# Commission Delegated Regulation (EU) 2020/689 of 17 December 2019 supplementing Regulation (EU) 2016/429 of the European Parliament and of the Council as regards rules for surveillance, eradication programmes, and disease-free status for certain listed and emerging diseases (Text with EEA relevance), Division 2: The restricted zone must have been defined on a case-by-case basis and:

Extent: E+W+S+N.I.

(a) it must take into account factors influencing the risks for the spread of infection with Bonamia exitiosa including other establishments and wild molluscs, such as:
(i) the number, age, rate and distribution of the mortalities of molluscs on the establishment or group of establishments infected with Bonamia exitiosa;
(ii) the distance to and density of neighbouring establishments or groups of establishments and wild molluscs;
(iii) the proximity to processing establishments, contact establishments or groups of establishments;
(iv) the species, especially susceptible species and vector species, present at the establishments or groups of establishments;
(v) the farming practices applied in the affected and neighbouring establishments and groups of establishments;
(vi) the hydrodynamic conditions; and
(vii) other factors of epidemiological significance identified;
(b) the geographical demarcation must comply with the following minimum requirements:
(i) the protection zone must consist of an area included in a circle with a radius of at least one tidal excursion or at least 5 km, whichever is larger, centred on the establishment infected with Bonamia exitiosa, or an equivalent area determined according to appropriate hydrodynamic or epidemiological data; and
(ii) the surveillance zone must consist of an area surrounding the protection zone, of overlapping tidal excursion zones; or an area surrounding the protection zone and included in a circle of radius 10km from the centre of the protection zone; or an equivalent area determined according to appropriate hydrodynamic or epidemiological data;
or
(iii) where separate protection and surveillance zones are not established, the restricted zone must consist of an area comprising both the protection zone and the surveillance zone.

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Source: https://www.legislation.gov.uk/eur/2020/689/annex/VI/chapter/4/section/3/division/2 (the official version)
Page: https://openlegislation.uk/eu-regulation-2020-689/annex-VI/chapter-4/section-3/division-2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.