FishEcU - Specialists for fisheries surveys of large inland waters

Quantitative and qualitative surveys of the fish stock of large inland waters (LIW; waters with surface areas up to 1000 km2 and depths of up to hundreds of meters) represent some of the most challenging tasks of aquatic ecology. HBI was facing the decision of either abandoning this type of survey or of setting up a strong group capable of such surveys. HBI decided on the latter and FISHECU was set up to:
1. provide fish stock assessment, especially in large lakes and reservoirs
2. explain the role of the fish component within the aquatic food web
3. provide support for undergrad, grad and postdoc students studying fish ecology

Most activities of FISHECU are aimed at providing information on the fish component in complex limnological studies carried out by the HBI on LIW. This includes explaining the role of fish in trophic webs in LIW. It also includes providing background information for enhancing the fish stocks for fisheries, biomanipulation, conservation and other practical needs. FISHECU research targets the patterns of fish distribution, behaviour, feeding activity, abundance and biomass in LIW.

Aside from pure research work for government and grant agencies, FISHECU provides limited contract research work for various clients. In previous years, this contract and consultancy work has provided important stimuli for the methodical and professional growth of our unit and enabled us to collect and preserve extensive expertise for fisheries surveys in LIW.


Simplistic scheme of the sampling effort during complex fish stock assessment in LIW. Individual techniques are explained in following text.

The main areas of expertise available include:

Front picture of a survey vessel Ota Oliva with a transducer holder.Acoustics fish stock estimates. HBI has over 35 years of experience in using acoustic methods for fish stock assessment (Straskraba, 1974). In recent years, our focus has mainly been in horizontal sonar applications, limitations of acoustic surveys (such as effects of noise, sound field, and blind zones), relationships between fish size and acoustic target strength, acoustic detection of fish larvae and juveniles, invertebrates, and fish behaviour. The emphasis is on quantitative surveying of all parts and depths of LIW: surface layers are surveyed horizontally, deeper waters vertically. LIW parts which are not suitable for acoustic sampling (such as littoral and near-bottom blind zone) are sampled by other means (see below). Fishecu hydroacustic studies are performed using Simrad EK 60 echosounder operating on frequencies 38, 120, 200 and 400 kHz, and Didson acoustic camera (Dual frequency IDentification Sonar) for detailed investigations of behaviour and underwater structures. Fishecu staff take also an active part in improving sonar technology, especially in developing Sonar 5 postprocessing software in cooperation with the University of Oslo.

Tributary traps in the upper end of the Římov Reservoir.Trapping. Traps, starting from fry traps up to giant traps covering whole-river discharge, also have a long tradition of use in HBI. Although the selectivity of traps limits their usefulness for general fish stock assessment, they are especially useful for eliminating undesirable fish from LIW (Kubecka, 1992) and for fish migration studies (Hohausova et al., 2003, Hladik & Kubecka, 2003).

Purse seining in the Želivka Reservoir.Seining. Since the early 1980s we have regularly sampled the fish stock of LIW with beach seines up to 200 m long using night inshore migration (Kubecka, 1993). When financial sources are limited, this is the most cost-effective way to obtain a reasonable sample of biodiversity and relative abundance of fish communities. At present we have completed investigations on the efficiency of beach seining for sampling of LIWs (Říha et al., 2008). In open water, we operate a 120 m-long 12 m-deep purse seine made according to the design of Tischler et al. (2000). Sampling using such large purse seine is a demanding exercise but it provides very robust information on midwater fish communities.

Good catch of a smelt in multimesh pelagic gillnets in a Dutch reservoir.Gillnetting. Nordic multimesh gillnets were introduced as a standard sampling tool at HBI in 1998. The advantage of these nets is their suitability for sampling every type of habitat found in LIW with a gear of unified construction. The original Nordic series of mesh sizes (5, 6.5, 8, 10, 12.5, 16, 19.5, 24, 29, 35, 43 and 55 mm) were extended by adding the mesh sizes of 70, 90, 110 and 135 mm to better suit European waters where larger fish occur. Currently, FISHECU operates over six kilometres of extended Nordic gillnets specially con structed to sample benthic as well as epi-, meso- and bathypelagic regions of LIW. The relevance of gillnet catches to the total fish stock estimate has been studied intensely (Prchalova et al., in press).

Lifting of pelagic otter trawl in a reservoir.Trawling. This is possibly the most efficient and most demanding discipline of fish sampling in LIW. HBI has been developing open-water trawling for over two decades but the real progress occurred in 2001, when the first Czech trawler "Ota Oliva" was built. Since then, FISHECU has successfully developed a methodology of fry trawling during whole first season of a fish’s life. At present HBI operates twelve fry trawls of pelagic and benthic construction. These can be used for quantitative fry sampling during nighttime.

Thor Heyerdahl, a new flagship in the trawling fleet of Fishecu.Recently, a significant progress was done in the area of pelagic trawling of adult fish as a result of Czech-Norwegian and Austrian international cooperation. In 2009 “Thor Heyerdahl” a new flagship of the trawling fleet was built (building was greatly supported by a grant from Iceland, Liechtenstein and Norway through the EEA Financial Mechanism and the Norwegian Financial Mechanism).

