Identification

Identifier

NRW_DS125743

Alternative Title

• NRW Freshwater Fish Surveys

Metadata Language

English

Lineage

A strict methodology is applied when sampling for freshwater river fish. There is a core network of sites which are monitored on an annual basis, and also catchment-wide surveys on a six-year rolling programme. These sites are located in habitat types suitable for the respective fish species. In addition, sites may be sampled for investigative work, or on an ad hoc basis. Sampling areas are commonly 50 metres long and the full width of the river and may embrace different flow types and substrate. For Catch Per Unit Effort (CPUE) survey strategy the effort is based on a time measurement. Electric fishing is the most commonly used sampling method, although alternative methods are available for different strategies, such as netting and trapping. Once a sample of fish is collected, they are immediately identified in the field, measured and counted and then released alive into the same section of river from where they were captured.

For many of our surveys we record an NGR at the site because this acts as a central/representative location around which we collect lots of samples. An NGR is then also recorded against each of the samples to give a more accurate sampling location.

Redactions

Some information has be redacted to make the data openly available. This includes:

Third party data

Data collected for ongoing investigations

Cancelled or incomplete surveys

Update Frequency

This data is continually update with the most surveys undertaken in the summer. Data from survey seasons is often not enter at the time of capture and can be several months before its is entered into the system. The external dataset is updated monthly to include new data, and may also contain corrections to previously published data due to quality assurance work.

Information Warnings

Freshwater fish survey data is available from 1974 to present. A caveat being that historical data are sporadic until 2001. This is because fish survey data collected before 2001 were often saved in local databases and not the national ones (KiEco and formerly NFPD).

Fish surveys are carried out by a range of survey methods, the data from one survey is not necessarily directly comparable to another. For example, the total fish count may be based on multiple or single run surveys or Catch Per Unit Effort (CPUE) surveys. The user is recommended to check the survey method used in the data provided.

We do our best to avoid data quality problems, but as these datasets reflect the data we hold, they may contain errors.

Dataset Reference Date (Publication)

2026-10-27

 

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