Benigno Elvira

Life-history traits of non-native fishes in Iberian watersheds across several invasion stages: a first approach

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.

Conservation status of endemic freshwater fish in Spain

Abstract The present conservation status of the endemic freshwater fish of Spain is reviewed and compared with a former list made in 1986. Ten taxa (species and subspecies) are exclusively endemic to Spanish waters, 13 are Iberian endemics (Spain and Portugal), while three other species are also found in neighbouring European (France and Italy) or African (Algeria) countries. Endemic species belong to the families Clupeidae (33% of the native taxa), Cyprinidae (87%), Cobitidae (100%) and Cyprinodontidae (100%). A greater part of the endemic fish fauna is threatened, since three taxa are endangered, five vulnerable, seven rare and two insufficiently known.

Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins

Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes and variability of flow regimes.

Latitudinal and altitudinal growth patterns of brown trout Salmo trutta at different spatial scales.

Spatial variation in growth of stream-dwelling brown trout Salmo trutta was explored in 13 populations using a long-term study (1993-2004) in the Bay of Biscay drainage, northern Spain. The high variability in fork length (L(F)) of S. trutta in the study area was similar to the body-size range found in the entire European distribution of the species. Mean L(F) at age varied: 0+ years, 57.4-100.7 mm; 1+ years, 111.6-176.0 mm; 2+ years, 155.6-248.4 mm and 3+ years, 194.3-290.9 mm. Average L(F) at age was higher in main courses and lower reaches compared with small tributaries and upper reaches. Annual specific growth rates (G(L)) were: 0+ to 1+ years, 0.634-0.825 mm mm(-1) year(-1); 1+ to 2+ years, 0.243-0.342 mm mm(-1) year(-1); 2+ to 3+ years, 0.166-0.222 mm mm(-1) year(-1), showing a great homogeneity. Regression models showed that water temperature and altitude were the major determinants of L(F) at age variability within the study area. A broader spatial analysis using available data from stream-dwelling S. trutta populations throughout Europe indicated a negative relationship between latitude and L(F) of individuals and a negative interaction between latitude and altitude. These findings support previous evidence of the pervasive role of water temperature on the L(F) of this species. Altitude appeared as the overall factor that includes the local variation of other variables, such as water temperature or food availability. At a larger scale, latitude was the factor that encompassed these environmental gradients and explained the differences in L(F) of S. trutta. In summary, L(F) at age in stream-dwelling S. trutta decreases with latitude in Europe, the converse of Bergmanns rule.

Spatial Variation in Brown Trout Production: The Role of Environmental Factors

Abstract Spatial variation in Spanish populations of brown trout Salmo trutta was studied in 10 streams of contrasting environmental and biological characteristics based on data compiled over 7 years (1992–1998). Three of the streams had soft water (mean alkalinity as CaCO3 = 19.3 mg/L) supplied by granite catchments at elevations around 1,250 m above sea level and had a low abundance of macroinvertebrates (mean density = 598 individuals/m2; mean biomass = 0.63 g/m2). The remaining streams had hard water (mean alkalinity = 253.6 mg/L) flowing over limestone at 850–1,400-m elevations and possessed a greater benthic faunal abundance (mean density = 2,433 individuals/m2; mean biomass = 2.76 g/m2). Mean brown trout population characters varied significantly throughout the study area (density = 1,567–5,594 fish/ha; biomass = 56.6–240.2 kg/ha; annual production = 47.0–182.0 kg/ha, and the ratio of annual production to mean biomass = 1.01–1.56). A stepwise multiple regression analysis revealed a significant rela...

Effects of environmental factors and predation on benthic communities in headwater streams

Structure and composition of benthic macroinvertebrate assemblages were investigated during three consecutive years in six headwater streams that exhibit a high variation in environmental conditions, habitat structure and predatory pressure. We examined whether the abundance of functional feeding groups could be best predicted by the abundance of predators and some habitat and chemical variables. Mean density and biomass of macroinvertebrate functional feeding groups varied significantly throughout the study area. Stepwise multiple regression analyses revealed that both density and biomass of functional feeding groups was influenced primarily by chemical features of water. Shredder biomass and scraper density were also influenced by habitat features, the abundance of scrapers increasing in deeper localities at lower altitudes and with abundant macrophytes. The abundance of predatory invertebrates was related to the density and biomass of benthic prey. An influence of fish predation on invertebrate communities was not observed in the study streams. The finding that benthic communities in undisturbed headwater streams are mainly affected by water chemistry variables irrespective of fish predation and habitat features clearly highlight the sensitivity of functional feeding groups to changes in chemical features and their role as indicators for bioassessment.

Thermal Carrying Capacity for a Thermally-Sensitive Species at the Warmest Edge of Its Range

