Josef Matěna

The role of ecotones as feeding grounds for fish fry in a Bohemian water supply reservoir

The food composition of young-of-the-year (YOY) roach, common bream and perch, the dominant fish species in Římov reservoir, was investigated during 1989 and 1990. The littoral fry assemblages were dominated by roach and perch, while bream larvae migrated into deeper water early in their development. The YOY roach fed opportunistically. Up to 15 mm length they remained close to the shoreline, preferring periphyton, Chydoridae and larval Chironomidae. Perch larvae between 10–15 mm long gradually became demersal but their diet continued to consist of the planktonic Cyclops spp. and Diaptomus spp. Resource partitioning was a characteristic feature of the littoral fry assemblages. The only significant overlap in diet occurred with Polyphemus pediculus, which was positively selected by both roach and perch fry.

Littoral age 0+ fish distribution in relation to multi-scale spatial heterogeneity of a deep-valley reservoir

Littoral age 0+ fish were studied with respect to spatio-temporal heterogeneity in the deep-valley Římov Reservoir (Czech Republic) from June to October 2007 using point abundance sampling by electrofishing. The abundance and diversity of age 0+ fish in different types of littoral habitats were examined along the longitudinal gradient of the reservoir during daytime. The impact of some physical attributes of the studied littoral habitats, e.g. slope steepness and substrate size, along with the season was the main factors affecting the distribution of age 0+ fish. The level of structural complexity was not a strong determinant, because the overall diversity and structural complexity of the available littoral habitats were relatively too low to have greater impact on the age 0+ fish distribution. The physical factors markedly influenced the spatial segregation between the two most important taxa in the reservoir—percids and cyprinids. Perch was the only representative of age 0+ percids in the littoral zone, which occupied steep-sloped habitats early in the season. In contrast, gently sloped habitats were mainly occupied by cyprinids later in the season. Species diversity was reflected in the occurrence of age 0+ cyprinids, achieving a maximum in gently sloped habitats in October. The effect of the longitudinal gradients on age 0+ fish distribution and diversity was generally far less significant, but was rather decisive during the period of a pronounced longitudinal trophic gradient during the summer season.

Desiccation resistance of chironomid larvae

Resistance to desiccation in larvae of eight species of aquatic, semiaquatic and terrestrial chironomids (Pseudodiamesa branickii, Macropelopia sp, Prodiamesa olivacea, Micropsectra sp., Chironomus riparius, Chironomus dorsalis, Metriocnemus martini and Camptocladius stercorarius) were studied. The larvae were desiccated in exicator at constant conditions (15 °C, 80% RH) and changes in moisture and body water content were recorded. The LD-50 for loss of body water was calculated. The lowest resistance to loss of body water displayed larvae from subfamilies Tanypodinae and Diamesinae Macropelopia sp. and P. branickii. They survived loss of 49.7 and 56.6% of original water content (presented values are LD-50). On the other hand the highest resistance to water loss was found in C. dorsalis. M. martini and C. stercorarius. The larvae of these species may survive loss of 67.4, 76.6 and 84.2% of original water content. Nevertheless the survival time under experimental conditions depends more closely on larval size that on lethal level of water loss. The smaller larvae desiccated faster and perished sooner than large ones despite they tolerate higher loss of body water.

Who Is Who: An Anomalous Predator-Prey Role Exchange between Cyprinids and Perch

Piscivory in cyprinids (Cyprinidae) is extremely rare. Specifically, common bream (Abramis brama) and common carp (Cyprinus carpio) are zooplanktivorous fish in deep lentic waters. Nevertheless, we observed predation by these two cyprinids under natural conditions in the Vír Reservoir, Czech Republic. We conducted diet analysis for cyprinids caught by trawling and gillnets and the large amount of young-of-the-year (YOY) perch (Perca fluviatilis), with sizes of 37–52 mm standard length, were found in their digestive tracts. In 2010, a large amount of YOY perch caused a significant decrease in Daphnia spp. size and abundance in the reservoir. Hence, a food deficit was induced for the cyprinids, apparent also from the poor nutritional condition of common bream which was much worse than the condition of those in similar reservoirs. Common carp and common bream shifted to forced piscivory, and they utilized the YOY perch as an alternative food source. In contrast, smaller species, such as roach (Rutilus rutilus) and bleak (Alburnus alburnus), widely utilized planktonic cyanobacteria. In the following year, YOY perch occurred in significantly lower numbers and conversely, Daphnia spp. size and abundance were significantly higher. The forced piscivory was not observed. Our results indicate a switch to forced piscivory by cyprinids, which was caused by a shortage of their natural food source. Moreover, this phenomenon presents an effective mechanism for reduction in the numbers of YOY perch, ensuring the stability of the ecosystem.

Spatial and temporal changes of benthic macroinvertebrate assemblages in acidified streams in the Bohemian Forest (Czech Republic)

Outflows from two atmospherically acidified lakes in the Bohemian Forest were studied in 2005 and 2007. While Lake Čertovo has been strongly acidified (∼pH 4.6), Lake Laka was only slightly acidified in the past and is recovering now (∼pH 5.2). The water chemistry and macrozoobenthos composition were analysed along longitudinal gradients of both lake outflows to determine the present status of their streams. A certain progression in stream chemistry to more neutral conditions was observed along the longitudinal gradients of both streams. However, a possible recovery of macrozoobenthos was evident only in the Lake Laka outflow, mainly via an increasing number of Ephemeroptera and Trichoptera taxa, and an increasing number of Gammarus fossarum, both along the longitudinal gradient and during the period of study. In contrast, no considerable changes were observed in the macrozoobenthos composition of the Lake Čertovo outflow, presumably because its chemistry was harmful for acidosensitive taxa such as Ephemeroptera and Trichoptera. Plecoptera and Chironomidae were the most numerous groups in this stream. The biological recovery of both streams will depend on further chemical improvement in their catchments as well as on the dispersal ability of benthic organisms.

