Javier Oscoz

River channelization effects on fish population structure in the Larraun river (Northern Spain)

As a consequence of the construction of the A-15 highway between 1991 and 1995, some modifications affecting the Larraun River (Navarra, North of Spain) were made. One of the most important effects was the channelization of a section of the river in the middle zone. Fish were caught by electrofishing in August of 1996 in the channelized reach, as well as in non-modified stretches upstream and downstream. Physical and chemical variables and shelter availability were also analyzed. The captured fish were measured (total length) and released into the river. We calculated the density, biomass, length distribution and diversity, comparing the obtained results from the different stretches. The number of species was higher in the lower zones of the river and diversity increased progressively downstream. The fish density in the channelized section was slightly lower than in the other two points. Also biomass in the channelized section was about a factor of 10 smaller than the calculated biomass in unaltered points. Moreover, in comparison with the unaltered sections of the river, in the channelized area a major decrease in the presence of fish larger than 150 mm was detected. The low shelter availability in the channelized section, lack of bank vegetation and alterations in the substratum could explain the observed variations in the length distribution, biomass and the lower value of the density of European minnow, Phoxinus phoxinus (Linnaeus, 1758).

An alien ectosymbiotic branchiobdellidan (Annelida: Clitellata) adopting exotic crayfish: a biological co-invasion with unpredictable consequences

Abstract Invasive alien species present a global threat to biodiversity, particularly where pathogens and symbionts are involved. Branchiobdellidans are clitellate annelids with an obligate ectosymbiotic association primarily on astacoidean crayfish. There are several examples of branchiobdellidan species adopting a geographically exotic host where endemic and exotic crayfishes cohabit the same water body. The first records of a western North American branchiobdellidan, Xironogiton victoriensis, adopting the eastern North American crayfish, Procambarus clarkii, in 2 river basins in Spain provide further evidence of the ectosymbionts’ tolerance to adopt an exotic host. Given worldwide translocations of these and other commercial crayfish species, limnologists and agency managers need to be alert for further introductions of X. victoriensis and other branchiobdellidans. Impacts of these exotic ectosymbionts on habitat and biota at a new location are unknown, as are their consequences on native biodiversity.

Invading the invaders: relationships of an exotic branchiobdellidan with its exotic host and environmental conditions

Abstract Environmental conditions and host features that influence the abundance of an exotic branchiobdellidan were studied. One of the most widespread invasive crayfish species in Europe is the signal crayfish, Pacifastacus leniusculus (Dana, 1825). Along with this invasive crayfish, other alien species that live on the crayfish’s body surface, such as bacteria, algae, fungi and invertebrates, were introduced. One of these symbiont species is a branchiobdellidan worm, Xironogiton victoriensis (Gelder and Hall, 1990). Because a previous study identified this exotic branchiobdellidan in 3 different and spatially separate populations of the red swamp crayfish, Procambarus clarkii (Girard, 1852), an investi-gation into the factors affecting its abundance was necessary. We sampled 1817 sites between 2005 and 2013 in the Ebro Basin (Spain), and the distributions of X. victoriensis and P. leniusculus were represented and interpreted. Furthermore, we sampled 2914 crayfish from 43 Spanish localities to investigate the influence of environmental conditions and host features (sex, body size, body condition, density and ecdysis) on the abundance of X. victoriensis. The abundance of the branchiobdellidan was higher in the largest individuals and in those showing the best body condition. The crayfish body condition (or welfare) increased significantly with the branchiobdellidan infestation, suggesting that mutualism is the biological relationship between X. victoriensis and P. leniusculus. Although 91.04% of the adult signal crayfish were infested with X. victoriensis, only 59.3% of the juveniles were infested. Nonmolted crayfish had higher branchiobdellidan abundance than that of recently molted host specimens; however, the abundance of the symbiont did not differ between sexes and host densities. Finally, biochemical oxygen demand, phosphates, coliforms, and potassium were positively related with the branchiobdellidan abundance. The relationships between some environmental variables and the abundance of branchiobdellidans have not been previously well studied, and these findings will be important for risk assessments and models predicting the spread of exotic branchiobdellidans.