Anthropogenic environmental change is causing unprecedented rates of population extirpation and altering the setting of range limits for many species. Significant population declines may occur however before any reduction in range is observed. Determining and modelling the factors driving population size and trends is consequently critical to predict trajectories of change and future extinction risk. We tracked during 12 years 51 populations of a cold-water fish species (brown trout Salmo trutta) living along a temperature gradient at the warmest thermal edge of its range. We developed a carrying capacity model in which maximum population size is limited by physical habitat conditions and regulated through territoriality. We first tested whether population numbers were driven by carrying capacity dynamics and then targeted on establishing (1) the temperature thresholds beyond which population numbers switch from being physical habitat- to temperature-limited; and (2) the rate at which carrying capacity declines with temperature within limiting thermal ranges. Carrying capacity along with emergent density-dependent responses explained up to 76% of spatio-temporal density variability of juveniles and adults but only 50% of young-of-the-years. By contrast, young-of-the-year trout were highly sensitive to thermal conditions, their performance declining with temperature at a higher rate than older life stages, and disruptions being triggered at lower temperature thresholds. Results suggest that limiting temperature effects were progressively stronger with increasing anthropogenic disturbance. There was however a critical threshold, matching the incipient thermal limit for survival, beyond which realized density was always below potential numbers irrespective of disturbance intensity. We additionally found a lower threshold, matching the thermal limit for feeding, beyond which even unaltered populations declined. We predict that most of our study populations may become extinct by 2100, depicting the gloomy fate of thermally-sensitive species occurring at thermal range margins under limited potential for adaptation and dispersal.

Threatened fishes of the world: Chondrostoma arrigonis (Steindachner, 1866) (Cyprinidae)

Common name: Loina (Spanish). Júcar Nase (English). Conservation status: Endangered (EN A1ae B1+2bcde, Spanish Red Data book, Doadrio 2002). Critically Endangered (CR A2ace; B2ab (i, ii, iii, iv, v), Crivelli 2005, Smith and Darwall 2006). Identification: D III + (7)8, A III + 8–10, V II + 8, P I + 14–15, pharyngeal teeth 6–5 or 5–5, LL 44–53, gill rakers 16–23. Reaches 250 mm TL. A slender-bodied fish, compressed from side to side. The head is small with the mouth ventral. From below the mouth is arched; the upper lip is soft and fleshy, but the lower lip has a thin horny layer. The outline of the dorsal fin is straight or slightly concave, that of the anal fin is slightly concave. Drawing by F. Steindachner. Distribution: C. arrigonis is restricted to the Júcar river basin in eastern Spain (Elvira 1980). Abundance: It was a rather common species in the past all over its distribution range. Nevertheless, a field study carried out at 30 sites in the Júcar basin in 2001 found only 21 specimens at three sites, and in 2004 found only 10 specimens at one of the three sites. The known current range of the species only includes ten sites at three river Júcar tributaries: rivers Cabriel (five sites), Magro (four sites) and Sellent (one site) (after the field work of 2005 made by the Valencian Community authorities). Habitat and ecology: C. arrigonis is a rheophilic, schooling fish which lives in all river sections, but mainly in the middle reaches. Reproduction: Spawning takes place in gravel beds from March to May, after an upstream migration by the adults. Threats: The species is threatened by pollution and excessive water extraction, and by the introduction of exotic fishes. Some major predators, such as Pike Esox lucius L., 1758, Largemouth Bass Micropterus salmoides (Lacépède, 1802) and Zander Sander lucioperca (L., 1758) are currently widespread in the Júcar river basin (Elvira and Almodóvar 2001). The water transfer system Tagus-Segura has allowed a close and neighbouring species, the Tagus Nase Chondrostoma polylepis Steindachner, 1865, to enter the Júcar basin, compete and B. Elvira (&) A. Almodóvar Department of Zoology and Physical Anthropology, Faculty of Biology, Complutense University of Madrid, E-28040 Madrid, Spain e-mail: belvira@bio.ucm.es

Cytotaxonomy of Iberian loaches with some remarks on the karyological evolution of both families (Pisces, Cobitidae, Homalopteridae)

SUMMARYThe three species of cobitoids inhabiting the Iberian Peninsula were cytogenetically analysed—Cobitis calderoni, C. maroccana and Nemacheilus barbatulus. Metaphasic plates of specimens collected in several Portuguese and Spanish streams and, for the stoneloach, also in a central European river, were compared. All the species have a diploid value of 2n = 50 and are characterized by a high incidence of chromosomes with terminal/subterminal centromeres, particularly the cobitids. In spite of their phenotypical distinction, the spined-loaches karyotypes are grossly similar, suggesting only the occurrence of punctual chromosome rearrangements related to the respective differentiation processes. The lack of well-apparent interpopulation chromosome variability and the existence of diploid-polyploid relationships in these Euro-Asiatic families is finally discussed according to the new model of Cyprinidae karyological evolution.

Current occurrence of the Atlantic sturgeon Acipenser oxyrinchus in northern Spain: A new prospect for sturgeon conservation in western Europe

Acipenser oxyrinchus is considered extirpated in Europe, but numerous breeding populations still exist on the Atlantic coast of North America. An adult female A. oxyrinchus, 2500 mm total length and 120 kg wet weight, was accidentally fished on 24 November 2010 near the coast of Gijón, Asturias, Spain. The fish was identified by its morphological pattern as well as by mitochondrial and nuclear DNA analyses. Because the sturgeon was found far away from any known breeding area, it was considered a stray or vagrant specimen. It certainly has a natural origin, but its eventual birthplace could not be determined. Because its current occurrence was unknown in southwestern Europe until now, the species is not cataloged or protected in this area. Therefore, the residual European stocks of A. oxyrinchus ought to be listed as Critically Endangered (CR) according to the IUCN categories. Likewise, it is imperative for southwestern European countries with an historic or recent occurrence of A. oxyrinchus to protect the species through domestic and international legislation. The present sympatric occurrence of A. sturio and A. oxyrinchus raises new challenges about key questions, such as the species selection for restoration program in European countries. Accurate monitoring is mandatory to obtain appropriate information for an assessment of the current occurrence of A. oxyrinchus in southwestern Europe.