Towards a better understanding of small scale distribution of littoral age-0 fish in a deep-valley reservoir: day or night surveys?

The effect of diel period and littoral habitats on the distribution of age-0 fish was tested in a deep-valley reservoir using boat-modified point abundance sampling by electrofishing (PASE). Day and night samplings unveiled differences in abundance of age-0 fish while recognizing most of the commonly present age-0 fish species in the littoral zone. Night survey provided better information about the abundance of age-0 fish since most species appeared in higher numbers at night. Alternatively, night sampling underestimated bleak (Alburnus alburnus) and gudgeon (Gobio gobio), which were predominantly found in the littoral zone in the daytime. The structure of the age-0 fish assemblage was determined primarily by the characteristics of the littoral habitats, i.e. slope steepness and structure, and three different patterns of habitat use were detected among the fish species. To obtain the most comprehensive assessment of a littoral age-0 fish assemblage and to register all species-specific patterns of habitat use, it is necessary that all littoral habitats in the reservoir are sampled during both day and night periods. The boat-modified PASE could be also used as a standard monitoring tool for routine age-0 fish sampling under difficult conditions of steep-sloped shorelines in large inland waterbodies.

Recovery of brown trout populations in streams exposed to atmospheric acidification in the Bohemian Forest

Abstract. Water chemistry and fish occurrence in outflows from two lakes recovering from acidification were studied during 2005–2010. The two lakes represented the regional extremes: while Lake Laka (LA) was the least acidified among the Bohemian Forest lakes, Lake Čertovo (CT) was the most acidified. Water chemistry improved downstream in either outlet due to mixing with less acidic water from tributaries. While pH of the LA stream was circumneutral and concentrations of ionic aluminium (Ali) were low (< 50 μg.l-1) except for temporary acidic episodes during snowmelt, the CT stream remained permanently acidified with Ali concentrations (> 200 μg.l-1) throughout the year and was considered as a reference site. Brown trout (Salmo trutta s.l.) survived in the LA stream already at 0.7 km from the lake. A stable trout population, including young-of-the-year fish increasing in numbers, was found in the LA stream between 2005 and 2010 despite the spring short-term acid episodes. Any recovery of the CT stream is unlikely as the outflow continued to be acidic at 1.5 km from the lake and Ali concentrations were still by one order of magnitude higher than the limit acceptable by trout.

Assessment of burbot Lota lota (L. 1758) population sustainability in central European reservoirs: LOTA LOTA POPULATIONS IN CZECH IMPOUNDMENTS

A novel sampling scheme, using a combination of electrofishing, visual exploration by scuba divers, two types of fyke nets and longlines, was tested in four reservoirs (including their inlets and outlets) to monitor a population of burbot Lota lota. This was supplemented by fry trawling and vertical hydro-acoustics, to detect L. lota larvae in two deep reservoirs that have had a long-term stocking programme. The majority of the L. lota detected were juveniles, captured by electrofishing in the littoral zones of the reservoirs and in running waters. Older individuals were rarely captured with longlines or fyke nets in deeper zones or structured habitats within the reservoirs. A combination of multiple sampling methods provided an assessment of the whole population. Population establishment could not be demonstrated as the age structure of the sampled fish corresponded with that of the stocked fish. Low post-stocking survival, migratory behaviour, interactions with other species and warmer water temperatures are considered the potential drivers for unsuccessful establishment of L. lota populations in these reservoirs.

Condition and feeding behaviour of subadult burbot (Lota lota) in riverine and lacustrine environments

The condition and feeding behaviour of burbot, a widespread potamodromous species in riverine and lacustrine environments, were compared in order to evaluate the importance of both in three artificial systems. Subadult burbot were sampled in three temperate reservoirs in spring, and one of them also in summer and autumn. Standardised abundance and sizes of burbot were comparable between the reservoirs, but the conditions were significantly different. The Clark’s condition coefficient and index of fullness were independent of burbot size and individuals. Feeding behaviour in terms of abundance and composition of consumed food was environment-dependent. The most common prey category was aquatic insect larvae, dominating in the riverine environment. Permanent water invertebrates, microcrustaceans, beetles and crayfish were less common food and eaten more often in the lacustrine environment. Prey-fish were usually the most common species of suitable size. The food analyses demonstrated opportunistic feeding behaviour with selection of prey associated with benthic habitat and suitable size. Burbot is therefore flexible not only in environments utilisation, but also feeding strategy.

Benthic macroinvertebrates along the Czech part of the Labe and lower section of the Vltava rivers from 1996-2005, with a particular focus on rare and alien species

In the Czech part of the Labe River and the lower part of the Vltava River, we examined if the benthic macroinvertebrate composition changed from 1996 to 2005 due to expected improvements in water quality resulting from socioeconomic changes in the Czech Republic since the 1990s. Special attention was given to rare and alien species. The four biological metrics used (Number of taxa, BMWP, Number of sensitive taxa, and Number of EPT taxa) demonstrated that there was indeed an improvement in water quality as well as a slight improvement of the Labe microhabitats during the investigated period. An increasing Number of taxa over time was observed at most sites. Two main concurrent ecological processes are recently in progress in the Labe: a recovery of native species and an expansion of alien species, some of which are considered invasive. The caddisfly Setodes punctatus and the beetle Pomatinus substriatus, considered as regionally extinct in the Czech Republic until 2005, were rediscovered during our investigations. Findings of the crustacean Hemimysis anomala (invasive) and the chironomids Stenochironomus sp. and Lipiniella sp. were the first records of these taxa in the Czech Republic.