Methodological Pitfalls of Monitoring: Water Conditions Affect the Efficiency of Bottle Traps and Capture Success
by
, , and
Teodor J. Purger
1
,
Boldizsár Szűcs
1,
József Dezső
2,
László Wágner
3,
Dragica Purger
4,5 and
Jenő J. Purger
1,5,* 1
Department of Ecology, Institute of Biology, Faculty of Sciences, University of Pécs, Ifjúság útja 6, H-7624 Pécs, Hungary
2
Department of Physical and Environmental Geography, Institute of Geography and Earth Sciences, Faculty of Sciences, University of Pécs, Ifjúság útja 6, H-7624 Pécs, Hungary
3
Duna-Drava National Park Directorate, Tettye tér 9, H-7625 Pécs, Hungary
4
Institute of Pharmacognosy, Faculty of Pharmacy, University of Pécs, Rókus utca 2, H-7624 Pécs, Hungary
5
BioRes Limited Partnership, Barackvirág utca 27, H-7624 Pécs, Hungary
*
Author to whom correspondence should be addressed.
Biology 2025, 14(10), 1416; https://doi.org/10.3390/biology14101416
Submission received: 11 August 2025
/
Revised: 6 October 2025
/
Accepted: 10 October 2025
/
Published: 15 October 2025
(This article belongs to the Section Ecology)
Simple Summary
The Szaporca Old-Drava oxbow, one of Hungary’s earliest wetlands designated under Ramsar Convention, has faced significant threats due to drying. This necessitated the implementation of water replenishment measures. Our study aimed to assess the assemblage of aquatic vertebrates detectable by using bottle traps and to examine how water replenishment influences the traps’ efficiency and capture success. We found that the relative frequency of smooth newts caught with bottle traps was 10%, while that of other amphibian and fish species did not even reach 1%. Following the increase in water volume in the oxbow, both the efficiency of bottle traps (measured as the number of traps that captured smooth newts) and their capture success (number of caught newt individuals) declined significantly. The proportion of male smooth newts caught in traps increased significantly relative to females. Water replenishment also altered flow conditions and increased the extent of inundated areas, which in turn changed the substrate beneath the bottle traps. These environmental changes likely contributed to variations in trap performance. Our finding suggests that both water volume and associated habitat modifications can significantly influence the outcome of monitoring efforts using passive trap methods.
Abstract
Wetland diversity and associated wildlife is declining globally. The Szaporca Old-Drava oxbow, one of Hungary’s first wetlands designated under the Ramsar Convention, has been threatened by desiccation, prompting the implementation of water replenishment interventions. This study aimed to determine which aquatic vertebrate species can be detected using bottle traps in the oxbow and whether the traps’ efficiency and capture success change following hydrological restoration. Our results showed that the relative frequency of smooth newts caught with bottle traps was 10%, while that of other amphibians (Danube crested newt, common spadefoot toad, edible frog) and fish (European weather loach, European mudminnow, Danube whitefin gudgeon) species did not even reach 1%. Based solely on the relative frequency data of the smooth newt, we found that both the capture efficiency (10.4% vs. 3%) and capture success (17% vs. 7.4%) of bottle traps significantly declined following an increase in water volume in the oxbow. Sex ratio patterns also shifted markedly: in the year of water scarcity, the male-to-female ratio of smooth newt was 2.7:1, whereas during water-abundant conditions it increased to 7:1. Water replenishment raised the water level by nearly one meter, resulting in the partial inundation of terrestrial vegetation and consequent habitat alterations. While water supplementation clearly supports the persistence of rare, protected, strictly protected and endemic aquatic species, our findings highlight the importance of considering hydrological conditions when interpreting the results of long-term monitoring in wetland ecosystems.
