± 0.3 SE.

8

The effect of the seasonal changes of environment on the hydroacoustically monitored spatial distribution and density of vendace (Coregonus albula L.) in Pluszne lake

Świerzowski A., Godlewska M.

Hydroacoustics

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2001

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Vol. 4

231--236

EN

Vendace (Coregonus albula L.) is an ecologically important element in the ecosystem of low trophy deep lakes. Investigations were carried out in Pluszne lake (surface area 900 ha, maximal depth 51 m) using Simrad EY-M (70 kHz) and EY 500 split beam (120 kHz) echosounder. Fish species identification was based on pelagic trawling. Water temperature and dissolved oxygen content were measured at 1 meter depth intervals. In June oxygen saturation of the upper hypolimnion reached nearly 100% while in October it dropped to 8% and approached the sublethal level for fish. The autumnal thermal and oxygen stratification caused that 80% of the fish became trapped in 10 m water stratum. The 20-fold decrease in the living and feeding space area for coregonids in autumn was the likely cause of their weakened condition and low reproduction. This happens directly preceding spawning and is the probable cause of decreased occurrence, or even disappearance of coregonids from many lakes.

9

Fish abundances and size structure distributions in reservoirs with different trophy level

Godlewska M., Świerzowski A.

Hydroacoustics

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2001

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Vol. 4

65--68

EN

Hydroacoustical estimation of fish abundance and distribution was performed in three reservoirs with different levels of eutrophication. To analyse TS distribution the echo counting method was applied with TVG set to 40 logR. The Biosonics 101 dual beam echosounder, frequency of 420 KHz, was used for measurements and the ESP software for acoustical data analyses. In the mesotrophic Solina reservoir fish abundance was an order of magnitude lower than in the other two eutrophic reservoirs. Also the fish length distributions had different shapes in al! three reservoirs indicating the changes in fish size structure due to eutrophication. Comparison of the above results shows that hydroacoustically collected data may help to assess the ecological state of inland waters and be used together with other methods in monitoring the water quality.

10

Hydroacoustical estimation of fish abundance and distribution in the Solina reservoir

Godlewska M., Półtorak T., Świerzowski A.

Hydroacoustics

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2000

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Vol. 3

169--172

EN

On the basis of hydroacoustical measurements performed in Solina reservoir from May to September 1999 the mean abundance was estimated at 0.7 fish per 1000 m3, and thus very low. Clear seasonal changes in fish vertical distributions, related to the hydrological parameters of the water were observed. Majority of fish performed diurnal vertical migrations to the productive surface water at night.

11

The effect of underwater noise emitted by motor boats on fish behaviour

Świerzowski A.

Hydroacoustics

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1999

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Vol. 2

33--38

EN

The aim of the study was lo determine susceptibility and avoidance behaviour of same freshwater fish exposed to underwater noise emitted by motor boats, most of all by the fishing boats with a Mariner motor (200 HP). The experimental station lo study fish responses was located in Lake Narie. Pikeperches, breams and carps were placed in a net cage and exposed to noise emitted by an underwater loudspeaker, noise duration and its characteristics being pre-established. Fish behaviour was registered on a video tape and stored in form of files related lo selected sequences. Pikeperch and bream did not show significant behavioural changes compared to the control periods. Carp, on the other hand, showed a noticeable and spontantaneous reaction, consisting of a 6-fold increase of the swimming speed. Adaptation period to noise of maximal volume was about 20 sec. It can be expected that in the conditions of the Vistula Lagoon, the minimal fish reaction will take place at a distance of about 150 m, while escape reaction should occur at 20 to 50 m. It is proposed to limit the speed of motor boats over fish spawning grounds and migration routes.