Density and biomass of fish taxa from three chalkstreams in the Wessex chalk area: Nine Mile River, River Till and River Wylye. Data were collected on five occasions, between October 2012 and October 2013. The density of fish taxa at each of the three streams was estimated using benthic fish sampling and multi-pass electrofishing. The mean biomass of individuals of each taxon at each site on each occasion was then applied to the density estimates to derive an estimate of the biomass per m2 of each taxon at each site on each occasion. Data were collected to quantify food webs detailing the flux of mass and nutrients between nodes of the food web. This dataset was created as part of work package 3.2 of the Wessex Biodiversity & Ecosystem Service Sustainability (BESS) project.
Publication date: 2017-06-26
Samples were collected on five separate occasions from the three sites. Sampling did not occur during the salmonid breeding season, December to March, so as not to disturb redds. Protocols and standard procedures were strictly followed for benthic fish sampling and electrofishing but there was no formal quality assurance procedure, such as repeat surveying of the same reach on a different day within the same sampling period. Electrofishing was undertaken by fully qualified and very experienced fish biologists (Bill Bellamy and Luke Scott) from the Game and Wildlife Conservation Trust.
Fish populations were assessed by multi-pass electrofishing. Population density estimates were derived using the the Zippin maximum likelihood method (Zippin, 1958). As electrofishing is not particularly effective at catching certain benthic species e.g. bullheads, stone loach, we used a modified Hess sampler (0.12 m2) to assess populations of these species, deployed 20 times on each date, using a stratified-random regime. The mean biomass of individuals of each taxa captured at each site on each occassion was determined using length-mass regressions, and multiplied by the density estimate to derive a biomass estimate.