Electrofishing in streams of low water conductivity has technical limitations leading to the widespread use of poison fishing. In theory, provided a high enough voltage gradient can be created in water, electrofishing should be possible in all but the lowest of conductivities (<10 µS/cm). Using custom‐made equipment delivering up to 1,500 V DC, tests were carried out in French Guiana on 27 streams with water conductivity as low as 16 µS/cm. Approximately 5,800 fish of 93 species were captured, with an electrofishing mortality rate of 1.83%. Poison treatments were used within enclosed sections to assess how efficient multiple pass electrofishing removal is when assessing species richness and population number. The Chao II estimator on 2 electrofishing passes gave the best results for species richness, but rare species can elude electrofishing. Estimates of total fish abundance (i.e. all species pooled) were possible with the use of depletion models. Capture efficiencies by species were highly biased, however, and abundance could be underestimated for the most difficult species to catch. These results show that with the right equipment and settings, electrofishing can be an efficient alternative to poison fishing surveys in small tropical streams of low water conductivity but high biodiversity value.

International audienceExotic invasive species are one of the major threats for aquatic ecosystems. However, the interactions between exotic plants and exotic herbivores have been little studied, despite their role in invasion success. Here, we tested how interactions between an invasive plant and an invasive herbivore could affect their own growth and their colonization abilities in freshwater ecosystems. Ludwigia grandiflora and Procambarus clarkii, two exotic invasive species which co -occur in some French wetlands, were used for our laboratory experiment and field survey. Although L. grandiflora was consumed by crayfish, its growth was not significantly affected by crayfish density. Indeed, the final living biomass of L. grandiflora was similar to those of controls, despite significant losses induced by crayfish. Furthermore, L. grandiflora became more fragmented in the presence of a high density of P. clarkii, which might increase its dispersal abilities. In addition, our field survey revealed that the abundance of crayfish was higher in a patch invaded by L. grandiflora than in an uninvaded patch. Thus, the outcome of the interaction between the invasive plant and the invasive crayfish, via its positive effect on the invasion dynamics of these two species, could have dramatic consequences for native communities of freshwater ecosystems

Performing fish survey protocols with different electrofishing equipment and settings can lead to difficulties in comparing the data obtained. In this study, we captured two fish taxa (i.e. the European eel and salmonids: Atlantic salmon and brown trout) in the field using four models of electrofishers that provided different waveforms: direct current (DC), pulsed direct current (PDC) and pulsed exponential current (PEC). This study aimed to assess effects of using different waveforms and frequencies, while considering environmental variables, on i) attraction, represented by occurrence and catch-per-unit-effort (CPUE) of fishes, and ii) spinal damage, based on ultrasound of the spinal column. For all species, DC and PDC yielded equivalent occurrences and CPUEs, regardless of the frequency. In contrast, PEC induced a significant decrease in occurrences and CPUEs of both eels and salmonids. The percentage of injured fishes increased as the frequency or length of the salmonids increased while waveform had no effect. Ultrasound was determined to be a good non-invasive method to detect injuries in fishes.

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