The effect of rising seawater temperature on growth of 0-group sole Solea solea and plaice Pleuronectes platessa in the southeastern North Sea was investigated for the period 1970 to 2004 using annual autumn pre-recruit survey data and frequent surveys on a nursery ground. Autumn length showed an increasing trend in sole but not in plaice. Increasing winter temperatures significantly increased the growing period of sole, a warm-water species that spawns in spring, but not of plaice, a temperate species that spawns in winter. Growth rate increased with higher summer temperatures in sole and to a lesser degree in plaice. Compared to experimental growth rates at ambient temperatures and unlimited food, observed growth rates were close to experimental values until mid-June but were much lower in July to September, suggesting food limitation in summer. The higher temperatures observed since 1989 positively affected the quality of the shallow coastal waters as a nursery area for sole but not for plaice. A further increase may negatively affect the nursery quality if the production rate of benthic food cannot meet the increase in energy requirements of 0-group flatfish.KEY WORDS: Climate change · Temperature · Growth · Food limitation · Juvenile · Sole · Solea solea · Plaice · Pleuronectes platessa · Spawning time · North Sea 358: 219-230, 2008 production coincided with an increased input of nitrates and phosphates in the 1960s and 1970s (Beukema & Cadée 1988, Colijn et al. 2002. It is expected that productivity in this area has decreased since the mid-1980s in response to the reduction in nutrient input (Boddeke & Hagel 1995, Lenhart 2001, but this is still under debate (Cadée & Hegeman 2002, Philippart et al. 2007). Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerThe coastal waters of the southeastern North Sea are important nursery grounds for juvenile flatfish like sole Solea solea and plaice Pleuronectes platessa (Zijlstra 1972, van Beek et al. 1989. Detailed studies suggest that growth of 0-group flatfish is determined by ambient temperature conditions and not by food conditions (van der Veer & Witte 1993), as has been reported for sole (Pihl 1989, Rogers 1994, van der Veer et al. 2001, Amara 2003, plaice (Zijlstra et al. 1982, van der Veer & Witte 1993, Amara 2003 and flounder (Pihl 1989, van der Veer et al. 1991. Only a few studies provided evidence for reduced growth in plaice (Nash et al. 1994), either through intra-specific competition (Rijnsdorp & van Leeuwen 1992, Modin & Pihl 1994 or through changes in the abundance or quality of food (Berghahn et al. 1995). On a large spatial scale, however, indirect support for the role of food quality and/or quantity is provided by the observed increase in growth of juvenile plaice and sole in the 1960s and 1970s (Rijnsdorp & van Leeuwen 1992, Millner & Whiting 1996, which could be related to the eutrophication of the coastal waters and the observed increase in benthic biomass (Reise 1982, Beukema & Cadée 198...

1. Large river floodplains are considered key nursery habitats for many species of riverine fish. The lower Volga River floodplains (Russian Federation) are still relatively undisturbed, serving as a suitable model for studying the influence of flooding and temperature on fish recruitment in floodplain rivers. 2. We examined the interannual variability in recruitment success of young-of-the-year (YOY) fish in the lower Volga floodplain in relation to flood pulse characteristics and rising water temperatures in the spring. We sampled four areas with different flooding regimes, in three consecutive years (2006)(2007)(2008). 3. Extensive areas with a long duration of flooding accommodated high densities of young fish. This suggests that extended inundation improves the recruitment success of river fish. In areas with extensive flooding, the biomass of YOY of most fish species was about three times higher in 2006 and 2007 than in 2008. We hypothesise that low spring temperatures in 2008 may have caused this reduced recruitment and that a flood synchronised with rising temperature enhances recruitment success. 4. Extensive flooding was particularly favourable for species characterised by large body size, delayed maturation, high fecundity and low parental investment, such as pike Esox lucius, roach Rutilus rutilus and ide Leuciscus idus. Gibel carp Carassius gibelio, a species tolerant of high temperature and hypoxia, did particularly well in small waterbodies in the driest parts of the floodplain. 5. Structural characteristics of floodplain waterbodies explained much of YOY fish density. These species-environment associations varied from year to year, but some species such as common bream Abramis brama, roach and gibel carp showed consistent relationships with structural habitat characteristics in all years, despite large interannual fluctuations in flood pulse and spring temperature.

The objective was to develop spatially based (type-specific) methods to assess the ecological status of European rivers according to the EU Water Framework Directive. Some 15 000 samples from about 8000 sites were pre-classified within a five-tiered classification system based on hydromorphological and physico-chemical pressures. The pre-classification was used to identify reference conditions and to calibrate the assessment methods. Clustering reference sites based on relative species composition resulted in 60 fish assemblage types within 11 of the ecoregions under study. Discriminant function analyses (DFAs) were employed to identify environmental parameters characterising fish assemblage types; altitude, river slope, wetted width, mean air temperature and distance from source were the principal predictors. These environmental parameters were used to assign impacted sites with altered fish assemblage composition to the reference fish assemblage type. Metrics (fish assemblage descriptors) responding to human pressures were selected based on correlation and DFAs. Assessment methods were developed for 43 fish assemblage types. Metrics based on individual sentinel species were more often used in type-specific methods than metrics related to reproduction, habitat and feeding. Metrics based on long-distance migrants and potamodromous species were more sensitive to human pressures than overall composition metrics, e.g. total number of species. Only some of the tested metrics showed pressure-specific responses, i.e. reacted to one type of pressure but not to others. Insectivorous, intolerant and lithophilic species exclusively responded (decreased) to chemical and hydromorphological pressures in 14-19%. Omnivorous species was the only metric type that showed a consistent reaction (increase) to continuum disruptions in 25% of the cases. Accuracy of methods based on cross-validation with pre-classification varied between 47% and 98% (mean 81%) when contrasting calibration data set (class 1 and 2) with degraded sites (class 3, 4 and 5).

Large European floodplain rivers have a great diversity in habitats and fish fauna, but tend to be heavily modified. The complexity of these river systems and their multiple human impacts pose considerable challenges for assessment of their ecological status. This paper discusses: (1) the application of historical information on fish fauna and habitat availability to describe reference conditions; (2) responses of fish assemblages to human disturbance by comparing various rivers and river segments with different impacts and/or time series within rivers; (3) the role of floodplain water bodies in ecological assessment; and (4) monitoring of large rivers using different gears and sampling designs for main channels and floodplain habitats. The challenge for the future is to standardise and calibrate sampling methods and data to enhance the potential for ecological assessment of large rivers.

Large-scale migratory patterns of adult rheophilic fish [barbel, Barbus barbus (L.), chub, Leuciscus cephalus (L.), ide, Leuciscus idus (L.), nase, Chondrostoma nasus (L.)] were studied in relation to habitat quality and possible migration barriers in the lower rivers Meuse and Rhine, the Netherlands, using a telemetry system with transponders and detection stations based on inductive coupling. Most fish moved over short distances (<10 km), especially those residing in river stretches with high habitat diversity year-round. About 16% of fish used river stretches over 50 km and two ide moved more than 200 km along free-flowing river stretches. One-third of barbel, chub and nase from a Weir-regulated river stretch moved upstream during the spawning season to spawning habitats. Some fish resided in the areas immediately downstream of weirs and fishways during the spawning season, although it was unclear to what extent these observations reflected habitat choice or barriers to migration.K E Y W O R D S : barrier, cyprinid, fishway, habitat, migration, telemetry.