Fish sampling uses a multihabitat approach. Various habitats are sampled in proportion to their representation within the sampling reach. Each reach should contain riffle, run, and pool habitat samples, if possible. Prior to sample collection, a habitat assessment should be performed. Physical and chemical parameters should be measured at the same time as fish sampling to specifically characterize the habitat.
The single most efficient method for collecting a representative sample of stream fishes is through electrofishing (click for image). There are several different types of electrofishing equipment available; the type used will depend on the habitat conditions, personnel experience, and agency resources. Because of the hazardous nature of this method, the fish collection team must be adequately trained and experienced.
Block nets should be set up at the ends of the reach before sampling begins. Electrofishing collection should begin at a shallow riffle at the downstream limit of the sampling reach, and it should end at a similar riffle at the upstream limit of the reach. All of the wadeable habitats within the reach should be sampled. Fish should be held in livewells (or buckets) until they can be identified and counted. (click for image) Fish must then be identified to species or subspecies. If this cannot be done in the field, then the unknown specimen should be preserved in a 10% formalin solution and labeled for laboratory identification (but this is not recommended in rare fish habitats). The percentage of each habitat type should be estimated in the reach and included on the field data sheet. For more details about electrofishing methodology and options, click here.
As with the other assemblages, a multimetric approach is used that incorporates the zoogeographic, ecosystem, community, and population aspects of fisheries biology into a single ecologically based index of the quality of the water resource. The RBPs multimetric index integrates different types of information about the fish assemblage into an ecologically based index that is used to make planning and management decisions. It is an aggregation of twelve biological metrics that are based on species and trophic composition of the fish assemblage as well as the abundance and condition of fish. These metrics work to quantify the professional judgements of biologists into a measure that will indicate the quality of the fish assemblage.
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