Fish sampling in lotic water : a study of the efficiency of the novel Nordic multi-mesh Stream Survey Net

Sammanfattning: A free-flowing stream can offer several ecosystem services. Fish are one of these, and are an important resource for society, both as a food source and as a biological indicator of the water quality, which gives knowledge of the overall health of the stream. The lotic environment in fresh water streams is an important habitat for many fish species. The standard way to catch fish in lotic environments is electrofishing, which in most cases is performed by two persons wading in shallow, hard-bottom parts of the stream with clear water. If the water is deeper an electrofishing boat may be used, but it may be hard to find launching spots for the rather big boat, making it impossible to reach some parts of the river. The Nordic multi-mesh Stream Survey Net (NSSN) is a gill net that is designed to catch fish in lotic environments. The net follows the same idea as Norden nets, with varying mesh size in 12 panels. It works in streaming and still standing waters with a depth of 0.5 meters or more and is deployed on the bottom, parallel with the stream. This study tries to evaluate the efficiency of the NSSN. The survey was performed in Hedströmmen in Sweden during three weeks in July 2015 and was conducted in five sites. The fish community was sampled with the novel Nordic multi-mesh Stream Survey Net. In all, 2,702 fish were caught from 12 different species. To determine the efficiency of the net the CVM-value was calculated for species richness, proportion of individuals and biomass in each location. The data was also compiled to species accumulation curves and compared to data from electrofishing conducted in the same locations. The result in this study shows that the NSSN works well and can be used as a supplementary sampling method when surveying a lotic environment with electrofishing.