The size selectivity of the main body of a sampling pelagic pair trawl in freshwater reservoirs during the night

Říha, Milan; Jůza, Tomáš; Prchalová, Marie; Mrkvička, Tomáš; Čech, Martin; Draštík, Vladislav; Muška, Milan; Kratochvíl, Michal; Peterka, Jiří; Tušer, Michal; Vašek, Mojmír; Kubečka, Jan

doi:10.1016/j.fishres.2012.04.012

Cited by 13 publications

(6 citation statements)

References 23 publications

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“…Its length is 9 km, mean depth 16 m, maximum surface area 210 ha, and the volume is 33 × 10 6 m 3 . The reservoir has served as a freshwater store for České Budějovice and adjacent localities (Říha et al., ). The local early juveniles communities are dominated by cyprinids but percids, particularly perch and pikeperch ( Sander lucioperca : Percidae, L.), are also important components (Jůza et al., ; Jůza et al., , Jůza et al., ).…”

Section: Introductionmentioning

confidence: 99%

Are diel vertical migrations of European perch (Perca fluviatilis L.) early juveniles under direct control of light intensity? Evidence from a large field experiment

et al. 2018

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Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic environment. A general pattern of DVMs has been well described, particularly in European perch (Perca fluviatilis), but whether the migrations are directly controlled by light and what is the ultimate cause of the diel vertical shifts, remains poorly understood. Undertaking a large‐scale field experiment in a thermally stratified, canyon‐shaped reservoir, we demonstrated for the first time that DVMs of a bathypelagic early juveniles community, dominated by European perch larvae and juveniles prior the metamorphosis, were under direct control of the light intensity; that is, they did not operate as a genetically fixed behaviour. Prior to the experiment, the depth distribution of the bathypelagic perch early juveniles was strongly correlated with the light intensity on the water surface (p < .001). The community underwent regular DVMs between the epilimnion (depth <2.0 m) and hypolimnion (depth >3.0 m) reaching a maximum amplitude of 13 m. Hydroacoustic recordings by the echosounder SIMRAD EK 60 (120 and 400 kHz) showed that during the experiment, when the surface was covered with a large black non‐transparent foil (2500 m2; simulated conditions of complete and constant darkness), the regular vertical movement of the bathypelagic perch early juveniles was interrupted and the community occupied the epilimnion constantly for 24 hr. Immediately after the foil was removed at midday, the bathypelagic perch early juveniles were exposed to a steep increase in light intensity (from <1 LUX to >100 × 103 LUX) and they escaped into the hypolimnion where they were safe from visual predation which took place in the bright surface layers (epilimnion particularly). Our findings imply that occupying a deep, dark refuge in the daytime is essential for the survival of perch in their early life stage.

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Section: Introductionmentioning

confidence: 99%

Are diel vertical migrations of European perch (Perca fluviatilis L.) early juveniles under direct control of light intensity? Evidence from a large field experiment

et al. 2018

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“…Pelagic trawling and purse seining were used at night in the pelagic zone to obtain independent estimates of the length frequency distributions and biomass of the whole fish community. To obtain an unbiased sample of fish length-frequency distribution, density estimates of small fish (≤180mm) were obtained by purse seining and those of larger fish (>180mm) were obtained using the trawl [ 31 ]. This approach was chosen because of recent findings that the trawl used underestimates the fish density up to 180 mm SL [ 31 ].…”

Section: Methodsmentioning

confidence: 99%

“…To obtain an unbiased sample of fish length-frequency distribution, density estimates of small fish (≤180mm) were obtained by purse seining and those of larger fish (>180mm) were obtained using the trawl [ 31 ]. This approach was chosen because of recent findings that the trawl used underestimates the fish density up to 180 mm SL [ 31 ]. The trawl opening width was 12–13.5m, and the opening height was 8m.…”

