Reproductive ecology and growth of a population of brown trout (Salmo trutta L.) in an aquifer-fed stream of Old Castile (Spain)

In the River Lobos-Ucero and its tributary the River Avión-Milanos (Duero basin, Old Castile, Central Spain), two limestone streams fed by aquifers, the population of brown trout, as compared with the populations of other European streams, shows a high growth rate, high condition coefficients, short life-span and early age at first maturity. Gonad cycle was also studied. Size distributions of unshed eggs exhibit a dynamic activity with a bi-modal distribution from June onwards, spawning occurred in the last days of November. Fecundity (F) can be predicted from trout length (L, mm) according to the equation: F= –646.47+5.6167 · L. Numbers and standing crop of trout range from 18 to 3903 ind. ha^–1 and 3.6 to 452.9 Kg ha^–1, reaching higher values in the sites close to the aquifers. Egg production had values of 22.4 and 18.0 eggs m^–2 in the Rivers Ucero and Avión-Milanos respectively. Some factors suggested as regulators of these demographical characteristics are discussed in the light of recent literature.     

Pattern of movements of adult Barbus haasi in a small Mediterranean stream

Most adult Barbus haasi , at a 1950 m-long site in Vallvidrera creek, were highly sedentary and resided within a home range <20 m (32 m²), while a small group were more mobile. On successive sampling occasions, between 52·3 and 64·9% of fish were recaptured in the same 10-m-long section in which they had previously been captured. Movements over long distances were infrequent, and only 5·6% of the fish moved >100 m. The movement pattern of the population was seasonally stable, although the mean distances were slightly greater in summer because of the medium-range movements of a few individuals. Overall, upstream and downstream movements were equally common but a significant downstream movement occurred in spring. The size of the fish did not influence the movement rate. Fish inhabiting those sections of the stream with greater depth, slower current and more cover had a lower movement rate than fish occupying shallower, exposed sections. The restricted movement of B. haasi could increase the survival of fish by increasing the probability of staying in the remaining pools during summer dry-out, and may therefore be of adaptive significance.     

Influence of environment upon the life history of gudgeon, Gobio gobio (L.): a recent and successful colonizer of the Iberian Peninsula

The growth and the reproductive tactics of gudgeon, Gobio gobio (L.) were assessed in three contrasting streams of the Iberian Peninsula: the Rivers Moros and Ucero, tributaries of the R. Duero, and the R. MatarrańGa, a tributary of the R. Ebro. The R. Duero gudgeon have spread in the last 50 years while their presence in the lower tributaries of the R. Ebro followed the construction of reservoirs in the mid 1960s. The life histories of the Moros and MatarrańnGa gudgeon are very similar; rapid growth in spring, early reproduction (1 -year-old), high reproductive cost, short life-span and trend to semelparity. Both populations are strongly influenced by the severe summer droughts that result in (I) reduction in the condition coefficient, (2) reduction in the growth rate (particularly in the River MatarrańGa), (3) single spawning and (4) no gonad development in the summer. The gudgeon in the Ucero delay maturity, grow slower, are multi-spawners and have a longer life span. All the Duero populations come from the same genetic pool and they are actually connected through the populations living along this river basin, whereas the MatarrańGa population is not genetically linked, we hypothesize that the differences between these populations are environmentally induced.     

Life history traits of Mediterranean brown trout (Salmo trutta complex) in Pyrenean headwater streams

Ichthyological Research - The Mediterranean brown trout (Salmo trutta complex) is native to basins draining to the Western Mediterranean Sea, and natural populations are currently declining in...     

Decline of Native Freshwater Fishes in a Mediterranean Watershed on the Iberian Peninsula: A Quantitative Assessment

We examined changes in the distribution of 9 native and 18 introduced freshwater fishes in the south-eastern Pyrenees watershed, Iberian Peninsula, using data from 1996, 1984–1988 and historical information. This region suffers many modifications to its freshwater ecosystems that are linked to human activity in the Mediterranean regions. Fish communities, stream physical habitat and environmental degradation were assessed at 168 sites from 11 basins in 1996. Seven native species (78%) showed decline from previous data, one of which became extirpated in the first half of the 20th century. On the other hand, introduced species are expanding. As a consequence, intact native communities are increasingly rare, declining from presence in 22% of river courses in 1984–1988 to 15% in 1996. The most typical community type is a mixture of native and introduced species occupying 30% of river courses. Stream degradation seems to be the main cause of this process because fish communities differed between degraded streams and streams suffering less impact. A principal component analysis showed that water pollution and modifications to the habitat were the two anthropogenic factors that accounted for most changes in the fish community integrity. Habitat alteration, primarily through construction of dams and water diversions, has fragmented habitats and isolated native fish communities in headwater streams. Current protection measures do not offer effective conservation of threatened species and communities. A global conservation and restoration programme from an ecosystem-based approach is essential to reverse the trend affecting native freshwater fishes in this Mediterranean region.     

