Swedish standard methods for sampling freshwater fish with multi-mesh gillnets : Stratified random sampling with Nordic multi-meshgillnets provide reliable whole-lake estimates of the relative abundance and biomass of freshwater fish in temperate lakes

• The aim of the present paper is to describe a standardised method for sampling fish in lakes, using multi-mesh gillnets. The method provides a whole-lake estimate for species occurrence, quantitative relative abundanceand biomass expressed as catch per unit effort (CPUE), and size structure of fish assemblages in temperate lakes. It also provides estimates comparable over time within a lake, and estimates comparable between lakes. The method is the result of a development that has been going on for several decades at the Institute of Freshwater Research, Drottningholm, and an extensive cooperation within a joint Nordic workshop (Nordic Freshwater Fish Group;NOFF). The sampling method is commonly used in national and regional fishsampling programmes in Sweden. The paper provides information on sampling routines, data handling and reporting, sampling of fish for age- and growth analyses as well as applications and further treatment of data.The sampling procedure is based on stratified random sampling. The sampled lake is divided in depth strata and random sampling is performed within each depth stratum. Sampling of benthic fish is performed with NORDIC multimesh gillnets which are 30 m long and 1.5 m deep. The gillnets are composed of 12 different mesh-sizes ranging between 5 to 55 mm knot to knot following a geometric series. Gillnets used for sampling pelagic fish are 27.5 m long and 6 m deep, with the smallest mesh-size being 6.25 mm. The number of efforts needed to allow detection of 50% changes in relative abundance between sampling occasions, range between 8 gillnets per night (efforts) for small, shallow lakes, up to 64 efforts for lakes of about 5 000 ha. When less accurate estimates of abundance is needed, an inventory sampling procedure may be used, thereby reducing the number of efforts needed.Correction factors for gillnet selectivity of the NORDIC gillnets has been estimated six fish species, common in Nordic lakes. Fish sampling performed with an earlier Swedish multi-mesh gillnet standard may be transposed to the NORDIC gillnets, and at the moment correction factors are available for perch (Pereafluviatilis) and roach (Rutilus rutilus). The sampling methodonly provides abundance estimates for fish larger than about 5 mm total length of fish species catchable in gillnets. Abundance estimates of some less catchable species, such as eel (Anguilla anguilla), burbot (Lota lota) and pike (Esox lucius), as well as small Y-O-Y individuals, may be underestimated.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Fisk- och akvakulturforskning (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Fish and Aquacultural Science (hsv//eng)

Nyckelord

freshwater

sampling

fish

lake

gillnet

routine

data handling

reporting

abudance

sötvatten

provtagning

fisk

sjö

nät

rutiner

datahantering

rapportering

överflöd

National

Nationellt finansierad miljöövervakning

Ett rikt växt- och djurliv

A Rich Diversity of Plant and Animal Life

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