Seven sites on three tributaries with intermittent flow regimes in the middle reaches of the Guadiana, i.e. Xévora, Caia and Degebe, were sampled approximately every 3 months from April 1995 to April 1997. The density and biomass of fish were greater in downstream rivers and sites. Along the Xévora River, a series of point abundance samples showed evidence of fish zonation along the river. Canonical correspondence analysis (CCA) suggested a simple relationship between the different species and their preferred habitat. The small‐sized Rutilus alburnoides and Leuciscus pyrenaicus used most or all of the habitats with some cover and flowing water. Greater concentrations of larger fish were found in downstream reaches which generally had greater depths as stream width increased: large Barbus microcephalus, B. steindachneri and B. comiza preferred such sites on the Degebe River. Droughts in seasonal Mediterranean streams such as the Guadiana River are a predictable natural disturbance. In the summer, flow ceases and some stretches of river consist of isolated pools. This results in intense aggregations of fish and possible competition for food and/or space. Although some species are well adapted to natural droughts, habitat degradation and possibly the introduction of exotic species contribute to marked variability in species composition.

No abstract

The taxonomy of the genus Leuciscus in the Iberian Peninsula has been presented on the basis of morphological analysis. Two species are believed to occur in Portuguese inland waters, L. carolitertii, the northern basins chub, and L. pyrenaicus, which was described for the Tejo and southern basins. Since only slight differences in the meristic and morphometric characters are observed, the distinction between the two species has been made previously mainly on the basis of osteology. In order to investigate the patterns of genetic differentiation between these species, 24 sites were sampled for both species, and examined electrophoretically for the study of variation at 27 presumptive loci. The results pointed to different levels of population differentiation among drainages and support the recognition of the species level for L. pyrenaicus and L. carolitertii. Our results also suggested that the distribution area of L. pyrenuicusis probably restricted to Tejo and to the small drainages near Tejo, while L. carolitertiiseems to have a widespread distribution area, including Lima, Douro, Vouga, Mondego, Guadina and Sado drainages. Moreover, concerning the southern populations, Mira and Arade, the surprisingly high level of differentiation observed at several loci, supports the existence of a further species occurring in these small drainages. The evolutionary aspects related to that differentiation are discussed. 8 1995 The Fishenes Society of the British Isles

In this paper we extend the definition of the influence function to functionals of more than one distribution, that is, for estimators depending on more than one sample, such as the pooled variance, the pooled covariance matrix, and the linear discriminant analysis coefficients. In this case the appropriate designation should be ''partial influence functions,'' following the analogy with derivatives and partial derivatives. Some useful results are derived, such as an asymptotic variance formula. These results are then applied to several estimators of the Mahalanobis distance between two populations and the linear discriminant function coefficients.

Pires DF, Pires AM, Collares‐Pereira MJ, Magalhães MF. Variation in fish assemblages across dry‐season pools in a Mediterranean stream: effects of pool morphology, physicochemical factors and spatial context. Ecology of Freshwater Fish 2010: 19: 74–86. © 2009 John Wiley & Sons A/S Abstract –  Knowledge of patterns of refuge use by fish is critical for maintaining biodiversity in drought‐prone streams. In this study, the fish assemblages of 21 dry‐season pools in a Mediterranean stream were characterised and related to three sets of factors reflecting pool morphology, physicochemistry and spatial context. Fish were associated with the three sets of variables, with variation partitioning indicating that overall species richness and abundance were primarily related to pool morphology but relative species abundances were mainly associated with physicochemical contexts. In general, species richness was the highest but overall fish abundance was the lowest in large pools. Pools well shaded by riparian canopy held the highest richness and abundance of native fish, but relative species abundances and assembly structure varied among pools contingent on canopy cover, substrate composition and spatial location. These results suggested that conservation of fish diversity in Mediterranean streams requires networks of pools with diverse sizes and physicochemical contexts.