Fish - inland waters

Two multimetric fish indices are currently used in assessing the status of Swedish lakes (EQR8) and wadeable streams (VIX). Both methods indicate general degradation. The VIX metrics may be used to specify sub-indices for acidity, eutrophication, and hydromorphological pressure. The assessments presume sampling using European CEN standard methods, using Nordic multi-mesh gillnets in lakes and electrofishing in streams. Eight and six metrics, respectively, were calibrated using data available in national databases. The applicability of the indices is restricted to relatively small water courses.

Inland fish in WATERS
In WATERS we aim to broaden the perspective, and suggest modified methods and/or complementary guidelines for assessing the status of fish fauna in large lakes and streams. Development within WATERS will rely mainly on existing fish and environmental data, published experience, and news from other ongoing projects.

For fish in small and medium-sized lakes, site-specific reference values for current and additional metrics will be calibrated in relation to hydromorphological and biogeographical lake characteristics. The number of data from medium-sized lakes and high-altitude lakes might be increased by including sampling occasions when somewhat fewer than the recommended number of gillnets per depth stratum are used. Modified assessment criteria for lakes larger than 5000 ha will be based on monitoring programmes including gillnet sampling methods designed for large lakes. Vertical hydroacoustics is suggested as a complementary sampling method for counting fish. These modified assessment criteria are intended, for example, to handle the larger expected species richness compared to smaller lakes, and the fact that fishing is an important pressure in large lakes. Fishing-related metrics may then be included in a total index for ecological status, or alternatively be used on their own.

The revision of assessment criteria for fish in small and medium-sized streams will use VIX as a starting point, and possibly include new metrics indicating pressure from forestry. Time-series data will be used in evaluating the uncertainty of ecological status assessments. Guidelines will be issued regarding the number of electrofishing sites and the sampling frequency needed for acceptable precision in ecological status assessment. For larger rivers, the suitability of complementary and/or alternative sampling methods will be reviewed, for example, sampling by horizontal hydroacoustics, electrofishing from boats, and gillnets designed for use in lotic water.

WATERS is expected to deliver modified site-specific multimetric fish indices that, compared with present metrics, would be better adapted to larger lakes and streams. General methods based on statistical distributions will be presented. Complementary and/or alternative sampling and analytical methods will be described, as guidelines for status assessment in large or otherwise distinctive lakes and streams.