Section: Methodsmentioning

confidence: 99%

Biomass and Abundance Biases in European Standard Gillnet Sampling

et al. 2015

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The European Standard EN 14757 recommends gillnet mesh sizes that range from 5 to 55mm (knot-to-knot) for the standard monitoring of fish assemblages and suggests adding gillnets with larger mesh sizes if necessary. Our research showed that the recommended range of mesh sizes did not provide a representative picture of fish sizes for larger species that commonly occur in continental Europe. We developed a novel, large mesh gillnet which consists of mesh sizes 70, 90, 110 and 135mm (knot to knot, 10m panels) and assessed its added value for monitoring purposes. From selectivity curves obtained by sampling with single mesh size gillnets (11 mesh sizes 6 – 55mm) and large mesh gillnets, we identified the threshold length of bream (Abramis brama) above which this widespread large species was underestimated by European standard gillnet catches. We tested the European Standard gillnet by comparing its size composition with that obtained during concurrent pelagic trawling and purse seining in a cyprinid-dominated reservoir and found that the European Standard underestimated fish larger than 292mm by 26 times. The inclusion of large mesh gillnets in the sampling design removed this underestimation. We analysed the length-age relationship of bream in the Římov Reservoir, and concluded that catches of bream larger than 292mm and older than five years were seriously underrepresented in European Standard gillnet catches. The Římov Reservoir is a typical cyprinid-dominated water body where the biomass of bream > 292mm formed 70% of the pelagic trawl and purse seine catch. The species-specific relationships between the large mesh gillnet catch and European Standard catch suggested that the presence of carp (Cyprinus carpio), European catfish (Silurus glanis), tench (Tinca tinca) or bream warrants the use of both gillnet types. We suggest extending the gillnet series in the European Standard to avoid misinterpretation of fish community biomass estimates.

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“…However, these traditional methods may offer inaccurate or misleading information (Hubert et al, 1996). Accordingly, these methods are selective and the accuracy relies on gear saturation and fish activity (Bethkea et al, 1999; Prchalová et al, 2010; Říha et al, 2012). Moreover, the traditional method makes the fish experience repetitive stress that may influence their growth and mortality (Conti et al, 2006) and requires more workers adding up to the operational costs.…”

Section: Introductionmentioning

confidence: 99%

Hydroacoustic assessment of standing stock of Nile tilapia ( Oreochromis niloticus ) under 120 kHz and 200 kHz split‐beam systems in an aquaculture pond

Liu

Setiazi

2021

Aquaculture Research

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Tilapia production is one of the most diversified fish sectors globally and is expected to continually grow. In Taiwan, Nile tilapia (Oreochromis niloticus) is the second most produced fish species in the aquaculture industry. Traditionally, fishermen would use a net to estimate the volume of the fish species in the, pond but this method offer numerous disadvantages and acoustic methods were proven to be reliable in fisheries resource survey. Thus, this study explored an acoustic method to measure the standing stock and biomass in a Nile tilapia aquaculture pond. A rectangular tank (2.3 × 0.82 × 0.66 m) with a set of echo sounders (frequencies: 120 and 200 kHz) fixed on a steel frame was utilized to approximate the target strengths of Nile tilapia samples (n = 35) in lateral positions. Findings reveal that the estimated target strength using the two beam frequencies did not differ significantly (p > 0.05). A horizontal conversion equation in lateral position was established, which was used for biomass backscattering analysis of Nile tilapia in fish ponds. The results show that 120 kHz frequency can accurately predict Nile tilapia fish biomass in an aquaculture pond. This study has determined a species‐specific equation for the hydroacoustic method to enable a more accurate estimation of fish biomass, such as that of Nile tilapia. Fish biomass estimation will enhance aquaculture management, such as optimizing capital invested and minimizing overfeeding.

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The size selectivity of the main body of a sampling pelagic pair trawl in freshwater reservoirs during the night

Cited by 13 publications

References 23 publications

Are diel vertical migrations of European perch (Perca fluviatilis L.) early juveniles under direct control of light intensity? Evidence from a large field experiment

Are diel vertical migrations of European perch (Perca fluviatilis L.) early juveniles under direct control of light intensity? Evidence from a large field experiment

Biomass and Abundance Biases in European Standard Gillnet Sampling

Hydroacoustic assessment of standing stock of Nile tilapia ( Oreochromis niloticus ) under 120 kHz and 200 kHz split‐beam systems in an aquaculture pond

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