The Potential to Target Smaller Sized Baltic Herring to Decrease the Dietary Exposure - an Assessment Based on Dioxin Samples from the Southern Baltic

Sammanfattning: PCDD/Fs and dl-PCBs, or more commonly referred to as dioxin and dioxin like substances are compounds present in our surrounding environment. As some congeners of these have been shown to be toxic, they are regulated under the Stockholm Convention. As dioxins are persistent in biota and have lipophilic properties they are seen accumulating in lipid rich fish in the Baltic, one of the affected species being herring (Clupea harengus). The aim of this study was to assess if a fishery targeting smaller herring (length wise) could affect the expected dietary exposure to dioxins via herring and what efficiency and ecological effects such a measure could have. Herring is a key species for the commercial fisheries with regards on volume. The vast majority goes to industrial purposes but Baltic herring are also prepared for human consumption. The EU Regulation 2023/915 manage the allowable dioxin and dl-PCBs levels in wild caught fish that is put on the European market. Sweden and Finland are granted a derogation from these threshold values and only since 2018 the export ban, to EU, of herring (>17cm) caught in sub division 25 of the Baltic Sea were lifted. Eight pooled samples were sent to analysis and all samples had a dioxin content well below EUs threshold values. As no correlation could be seen for all samples between length and dioxin content, the correlation found for one site were used as a "maximum" scenario in the model predicting dioxin content in the catches. A fishery targeting shorter herring could have positive effects on the dietary exposure to dioxins by approximately decreasing the TEQ with 0.8 pg/g w.w. if the target length of herring in the catches decreases from 26 to 16 cm. The variable weight-at-age had great impact on the results affecting the efficiency a targeted fishery actually would have. With the presumption that a targeted fishery on smaller herring only would be applied on the proportion of the catches that are allocated to human consumption the expected ecological effects were predicted to be low. Though as this thesis assessment included many assumptions and neglected parameters the results should be seen as highly approximate.