| Summary: | Population size structure can provide insights in species-specific knowledge and fish management. The purpose of the present study is to assess the influence of hydrological flow variability along the longitudinal gradient in the population size structure metrics of three non-native fish species widely distributed in the Iberian Peninsula, Alburnus alburnus L., Lepomis gibbosus L. and Gobio lozanoi Doadrio & Madeira, 2004. We analysed populations at site level (29 sampling localities in fluvial sectors) along the longitudinal gradient in the main rivers of the Segura River basin, which is one of the most regulated basins in the Iberian Peninsula. The total of 3265 specimens (1636 A. alburnus, 349 L. gibbosus and 1280 G. lozanoi) caught during autumns was measured in situ for length. We explored nine population size metrics (average, median, maximum, minimum, size range, variance, coefficient of variation, skewness and kurtosis of Fork Length).
Population size metrics significantly differed at site level and at sector level. Sampling sites directly influenced by a potential refuge of the large reservoirs showed a higher variance in the population size structure of A. alburnus and L. gibbosus, but less variance in the G. lozanoi populations. In fact, flow regulation and the presence of fish refuges to higher discharges have been shown as significant factors to explain the variability in several population size metrics.
Documented changes in fish size metrics at population levels can demonstrate trends in non-native fishes at basin scale, however, the collinearity with spatial gradients and the species-specific response could make it a difficult undertaking.
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