Abstract
Aphanius iberus is an endemic cyprinodontoid fish species of Mediterranean ponds in danger of extinction. In this study, we studied some abiotic and biotic factors that can influence A. iberus’s size structure and density in Mediterranean brackish ponds. We sampled fish using fyke nets in 10 ponds of Empordà (Spain) during the spring season. Our results showed that a better ecological status (according to the Water Quality of Lentic and Shallow Ecosystems (QAELS) index), pond’s depth and pond’s isolation (reflected by an increase in total nitrogen) were related to larger individual sizes and more size-diverse populations. Increasing the salinity is known to help the euryhaline A. iberus acting as a refuge from competitors. Nevertheless, our results showed that higher conductivities had a negative effect on A. iberus’s size structure, leading to a decrease in the mean and maximum size of the fish. Fish abundance (expressed as captures per unit of effort (CPUE)) seemed to increase with increasing the pond’s depth and total nitrogen (the latter reflecting pond isolation). In conclusion, our results suggest that achieving a better pond ecological status may be important for the conservation of endangered A. iberus, because better size-structured populations (i.e., larger mean and average lengths) were found at higher water quality conditions.
Highlights
Aquatic ecosystems of the Iberian Peninsula are a hotspot for endemic freshwater fish fauna; still, most of the fish species are critically threatened by habitat destruction, intensive agricultural activities or the introduction of exotic species [1,2]
Some studies have shown that the abundance and size structure of A. iberus depends on the ecological status of the ponds, with larger individuals and higher densities found in ponds with a higher water quality [15]
The present study aims to identify the factors influencing the abundances and population size structure of A. iberus in the north-east of the Iberian Peninsula in late-spring
Summary
Aquatic ecosystems of the Iberian Peninsula are a hotspot for endemic freshwater fish fauna; still, most of the fish species are critically threatened by habitat destruction, intensive agricultural activities or the introduction of exotic species [1,2]. Some studies have shown that the abundance and size structure of A. iberus depends on the ecological status of the ponds, with larger individuals and higher densities found in ponds with a higher water quality [15]. The present study aims to identify the factors influencing the abundances and population size structure of A. iberus in the north-east of the Iberian Peninsula in late-spring (i.e., when this species finishes the first period of annual reproduction). We assessed whether abiotic factors (i.e., conductivity, nutrient concentrations and pond morphology); the ponds’ ecological status; food resource availability (zooplankton biomass) and the presence of the main competitor, Gambusia holbrooki, are correlated with the size structure and abundance of this endangered species in 10 coastal brackish and hypersaline ponds. We would expect that the abundance of A. iberus would be negatively correlated with the zooplankton biomass due to fish predation on zooplankton
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