Threatened fishes of the world: Barbus haasi (Mertens 1925) (Cyprinidae)

barbel not reaching the rear edge of the eye. Last unbranched ray of the dorsal fin with small denticles. Anal fin is long and caudal peduncle is short and high. Body presents dark blotches. Part of caudal, anal and pelvic fins are red. Drawing by Rafael Miranda. Distribution: Most headwater streams of the Ebro River Basin and North Mediterranean rivers of the Iberian Peninsula. Abundance: Restricted to headwaters and occasionally in middle reaches of streams, scarce where present. Habitat and ecology: This benthonic species prefers upper reaches of rivers, with high flow and clear, cold waters. Barbus haasi occurs in rocky and vegetated areas and feeds on macroinvertebrates (mainly Chironomidae, Ephemeroptera and Trichoptera). Reproduction: The spawning period extends throughout April and June, related to periods of high stream flow. Fecundity ranges from 2000 to 7000 eggs per female. The males have an early maturity (one year) and grow more slowly than females. The females live for 8 years while the males only live for 7 years. The females have multiple spawning, releasing two to five egg batches depending on their size, such that largest females spawn more batches than the small ones (Aparicio & Sostoa 1998). Threats: The species is threatened by invasive alien fish species (mainly piscivores) and habitat loss due to water abstraction, construction of small dams, stream desiccation, etc. Anthropogenic water pollution is another important disturbance factor. This endemic species of the Iberian Peninsula is currently in rapid decline because the above noted impacts are intensified by the characteristic irregularity of the Mediterranean rivers. Conservation action: None. Conservation recommendations: Waste water and water pollution control and treatment. Correction of the impact of stream regulation by water releases to simulate natural flow patterns. Prevent alien fish species introductions and eradication of the existing alien species which impact on B. haasi. Habitat protection and control of invasive alien fish species are the main actions necessary to prevent the further decline of Barbus haasi. Remarks: There has been some controversy with regard to the systematic position of

Why, Where and How: An Identification Guide of Macroinvertebrates

This chapter provides a general introduction to the identification of macroinvertebrates, with particular emphasis on the management of river systems and the correct identification of these animals in field surveys. Subsequently, the study area and taxonomic groups considered are defined and delimited. Technical considerations about photographic methods are also included at the end of the chapter.

Environmental factors influencing the distribution and abundance of the introduced signal crayfish in the north of Iberian Peninsula

The identification of habitat requirements of invasive species is essential to evaluate their spread and to assess the vulnerability of recipient ecosystems. We studied the distribution and abundance of the invasive signal crayfish (Pacifastacus leniusculus) in 43 sites in northern Spain and analysed the relationships with several abiotic and biotic parameters of the aquatic ecosystems. Our results indicated that the abundance of signal crayfish was positively associated with vegetation cover and negatively associated with boulders. Also, its abundance was positively correlated with water temperature, organic matter, cations (e.g. sodium), anions (e.g. sulfates) and abundance of some native fish species (Parachondrostoma miegii and Luciobarbus graellsii). We concluded that the habitat of signal crayfish is among salmonid stretches (headwaters) with cold waters and low proportion of organic debris, and among cyprinid stretches (low waters) with warmer waters which it inhabits with another invasive crayfish, the red swamp crayfish (Procambarus clarkii). Our analysis indicated that the presence of signal crayfish is limited in the uppermost stretches by lower water temperatures and a lower proportion of organic debris. The existence of a natural environmental limiting factor in upstream reaches facilitates the conservation of aquatic ecosystems and native fauna.

Taxa Description and Biology

This section of the book includes brief morphological and anatomical descriptions of the studied taxa. Data on the biology of the families is also provided, partly for completeness but also to allow the reader to gain a better understanding of these animals. The list of authors for each taxon is included in the front matter of this book.