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Review of Management Unit boundaries for cetaceans in UK waters (2023) 2023


In 2015, the Inter-Agency Marine Mammal Working Group (IAMMWG) defined Management Units (MUs) for the seven most common cetacean species found in UK waters (JNCC Report 547, IAMMWG 2015).

This report reviews information published since 2015 on the populations of the seven cetacean species and identifies whether there is sufficient evidence to warrant a change to any of the MU boundaries. Updated abundance estimates in line with amendments made in this review are also provided. Information provided here supersedes IAMMWG 2015 (JNCC Report 547) and IAMMWG 2022 (JNCC Report 680), although the principles underlying the delineation of MUs and calculation of abundance estimates remain unchanged, and both reports (JNCC Reports 547 and 680 (IAMMWG 2015, 2022)) should be referred to in conjunction with this report.

Accompanying the report are a collection of shapefiles that set out the updated boundaries of the Management Units (MUs) for the seven cetacean species:

  • bottlenose dolphin (Tursiops truncatus) (revised May 2023),
  • short-beaked common dolphin (Delphinus delphis),
  • harbour porpoise (Phocoena phocoena),
  • minke whale (Balaenoptera acutorostrata),
  • Risso’s dolphin (Grampus griseus),
  • white-beaked dolphin (Lagenorhynchus albirostris),
  • Atlantic white-sided dolphin (Lagenorhynchus acutus).

You are free to re-use the Management Units boundary data subject to the terms of the Open Government Licence. If you re-use this data you must acknowledge the source of the information in your product or application by including or linking to the following attribution statement: "Contains JNCC © copyright and database right 2023. Boundaries defined through discussions of the Inter-Agency Marine Mammal Working Group (IAMMWG)."

This report, first published in March 2023, was republished in May 2023, following the resolution of a minor discrepancy in the management units for bottlenose dolphin. The accompanying management unit shapefiles for bottlenose dolphin have also been replaced.

This report may not be fully accessible for all users. If you need a copy in a different or more accessible format, please contact

Resource type Publication

Topic category Environment

Reference date 2023·03·01

IAMMWG. 2023. Review of Management Unit boundaries for cetaceans in UK waters (2023). JNCC Report 734, JNCC, Peterborough, ISSN 0963-8091.

This report was prepared by the Inter-Agency Marine Mammal Working Group (IAMMWG) which comprises representatives of the UK Statutory Nature Conservation Bodies (Natural England, NatureScot, Natural Resources Wales, the Department of Environment, Agriculture and Rural Affairs of Northern Ireland, and JNCC).

Responsible organisation
Communications, JNCC publisher

Limitations on public access No limitations

Use constraints Available under the Open Government Licence 3.0

Metadata date 2023·05·31

Metadata point of contact
Communications, JNCC

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