Young-of-the-year fish assemblages as an alternative to adult fish monitoring for ecological quality evaluation of running waters

Abstract

The EU's Water Framework Directive (WFD) in particular makes good use of riverine biota-including fish-as ecological indicators of river integrity. However, it is also important to examine when our indicators fail to serve the purpose for which they were originally intended: to consistently and reliably describe the quality of the environment. We argue that in the Czech Republic (and probably several other European countries), the use of adult fish as ecological indicators often fails to fulfill these purposes for several reasons, especially when fish are stocked in natural waters, for practical considerations during field sampling, and problems with public relations. The ecological quality of running waters sensu WFD is usually assessed on the basis of the adult fish assemblage. The aim of this study is to describe disadvantages of monitoring river integrity using adult fish in Czech Republic, which has regular and widespread stocking of more than one-third of fish species present in running waters and to suggest the alternative strategy of young-of-theyear (YOY) fish monitoring for assessing river ecological quality with the ability to provide a sensitive response to water quality and habitat structure regardless of the effect of stocking or river size. We conclude that even though YOY sampling is often a more logical and practical approach to water quality monitoring under specific conditions, no method is perfect and caution should be taken. For example, YOY can have high annual variability in density and higher sensitivity to summer flood events than adults. The suitable time for sampling YOY fishes in late summer is much shorter than for the adult fish community, and therefore must be considered when designing a successful monitoring strategy. Monitoring of YOY fishes does not provide direct information about age structure of fish populations, which is required by WFD. YOY sampling is a useful-albeit imperfect-method for providing a sensitive response to ecological status of rivers, especially under specific stocking conditions.

The role of host specificity in explaining the invasion success of the freshwater mussel Anodonta woodiana in Europe

“…A standardised electrofishing method was used to obtain fish data (Jurajda et al 2010(Jurajda et al ) during 2006(Jurajda et al and 2007. Sampling sites were lotic habitats, including upland streams and large lowland rivers, and were evenly distributed throughout the Czech Republic (approximately 78,000 km 2 ).…”

Young-of-the-year fish assemblages as indicators of anthropogenic disturbances in large tributaries of the Seine River Basin (France)

“…species occurrence confirms the sensitivity to water quality (Copp et al, 1991) and the potential indicative value of this particular stage Regression slope (a); intercept of the regression slope (b); mean standardized residuals (D) for the validation dataset (RH74) and for the three different disturbed datasets (CDH74, NDH74, and NCDH74). Values in bold indicate significant differences (Jurajda, 2010), the increase in mean occurrences of B. bjoerkna and L. leuciscus is more surprising. A potential explanation is that water organic pollution can also lead to an increase in river productivity (De Bruyn et al, 2003), favoring particular species according to their biological and functional traits Fig.…”

“…Moreover, using YOY fish assemblages could help to improve or complement the biotic indices previously developed for adult fish assemblages since these indices suffer some important limitations: (1) a poor ability to establish cause-effect relationships (Roche et al, 2005), mostly because of the relatively long time response of adult populations to disturbances (Jurajda et al, 2010); (2) problems in sampling efficiencies for adult fishes in large rivers (De Leeuw et al, 2007); (3) problems linked to fish stocking (Schmutz et al, 2000); and (4) weak efficiency in evaluating river rehabilitation works which are often done at very small grain (few hundred meters) (Adam et al, 2007;Pander & Geist, 2010).…”

Improved trawling setup for sampling pelagic juvenile fish communities in small inland bodies of water

“…Knowledge of yearly recruitment is very important to the prediction of future fish stocks, and the juvenile community also reflects the adult fish community and indicates the success of the natural reproduction (Jurajda et al 2010). Trawling is a common sampling method for pelagic larvae and early juveniles in lakes and reservoirs (Čech et al 2007(Čech et al , Jůza et al 2012 and in the sea (Methot 1986, Itaya et al 2007, and at night, it has been an effective quantitative method without significant fish avoidance reactions that provided reliable information about pelagic juvenile communities (Jůza andKubečka 2007, Jůza et al 2010).…”