Microhabitat use in a mediterranean riverine fish assemblage

Summary We examined microhabitat use in Barbus graellsii, Barbus haasi, Chondrostoma toxostoma, Rutilus arcasii, and Salmo gairdneri over a 19 month period in the upper Rio Matarraña, Spain. B. graellsii and Ch. toxostoma exhibited non-random microhabitat use during all seasons and preferentially occupied deep microhabitats with heterogeneous substrates. During the majority of seasons in which they were present, B. haasi and R. arcasii occurred in microhabitats similar to those occupied by B. graellsii and Ch. toxostoma. S. gairdneri was over-represented in high velocity microhabitats with erosional substrates. We did not observe any evidence of interspecific interference competition or avoidance. Substrate composition did not appear to affect microhabitat use outside of its covariation with depth and velocity. Seaonal variation in microhabitat use by B. graellsii, B. haasi and Ch. toxostoma was strongly correlated with seasonal changes in microhabitat availability. S. gairdneri, however, occurred closer to the substrate when average velocities were high. Larger B. graellsii and B. haasi sometimes occupied deeper, higher velocity microhabitats than did smaller specimens. Larger B. graellsii also occasionally occurred farther from shelter than did smaller specimens; the reverse was true for B. haasi. Larger Ch. toxostoma sometimes were found farther from both the substrate and shelter than smaller individuals, whereas smaller specimens occasionally inhabited deeper areas with more depositional substrates than did larger Ch. toxostoma. During Late Summer 1985, smaller Ch. toxostoma also occupied microhabitats with higher velocities than did larger specimens. A comparison of microhabitat use for two species present in both upper and lower portions of the Matarraña indicated that most differences in microhabitat use could be attributed to inter-site differences in microhabitat availability. The data suggest, hovever, that both species shifted to more protected microhabitats in the higher velocity site. Assemblage members generally occupied statistically distinguishable microhabitats and could be classified as: 1) high-velocity upper water column (S. gairdneri), 2) low velocity lower water column (B. graellsii, Ch. toxostoma and R. arcasii), and 3) shelter-oriented benthic (B. haasi). The introduction of S. gairdneri during Winter 1984 did not produce microhabitat shifts in any of the native species. Whether or not the native species affected microhabitat use in S. gairdneri is unknown. Interspecific competition for space, however, did not appear to strongly influence microhabitat use among the native species.     

Southern Mexican minnows of the genus Notropis (Actinopterygii, Cyprinidae): genetic variation, phylogenetic relationships and biogeographical implications

Allozyme analyses were performed to determine patterns of genetic variation and phylogenetic relationships within the genus Notropis in southern Mexico. Products of 28 gene loci were resolved in 24 geographic samples belonging to four putative species. These species represent the southern limit of the Cyprinidae in North America. Five loci were found monomorphic and 11 were diagnostic among species when the outgroup, Phoxinus phoxinus, was not taken into account. Four groups were identified, but these do not correspond perfectly to the four nominal species. Notropis sallaei was identified by allozyme analyses being the most basal among southern Mexican Notropis and the most genetically divergent. Notropis imeldae, was also diagnosed on the basis of allozymic variation, however a population sample representing the Balsas drainage was genetically divergent and is considered as an undescribed new species (N. n. sp.). No genetic differences were found between the samples of N. boucardi and N. moralesi. Therefore, we recommend that N. moralesi should be considered as a junior synonym of N. boucardi. A broad geographic sampling strategy was employed across all the distribution range of N. boucardi representing rivers from three different drainages, which cover both Mexican slopes. The slight divergence found among the headwater populations of N. boucardi permitted us to predict a model of paleohydrographic relationships of these three drainages. Two alternative hypotheses are postulated to explain the current distribution pattern of populations of N. boucardi in southern Mexico.     

Life-history traits of the endangered river blenny Salaria fluviatilis (Asso) and their implications for conservation

The life-history characteristics of the river blenny Salaria fluviatilis in a Mediterranean stream in north-east Spain have been studied. The maximum age observed was 4+ years in both sexes, although only age groups 0+ and 1+ years were well represented. For both sexes, growth was rapid between April and June (before the summer drought) and in October. The instantaneous rate of monthly growth (April to October) was positively correlated with water depth. All fish attained sexual maturity during their first year of life. Females spawned multiple times. Spawning occurred mainly from June to August, although older females (2+ years old) began in May. The relationship between fecundity and total length recorded for older females in the spring was not significantly different from that obtained for 1 year-old females in the summer. The mean diameter of ripe oocytes, however, was greater in older females. Larger eggs that were laid during a period of good food supply (spring) might have a higher probability of survival. The results suggest that female fecundity is affected by environmental conditions. The species is characterized by fast growth, early maturity, multiple spawning and limited longevity. This may be a good life-history strategy for small fish species in unstable environments, where adult mortality is high, variable or unpredictable. Some life-history traits of the river blenny suggest that this species might be vulnerable to more severe drought conditions than those associated with the Mediterranean climate.     

Observational evidence of the sensitivity of some fish species to environmental stressors in Mediterranean rivers

We describe a tolerance classification based on the physicochemical parameters of water and habitat quality indices for native and introduced fish species in northeastern Spain. Although fish are widely used as biological indicators, the tolerance categories currently available for Spanish Mediterranean fish species are uncertain or subjective. We sampled 430 sites covering a wide range of river conditions, allowing us to develop tolerance scores based on a quantitative assessment. We used indirect ordination methods to establish stress gradients between the environmental variables compiled during the monitoring surveys carried out from 2002 to 2008. We then drew up a tolerance classification for the most common species in our dataset using weighted average inference models based on the following gradients: water quality and the state of physical habitat. The results were corroborated by multivariate gradient analysis. The fish scores obtained were applied to an independent dataset and a positive correlation was found between assessment protocols. Our results corroborate the use of fish, including exotic fish species, as biological indicators. Our findings may be used in a regional Index of Biotic Integrity and for the use of fish in bioassessment studies based on scores.     

Scaled body‐mass index shows how habitat quality influences the condition of four fish taxa in north‐eastern Spain and provides a novel indicator of ecosystem health

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