Feld L, Jakobsen HH, Göke C, Hendriksen NB, Rømer JK & Jensen AN. 2021. Sanitary survey rapport 15. Løgstør Bredning. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 84 s. - Teknisk rapport nr. 213. http://dce2.au.dk/pub/TR213.pdf
Regulation (EC) No 854/2004 of the European Parliament and the Council of 29 April 2004 lays down specific rules for the organisation of 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 is an assessment of the interactions between potential sources of microbial pollution, climate conditions and oceanography in the area. The EU Commission guidance for elaborating a sanitary survey has formed the basis for this report. However, in some instances, the Danish practice regarding microbiological sampling frequency and the previous classification based on this are used. The Danish practice is described in ”muslingebekendtgørelsen”, which is summarised in Appendix 7.
The report covers the Danish area Løgstør Bredning, which includes eight production areas within the central part of The Limfjord, and the entire Løgstør Bredning (P33, P34, P38 and P39) and the bordering areas Bjørnsholm Bugt (P37, P16), Blinderøn (P36) and Livø Bredning (P35).
The report is a revision of the previous report for the Løgstør Bredning (Larsen et al. 2017). Experience has shown a difference in the significance of the topics covered in the individual appendices for potential microbiological contamination of the production areas. In addition, for some of the topics no significant change is expected to have occurred within a 5-6 year period. Therefore, it was decided that no new data will 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).
From all of the eight production areas in Løgstør Bredning, considerable commercial fishing for mussels has been registered within the latest period from 2012-2020. The catches have primarily consisted of blue mussels (Mytilus edulis) with annual amounts of 0-7,844 tonnes per year but with a large year-to-year variation. In addition, catches of other mussels, including cockles and oysters, have also been registered. No valid permissions for mussels farming are registered within Løgstør Bredning.
The report is supported by publicly available data from the monitoring of microbiological contamination in the area Løgstør Bredning where the concentrations of E. coli and Salmonella were determined in samples of mussels at different sampling points within each production area. The report points to the most precautionary fixed sampling points for future monitoring. Part of the data used in this report has been collected from web pages, 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 historical data set is available of E. coli in mussels etc., collected from all production areas within Løgstør Bredning through the last ten years (2011-2020). During this period, 1,104 samples were analysed for E. coli from the whole area. From the latest 3-year period (2018-2020) some 53 to 65 samples have been collected from each of the areas P16, P33, P34, P35 and P36, which qualify for classification of the areas. For P37, P38 and P39, an inadequate number of samples were collected to obtain classification. From P38 and P39, no samples were available from the last year (2020) and from all three areas, < 24 samples were available from the 2011 to 2020 period.
The samples analysed were primarily collected from the bottom, except in P16 where mussels were collected from a single commercial production facility that is no longer active. The majority of the samples consisted of blue mussels, but a smaller number of samples were also analysed from oysters, mostly European oysters (Ostrea edulis), but also Pacific oysters (Crassostrea gigas) as well as a few non-specified oysters. Additionally, 262 samples were analysed for Salmonella (during 2011-2017), but all samples were negative.
Overall, the overall data from the area Løgstør Bredning revealed good microbiological hygiene in the investigated samples with 99.8% of the 1,102 samples at low levels ≤ 230 MPN E. coli/100 g, and out of these, 890 samples (81%) were below the limit of detection with < 18 MPN E. coli/ 100 g. In only two samples (0.2%) collected from P38 and P39, respectively, in 2015, E. coli was detected in concentrations at B-level 230 < MPN ≤ 700 E. coli /100 g.
In summary, the sanitary survey of Løgstør Bredning identified good micro-biological hygiene with low levels of microbial contamination in the analysed samples from all production areas. However, only a limited set of microbiological data exists from the areas P37, P38 and P39 from the latest 3-year period. Consequently, the data was insufficient for classification of these three areas. A statistical difference (P<0.005) was observed between the production areas with P16 having a larger proportion of positive E. coli samples (33%) and P36 and P38 having the lowest proportion (12%) of detected E. coli. Furthermore, a significant time-of-year variation was found, with a higher number of positive samples observed during winter (46%) and, to some extent, autumn (21%) compared to spring (12%) and summer (13%). Statistical differences were not observed in the amount of samples positive for E. coli during the latest 10-year period.
Based on an assessment of sources and transport routes for microbiological contamination (sanitary survey) verified as far as possible against historical microbiological data from Løgstør Bredning, a microbiological monitoring programme was recommended for each of the production areas P16 and P33-P39. 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 production areas P16, P33, P34, P35 and P36 were suitable for permanent classification. This implicates a future sampling frequency of at least eight samples per year over a three-year period. Assignment of a permanent classification was not possible for the three production areas P37, P38 and P39 due to an insufficient number of analysed samples (less than 24) within the past three years and/or lack of sampling in the past year (2020). 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 data from 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 starting point of the main chapters, and in addition, relevant data representing the characteristics of the area, as described in the previous sanitary survey for Løgstør Bredning, have 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 have been 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.