BS 14962:2006 pdf download – Water quality – Guidance on the scope and selection of fish sampling methods
6 Fish sampling
6.1 General
Sampling methods are separated into methods by capture (6.2) and data sampling without fish capture (6.3). The principles are explained and the target water types or categories and fish species are given. The suitability of the methods is evaluated depending on the different water categories and their habitats as well as the target species. Target species are those species which can efficiently be caught by a particular method. Tables 4 to 6 provide a synopsis on sampling methods suitable or useful for the determination of the population parameters. Methods not described below may be used in order to obtain additional information. They shall not be used exclusively.
6.2 Fish sampling by capture
6.2.1 Principle of fish capture Fish may be caught by active gear (6.2.2 to 6.2.4) or passive (6.2.5 to 6.2.10). For all gear seasonal aspects shall be taken into account. The efficiency of active gear (electric fishing, seining, trawling) especially may vary considerably depending on the time (day/night) of use. Active gear is characterized by a comparatively short-term use, whereas passive ones normally are exposed over longer time periods. The fishing devices used shall be adapted to the local conditions as well as to the expected fish community. If it is intended to determine the species composition and age structure, an adaptation of fishing gear mesh size(s), day time and season of exposure is required. In order to determine species composition and fish abundance of a certain water body the analysis of professional or non-professional fishery statistics 1) may be considered as suitable, providing the statistics are based on binding regulations. Whether such types of statistics can be used or not, depends on the reliability and exactness of the fishermen’s records. In order to estimate fish abundance from fisheries statistics, information on fishing effort has to be included. The age structure shall be determined by additional sampling. Professional fishermen do not necessarily fish on all species occurring. Here species composition, fish abundance and age structure of the professionally unfished species shall be determined by additional sampling.
6.2.2 Electrofishing General Electricity is led into the water by a special apparatus and fish are caught by the anodic effect (galvanotaxis). Catching fish with electricity is restricted to relatively shallow areas and to stretches of transitional waters with a relatively low conductivity (γ < 6 mS/cm). Electrofishing can be carried out by wading or from a boat. Electric fishing is described in the standard “Sampling of fish with electricity” (EN 14011). Electrofishing by wading Principle: For electrofishing by wading a backpack, other portable device or a generator placed at the bank or in a boat is used. The member(s) of staff using one or more anodes wades/wade through the water and covers/cover all relevant fish habitats. Water types and categories: Electric fishing by wading can be carried out in rivers or transitional waters, categories 1 and 2 and in the littoral zone of larger rivers, transitional waters and lakes, where wading is possible without any risk. Target species: All fish species and sizes living in the areas can be caught. Suitability: Electrofishing is highly suitable for rivers categories 1 and 2, where the whole width of a river can be covered by one or more anodes. The efficiency can be increased by using stop nets at the beginning and at the end of the target zone and by multiple fishing runs. Due to the relatively high conductivity electric fishing is only of medium suitability for transitional waters. Under the conditions described above, samples for species composition, fish abundance and age structure can be collected. Electrofishing from a boat Principle: A generator in combination with the required equipment is placed in a boat, sometimes also on the bank, and the member(s) of staff fish from the boat. Water types and categories: Electric fishing from a boat is possible in rivers where the max. depth does not exceed 2 m and at the relatively shallow sides near the banks and shorelines of deeper rivers, lakes and transitional waters with γ < 6 mS/cm. With adjusted electrofishing equipment the depth range may be extended up to a water depth of 3 m beside the banks or shorelines [27]. Target species: All fish species and sizes which stay in the areas described can be sampled.