Summary Throughout Europe in the last decade there has been a steady shift away from more technical fish pass designs to more nature‐like passes, such as nature‐like bypass channels. Upstream fish passage in a nature‐like bypass channel was investigated in a lowland river, the Lima River, for 117 days from March 2000 to May 2002. Fish passage was recorded using an automatic video recording system. Electrofishing samples within the bypass and below the weir were compared with species abundance found on the tape recordings. More than 7500 individuals of eight species passed through the bypass channel. Species composition was dominated by striped mullet (65.3%) and potamodromous species (34.3%), which used the bypass mainly at night. Of the environmental variables considered, bypass discharge explained most of the variation in the number of cyprinids, whereas water temperature was more important for diadromous species. Comparing species composition below the weir using passage recordings provided a useful tool to assess species efficacy of the bypass, although biological requirements should also be taken into account. This study proved the efficacy of the bypass for passage of almost all occurring species and life stages and also for providing suitable habitat for fish fauna, highlighting the use of these facilities for river restoration schemes.

– Factors associated with the spatial and temporal variation of the lower Guadiana basin (southern Iberia) fish community were determined using data from 20 sites sampled during the summer of 1994 (dry year following a period of low discharge, total discharge from 1992 to 1994=1.45×109 m3) and again during the summer of 1996 (wet year following a period of higher discharge, total discharge from January 1995 to August 1996=6.18×109 m3). From the 17 explanatory variables initially considered six were retained for analysis by a forward selection procedure: maximum depth, altitude, channel width, substrate coarseness, SALT (a dummy variable identifying sampling locations belonging to tributaries that discharge to the brackish Guadiana) and YEAR (a dummy variable identifying the sampling year). Further, we partitioned the total variability in the Guadiana fish community into that accounted uniquely by selected environmental variables (34.9%), uniquely by sampling year (4.1%), by both sampling year and environmental variables (0.3%), and unexplained (60.7%).NOTE

Microhabitat use by Iberian nase Chondrostoma polylepis and Iberian chub Squalius carolitertii in three small streams, north-west Portugal Un resumen en españ ol se incluye detrás del texto principal de este articulo.Abstract -Microhabitat use of Iberian nase Chondrostoma polylepis (Steindachner 1865) and Iberian chub Squalius carolitertii (Doadrio 1988) was studied in three small streams of the Lima basin, north-west Portugal. Measurements were made for 210 and 248 individuals, respectively, distributed in two size classes, based on fish ages, during winter, spring, summer and autumn 1998. Both species moved to shallow and slowflowing microhabitats in summer and autumn, but this mainly reflected seasonal variation in microhabitat availability. Larger individuals of both species used deeper and lower percentage cover areas than smaller conspecifics, however significant ontogenetic differences were only found for water velocity. Different patterns of nonrandom microhabitat use were displayed by both cyprinids. Larger I. nase were in deeper and more discovered waters than those available in the habitat, whereas I. chub was over-represented in slow-flowing areas. There was no evidence of interspecific competition for microhabitat, therefore it is unlikely that spatial resource was limited during the present study.

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From March 1998 to February 1999, upstream fish passage was continuously monitored by video tape analysis at the fish lift Touvedo Dam on the Lima River, northern Portugal. A total of 1194 individuals from seven species were transferred by the lift. Cyprinids were the dominant group collected, with Iberian nase Chondrostoma polylepis (Steindachner) (31.8%) being the most abundant species, followed by Iberian barbel Barbus bocagei (Steindachner) (21.1%), Iberian dace Leuciscus carolitertii (Doadrio) (19.2%) and Iberian red roach Rutilus arcasii (Steindachner) (7.1%). Brown trout Salmo trutta fario (L.) and European eel Anguilla anguilla (L.) accounted for 10.8%, whereas Atlantic salmon Salmo salar (L.) was rarely observed. Most cyprinid seasonal movements were observed in the spring and were associated with reproduction. The timing of the run varied and its beginning appeared to be mainly dependent on water temperature. Roach, dace and nase used the fish lift intensively from mid‐April until the end of summer. Barbel use of the lift intensified in mid‐May in association with warmer water. Salmonids migrated in June–July and autumn. Significant differences were not found in hourly activity, except for nase and barbel, in June and July, respectively. Fish passage was not related to river discharge. The relative effectiveness of the fish lift is discussed in relation to the various species.