THE EU WATER FRAMEWORK DIRECTIVE

BIOLOGICAL ASSESMENTS - FISH STOCKS

Swedish standard methods for sampling freshwater fish with multi-mesh gillnets

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 abundance and 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 co-operation within a joint Nordic workshop (Nordic Freshwater Fish Group; NOFF). The sampling method is commonly used in national and regional fish sampling 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 multi-mesh 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 (Perca fluviatilis) and roach (Rutilus rutilus). The sampling method only 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.


Fisheries Proposed For Fish Stock Assesment

It is our understanding that designated lakes above 50 hectares are to receive biological analysis. According to a discussion document produced by the Envirenmental Protection Agency (EPA) termed "National Lake Water Quality Monitoring Programme", 205 lakes have been chosen to satisfy the biological monitoring requirements of the WFD. Many of these lakes have not been gillnetted in any way before now, while others have.

A number of the lakes for example, designated as WFD >50 ha within the EPA document are:
Lough Muckno, Lough Egish, Lough Avaghon, Drumlona Lough, Lough Ramor, Lough Sillan, Tacker Lough, Lough Gowna, Lough Oughter, Lough Forbes, Kilglass Lough, Lough Key, Lough Ree, Templehouse Lough, Lough Gara, Lough Gill, Lough Derg, Blessington Reservoir, Lough Derravaragh, Lough Iron, Lough Glore, Lough Mask, Derryhick, Levally Lough, Lough Urlaur, Lough Graney, Inchiquinn Lough, Doon Lough, Lough Allua and Inniscarra Reservoir.

At present, it appears undecided who will carry out the sampling of fish stocks. The Central Fisheries Board does not have the manpower or resources to carry out the level of testing required and therefore it may fall on an independent or private body to do so.

At present it is also unclear at what frequency the sampling will take place. IFPAC is seeking a meeting with the EPA to try to clarify the issue of fish stock assessments within the WFD.

An improvement in water quality under the WFD has to be welcomed but an over-riding concern has to be the level of fish mortalities, which could take place within the implementation of the directive. Indeed, fish should not become expendable, particularly in the face of any apprehension to introduce effective measures to improve water quality.

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