Laboratory processing of gut contents.Fish food analyses. FISHECU as a unit of HBI is extensively involved in tracing fish feeding niches in LIW. We follow both, bottom-up fluxes (food availability for fish under different conditions) and top-down effects (fish predation on lower trophic levels and the consequences for the water quality). Both, individual-based (foraging efficiency, food electivity) and community-based approaches (food rations and consumption rates, simple bioenergetical models) are being applied. These studies are greatly enhanced by the extensive experience and expertise HBI has gained in its more than 45 years of research into the limnology of LIW.

The set of driftnets for sampling downstream fry drift from the Malše River to the Římov Reservoir.Fry sampling. HBI has completed the development of methodologies for the successful sampling of fry communities. These methodologies include acoustic de tection (Frouzova & Kubecka, 2004), ichthyoplankton nets (Cech et al., 2005), fry seining and trawling (Vasek at al., 2002), point abundance sampling (Hohausova & Jurajda, 2005), and using electrofishing booming boat and drift nets for sampling fry migrating down stream (Peterka et al., 2004). Another important achievement is the assessment of the quantitativeness of fry trawling for sampling pelagic fry communities (Jůza & Kubečka, 2007). All these techniques have been used for studies of fry survival, population recruitment and interactions between juvenile fish and their plank tonic food.

Echograme of sinusoid foraging, a new fish feeding mode discovered during FISHECU investigations (Čech & Kubečka, 2002).Fish behaviour. Behaviour of fish in LIW is still very poorly understood. Our studies concentrate mainly on patterns of fish distribution, horizontal and vertical migrations, use of home range, foraging behaviour, reproductive behaviour, and fish behaviour with respect to sampling gear. To reveal various aspects of fish behaviour we use acoustic techniques, tagging and marking, video, camera and scuba-diving equipment, and appropriate combinations of the above mentioned sampling techniques.

Population dynamics. Data on fish obtained from the above mentioned studies allow interpretation of age groups with the help of aging (analysis) of scales and otoliths. Information on fish age, size-at-age (including back-calculated lengths) and absolute numbers of fish (especially if available in consecutive years) provide the data for survival of cohorts, production and elimination of biomass. Age compositions reflect the reproduction success and survival rates of species under different conditions. The overall biological information allows us to suggest balanced management strategies of fish stocking according to required priorities, such as conservation, fishery priorities, water quality, support of particular species, etc.

Scheme of habitats for fish stock assessment of a typical Biesbosch Reservoir, The Netherlands.Holistic fish stock assessments. Fish stocks of LIW are usually not distributed evenly. Different species and size groups have different affinities to different habitats. Complex assessment of the fish stock begins usually with an inventory of habitats present in a particular LIW. To assess the fish stock HBI attempts to sample every important habitat of a particular LIW by a combination of methods until at least some of them give similar results (species and size com position, relative abundance, CPUE) and there is reasonable confidence in the results. Having completed sampling of all important habitats a mosaic is put together to reconstruct the distribution of fish stock as a whole (keeping in mind the peculiarities and importance of individual habitats). The axes of holistic assessments are usually the quantitative data from the acoustic survey (density, abundance, size structure, biomass), which are complemented by data from other sampling gear used in given habitats. Putting all this information together in a weighted way is very demanding but is an inevitable process where an over all picture of the fish stock, with the absolute importance of different species and age groups, is required.

Echogram of macrophytes from lake Neusiedlersee (horizontal beaming).Other studies. FISHECU takes part in numerous other studies, such as stock assessment in streams and rivers (e.g. electrofishing); impact of different water works and hydropower and nuclear power plants on fisheries; acoustic surveys of macrophytes, sediments and bubbles; food of piscivorous birds and mammals; fish passage through dams and weirs; feeding of fish in rivers and aquaculture ponds; effects of water pollution; and regulations on stream fishes and other organisms.


Selected reference localities and case studies undertaken by FISHECU staff:

Fláje, Klíčava, Lipno, Nové Mlýny I, Nové Mlýny II, Nové Mlýny III, Nýrsko, Orlík, Římov, Seč, Slapy, Těrlicko, Vranov, Želivka, Žermanice and other reservoirs in the Czech Republic

Reservoirs of the Vltava Cascade and Vltava River bellow the cascade, Czech Republic

Acidified lakes and reservoirs in Bohemian Forest and Iser Mountains, Czech Republic

200 km survey of the Elbe River, Czech Republic and Germany

Biomanipulated Bolevecký Pond, Czech Republic

Large shallow lakes: Neusiedlersee, Austria and Balaton, Hungary

Glacial lakes: Wallersee, Hallstättersee (Austria), Feldberger Haussee, Stechlin and Werbellinsee (Germany)

Biesbosch Reservoirs, the Netherlands

Ebro and Aracena Reservoirs, Spain

Thames Valley and Anglian Water Reservoirs, UK

Longitudinal acoustic surveys of Thames and Great Ouse Rivers, UK

Loch Ness and other lochs in Scotland

Ubol Ratana Reservoir, Thailand

Lake Taal, Philipines

Victoria, Minneryia and Udawalawe Reservoirs, Sri Lanka

Lake Turkana, Kenya

Carite, Guajataca, Lucchetti, Dos Bocas Reservoirs, Puerto Rico