Feld L, Jakobsen HH, Göke C, Ellegaard-Jensen L, Hendriksen NB, Rømer JK & Jensen AN. 2022. Sanitary survey rapport 17: Venø Bugt, Kås og Salling. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 96 s. - Teknisk rapport nr. 249
http://dce2.au.dk/pub/TR249.pdf.
Regulation (EU, 2019) of the European Parliament and the Council of 15 March 2019 lays down specific rules for organising official controls on products of animal origin intended for human consumption. Classification of production areas for live bivalve molluscs and the associated sampling plan must be based on so-called ”sanitary surveys”. A sanitary survey assesses the interactions between potential sources of microbial pollution, climate conditions and oceanography in the area. The EU Commission's guidance for conducting a sanitary survey forms the basis for this report. However, in some instances, the Danish practice for microbiological sampling frequency and the previous classification are used. The Danish practice is described in the Executive order on mussels etc., called “muslingebekendtgørelsen” (BEK no. 1793 of 02/12/2020), summarised in Appendix 7.
The report covers the Danish area south of Mors as a part of Limfjorden, which includes ten production areas that are located in Venø Sund (P5 and P6), Venø Bugt (P7 and P8), Kås Bredning (P9), Sallingsund (P11 and P13), Lysen Bredning (P12), Dråby Vig (P14) and Sønder Bredning (P15). In the report figures, the covered production areas are marked with a thick blue marking.
The report is a revision of the previous report for the area south of Mors (Larsen m.fl., 2017). Experience from past sanitary surveys form the area has shown a difference in the significance of the topics covered in the individual appendices for potential microbiological contamination of the production areas (https://ecos.au.dk/forskningraadgivning/muslingefiskeri). In addition, for some of the topics, no significant changes were expected to have occurred within the previous 5-6-year period. Therefore, it was decided that no new data should be collected for the appendices covering these topics. Instead, the main report refers to the corresponding appendix in the previous report (Larsen et al., 2017).
In the area south of Mors, there has historically been an important commercial fishery of particularly blue mussels and cockles with large harvests of several tonnes from the areas P7, P8, P9, P11 and P15 and more scattered from single years also from P5, P6 and P13, while from P14 harvest has only been registered in 2014. The harvests from individual production areas have also varied considerably between years. Apart from blue mussels and cockles, the fishery for other types of mussels has included common starfish and oysters. Permissions for mussel farming are registered for P5, P9, P11, P12, P13, P14 and P15, where thereis active production for harvesting, except for P11.
The report was supported by publicly available data from the monitoring of microbiological contamination in the area south of Mors. The concentrations of E. coli and Salmonella were determined in mussel samples taken at different sampling points within each production area. The report identifies the most precautionary fixed sampling points for future monitoring. Part of the data used in this report was collected from web pages belonging to, for instance, municipalities and Statistics Denmark (Danmarks Statistik). It cannot be guaranteed that the accessed data will be persistently available.
From the Danish mussel surveillance, a broad set of historical data is available on E. coli in mussels etc., collected from the production areas within the area south of Mors throughout the last ten years (2012-2021). During this period, 3342 samples were analysed for E. coli from the whole area, including 1659 samples of mussels from the sea bottom and 1683 samples from production lines. The corresponding numbers from the latest 3-year period (2019-2021) were 668 samples from the sea bottom mussels and 783 from the production line mussles. An adequate number of samples have been collected from all areas to qualify for permanent classification, where A-classification is suggested for P6, P11, P13 and P15 and B-classification for P7, P8, P9 and P12. Exceptions are P5 and P14, for which too few samples have been analysed for E. coli, thus requiring an extended sampling effort to allow classification.
The samples analysed consisted primarily of blue mussels (Mytilus edulis) but also cockles. In minor numbers, oysters (unspecified or European oysters (Ostrea edulis) or Pacific oysters (Crassostrea gigas)) were collected for analysis. Additionally, 343 samples were analysed for Salmonella (2012 to 2017), and one of these samples was positive for P14.
The overall data from the area south of Mors revealed good microbiological hygiene, but with a significant difference between the individual production areas. In six out of the ten areas, the samples showed a low level of E. coli, with 97-100 % of the investigated samples from the latest 10-year period representing A-level (≤ 230 MPN E. coli/100 g). For the areas P7 and P8, the levels of E. coli were a little higher; only 95-96 % of the samples were at A-level, and for the areas P5 and P12 only 91-93 % of the samples were at A-level, with a decline to 87% in P5 during the latest three years (representing mussels solely from production lines).
A statistical analysis of the microbiological data furthermore showed that there was a significant difference between the samples collected within the same area but in different seasons. A relatively lower number of samples were positive for E. coli in spring compared to summer, with the highest ratio of positive samples occurring during winter. Likewise, there was a significant difference between the samples collected from the different years, with only 20 % of the samples being positive for E. coli in 2013; the highest ratio of 59 % was observed in 2020.
Based on an assessment of sources and transport routes for microbiological contamination (sanitary survey), a microbial monitoring programme was recommended for each of the production areas P5-P9 and P11-P15. In each of the recommended monitoring programmes, proposals for a sampling location, classification status (preliminary or permanent) and a sampling plan were outlined.
Based on the results from the sanitary survey of the production areas, supported by the historical data sets on the number, frequency and E. coli concentration, it was assessed that all production areas within the area south of Mors, with the exception of P5 and P14, were considered suitable for permanent classification. Accordingly, it is suggested that the areas P6, P11, P13 and P15 are awarded A-classification and P7, P8, P9 and P12 are given B-classification. For P5 and P14, there is an absence of samples (apart from two samples from 2019) analysed during the last three years (2019-2021), and these areas can therefore not be classified. If unclassified areas are to be upgraded to permanent classification, the EU guideline requires that the collected data should include at least 12 samples for the latest six months or 24 samples over the last three years.
The report is divided into main chapters that provide a summary of identified microbiological contaminants. Appendices 1-4 serve as a starting point for the main chapters. In addition, relevant data representing characteristics of the areas, as described in the previous sanitary survey for the area south of Mors (Larsen et al., 2017), has been included. Appendix 5 is a detailed review of all historical microbiological data from mussel monitoring consisting of the fishery’s own check and the Danish Veterinary and Food Administration’s[1] verification projects of the industry’s microbial monitoring. It was decided that a so-called ”shoreline survey” is unnecessary because all possible sources of sanitary contamination were described in the sewage plans for the cities in the area, the beach water quality monitoring and in the analyses of the Ministry of Environment and Food under the auspices of the Water Framework Directive.
