Empirical Estimation of Accumulation-Induced Change in Gill Net Catchability:
Mind the Observation Errors

Marjomäki, Timo J.; Paloniemi, Marko; Keskinen, Tapio; Kuha, Jonna

doi:10.2174/1874401x01508010013

Cited by 3 publications

(2 citation statements)

References 23 publications

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“…Beyond the invasive, laborious, and expensive nature of gillnet sampling, limitations include its dependency on fish activity, differences in the catchability of species [ 92 ], underestimation of small size classes [ 69 ], and the fact that catch data indicate only relative abundance [ 27 , 28 , 93 ]. The efficacy of the method can be influenced by mesh congestion, declining as the number of fish trapped increases [ 94 , 95 ]. During daytime in clear water, even small numbers of entangled fish can reduce further catch significantly [ 25 ].…”

Section: Discussionmentioning

confidence: 99%

Obtaining accurate population estimates with reduced workload and lower fish mortality in multi-mesh gillnet sampling of a large pre-alpine lake

Bader,

Gaye-Siessegger,

Scholz

et al. 2024

PLoS ONE

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The EU Water Framework Directive requires monitoring of the ecological status of lakes, with fish as a relevant class of biotic quality indicator, but monitoring fish populations in large lakes is demanding. This study evaluated use in Lake Constance of a novel multi-mesh gillnet modified to reduce catch numbers. In direct comparison with conventional European Committee for Standardization (CEN) nets we achieved 48% reduction in fish mortality with 38% less labour for tasks directly influenced by fish catch numbers, while maintaining comparable species composition and catch per unit effort. Comparison of mesh sizes indicated no significant reduction in species detection in area-reduced panels of the small mesh sizes, while total observed species richness was greater when using the modified nets. Differences in benthic species communities among depth strata were common, while those of pelagic zones were more homogeneous and did not differ significantly with depth. Catches of different net types from the same depth stratum did not exhibit significant differences. The dominance structure of the most common species, relevant to lake assessment, was similar in catches of both net types, suggesting overall superiority of the modified nets in Lake Constance. Sampling conducted according to standard European CEN protocol, while deploying 60% fewer nets, yielded sufficiently precise abundance estimates for monitoring shallow areas of the benthic zone. A 50% difference in the abundance of dominant species was detected among sampling events with a certainty of 95%. The sample did not provide comparable accuracy in deep benthic strata or the pelagic zone, but was adequate to record complete inventories of species present. Based on this trial data, a new stratified sampling design is proposed for monitoring large lake fish communities for ecological assessment. Depth-dependent fish communities were used to calculate the required number of nets, which resulted in a 69% reduction for the entire lake compared to the CEN calculation method. Using the modified nets increases the feasibility of performing WFD surveys, by reducing effort and cost, while the simultaneous halving of fish mortality minimises the negative impact of fish surveys.

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Section: Discussionmentioning

confidence: 99%

Obtaining accurate population estimates with reduced workload and lower fish mortality in multi-mesh gillnet sampling of a large pre-alpine lake

Bader,

Gaye-Siessegger,

Scholz

et al. 2024

PLoS ONE

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show abstract

“…Because it is difficult to sample with gillnets the smallest and the largest fish, the correlation would have more significant in excluding these sizes. Furthermore, bias induced by accumulation of fish during gillnet sampling must be taken into account to avoid reduction in its catchability (Marjomäki, ).…”

Section: Discussionmentioning

confidence: 99%

Seasonal inter-calibration between acoustic and multi-mesh gillnets sampling for fish biomass assessment in reservoirs

Laouar

Djemali

2018

J Appl Ichthyol

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Summary This paper presents the results of an inter‐calibration between acoustic and gillnets sampling in two North African reservoirs according to seasons. Gillnets with multi‐mesh were designed for sampling fish in lakes while acoustic surveys were performed with a split beam Simrad EK60 echosounder. Sampling events were carried out during summer (September 2015), autumn (December 2015), winter (March 2016) and spring (June 2016) in two Tunisian reservoirs (Kasseb and Siliana) with different depths and shapes. Gillnet catches showed a high proportion of barbell whatever the seasons in Kasseb Reservoir, while at Siliana Reservoir, significant seasonal changes in relative abundances have been evidenced. The highest fish biomass of the entire water column was observed in winter daytime (103 kg/ha) in Kasseb Reservoir and in summer daytime (283 kg/ha) in Siliana Reservoir. Average biomass observed in autumn (December) for the two reservoirs were lower than the other seasons. During spring, density daytime values in Kasseb were higher than during nighttime while it was the opposite in summer and autumn. Fish densities detected in Kasseb Reservoir in vertical beaming was higher than those detected in horizontal beaming (p < .05). The longitudinal distribution of fish in the reservoirs showed that there is no clear trend in fish densities according to strata. High numbers of fish were detected in deep strata and big fish were located in the surface water near the dam of Kasseb Reservoir. A significant linear correlation was showed between acoustic density/NPUE and acoustic biomass/BPUE but the perfect correlation with the 1:1 fit was showed only between acoustic biomass/BPUE.

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Collaborative research enhances selectivity in a lake fishery

Sandström,

Norrgård,

Axenrot

et al. 2024

Fisheries Management Eco

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Size and species selectivity are crucial for developing sustainable fisheries. Our objective was to estimate the selectivity of whitefish fisheries in a large European lake through a collaboration of fishers, regional managers, and scientists. Fishers were given special permits to test, within a common framework and together with scientists, selectivity enhancement strategies adapted to their own experiences. Fishers and scientists jointly tested gillnets and pontoon traps and how fishing depth, soak time, fishing season, and mesh size were affected by bycatches of undersized fish of sensitive species. Results indicated that the selectivity of the fishery could be increased, particularly by targeting whitefish adjacent to spawning sites where spatiotemporal overlap with bycatch species was lower. Proposed changes to the fishery, such as new gear, would be costly initially but could become profitable over time due to a lower cost of handling bycatch. Our findings demonstrated that co‐constructed knowledge can contribute to the governance of aquatic resources.

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Empirical Estimation of Accumulation-Induced Change in Gill Net Catchability: Mind the Observation Errors

Cited by 3 publications

References 23 publications

Obtaining accurate population estimates with reduced workload and lower fish mortality in multi-mesh gillnet sampling of a large pre-alpine lake

Obtaining accurate population estimates with reduced workload and lower fish mortality in multi-mesh gillnet sampling of a large pre-alpine lake

Seasonal inter-calibration between acoustic and multi-mesh gillnets sampling for fish biomass assessment in reservoirs

Collaborative research enhances selectivity in a lake fishery

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