Twenty-five introduced fish species are established in Spanish fresh waters. Most of the introductions took place after 1900, with a significant exponential increase during the second half of the 20th century (15 species introduced from 1949). Major stocking efforts in Spanish waters have been suspended, but recently some species have been released by anglers or are suspected to be escapes from fish farms. Stream regulation is considered to be one of the main negative factors affecting river ecosystems in Spain, but many of the aliens adapt well to these altered habitats. Competition between native and exotic fishes is certain to occur to some degree, but there is little quantitative information. Fish conservation and fishery management must not be based on the ' introduce anything ' sentiment that has developed over more than a century. Information, education and public awareness are critical components of any effort to prevent the spread of introduced fish species. 2001 The Fisheries Society of the British Isles

Freshwater ecosystems are seriously imperiled by the spread of non-native fishes thus establishing profiles of their life-history characteristics is an emerging tool for developing conservation and management strategies. We did a first approach to determine characteristics of successful and failed non-native fishes in a Mediterranean-climate area, the Iberian Peninsula, for three stages of the invasion process: establishment, spread and integration. Using general linear models, we established which characteristics are most important for success at each invasion stage. Prior invasion success was a good predictor for all the stages of the invasion process. Biological variables relevant for more than one invasion stage were maximum adult size and size of native range. Despite these common variables, all models produced a different set of variables important for a successful invasion, demonstrating that successful invaders have a combination of biological traits that may favor success at all invasion stages. However, some differences were found in relation to published studies on fish invasions in other Mediterranean-climate areas, suggesting that characteristics of the recipient ecosystem are as relevant as the characteristics of the invading species.

Current climate change exacerbates the environmental restrictions on temperate species inhabiting low latitude edges of their geographical ranges. We examined how temperature variations due to current and future climate change are likely to affect populations' persistence of stream-dwelling brown trout Salmo trutta at the vulnerable southern periphery of its range. Analysis of 33 years of air temperature data by time-series models indicated a significant upward trend and a pronounced shift in air temperature around 1986-1987. This warming is associated with an ongoing population decline of brown trout, most likely caused by a loss of suitable thermal habitat in lower latitudes since the 1980s. Population decrease may not be attributed to physical habitat modification or angler pressure, as carrying capacity remained stable and populations were not overexploited. We developed regional temperature models, which predicted that unsuitable thermal habitat for brown trout increased by 93% when comparing climate conditions between 1975-1986 and 1993-2004. Predictions from climate envelope models showed that current climate change may be rendering unsuitable 12% of suitable thermal habitat each decade, resulting in an overall population decrease in the lower reaches of around 6% per year. Furthermore, brown trout catches markedly decreased 20% per year. Projections of thermal habitat loss under the ecologically friendly B2 SRES scenario showed that brown trout may lose half of their current suitable habitat within the study area by 2040 and become almost extinct by 2100. In parallel to the upstream movement of brown trout thermal habitat, warm water species are increasing their relative abundance in salmonid waters. Empirical evidence was provided of how current climate change threatens some of the most healthy native brown trout populations in Southern Europe and how forthcoming climate change is expected to further decrease the conservation status of the species.

Ayllón D, Almodóvar A, Nicola GG, Elvira B. Ontogenetic and spatial variations in brown trout habitat selection.
Ecology of Freshwater Fish 2010: 19: 420–432. © 2010 John Wiley & Sons A/S Abstract –  Habitat quality and quantity determine many biological processes and traits that directly affect the population dynamics of stream fishes. Understanding how habitat selection is adjusted to different ecological conditions is essential to improve predictive modelling of population dynamics. We describe brown trout Salmo trutta summer habitat selection patterns through univariate and multivariate habitat selection functions across defined river reach typologies. We sampled 44 sites and performed a principal component analysis that defined eight reach types differing in both local site and catchment‐scale physical features. We observed ontogenetic changes in habitat selection, as trout preferred deeper and slower flowing water as they increased in size. Likewise, selectivity for different types of structural habitat elements changed through ontogeny. Both patterns were consistent across reach types. Moreover, we detected spatial variations in habitat selection patterns within age‐classes among different reach types. Our results indicate that brown trout is a habitat generalist and suggest that spatial variations in habitat selection patterns are driven by physical and environmental factors operating at multiple spatial scales.

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