Sammendrag
Rapporten oppsummerer anbefalingene fra fagråd for klassifisering av ferskvannsfisk ble nedsatt for a gi forvaltningen rad om egnede miljokvalitetsnormer (klassegrenser) for fisk som indikator pa sentrale pavirkningsfaktorer i vassdrag. Vurderingene av fiskebestandens tilstand anbefales gjennomfort ved hjelp av et ”klassifiseringstre”, som er en strukturert dokumentasjon av ekspertvurderinger av dagens tilstand i vannforekomsten sammenlignet med en forventet referansetilstand. Dette er en generell vurdering av tilstand uavhengig av pavirkningstype. Vurderingene blir sikrere jo bedre datagrunnlaget er, men uansett er det viktig at alle vurderinger dokumenteres og kvalitetssikres. Referansetilstanden for fisk må i stor grad antas a vare lokalitetsspesifikk, det vil si at fiskebestandens naturlige tilstand i stor grad ma defineres for hver enkelt vannforekomst. Vi har imidlertid begynt utvikling av mer typespesifikke referanseverdier for laksefisk i små elver og bekker og pelagisk fisk i innsjoer. The report summarizes work to develop methods for using data on the fish stocks as an ecological quality element for classification of water bodies (lakes and rivers) under EU’s Water Framework Directive in Norway. The aim of the work in the “Advisory Committee on Fish in the Water Directive” established by the Directorate for Nature Management (presently the Norwegian Environment Agency) in 2011was to: Develop systems for characterizing the extent of impact by selected human activities by recording certain parameters on fish populations. Identify those parameters which may be applied in the definition of ecological status class limits, and recommend how these parameters should be treated. Describe criteria to identify situations when the ecological status of the fish populations is in in a less than Good status, i.e. when mitigating actions are required concerning the water body, or alternatively, the water body has to be classifies as Heavily Modified. Fish is considered the most sensitive quality element in relation to: 1) hydromorphological changes (i.a., migration barriers and habitat fragmentation), 2) acidification, and 3) introduction of alien species. The reference condition for fish stocks in Norwegian lakes and rivers must to a large extent be locality specific, due to the immigration history of freshwater fishes and the topography of the country. The assessment of the status of fish populations should be guided by a system of expert judgement, which even when good data are available, should be applied in the final classification of the water body. Water management, ecological status, freshwater fish, pressures, Vannforvaltning, økologisk tilstand, ferskvannsfisk, påvirkninger