Skagerrak report: small bits do contribute

Twenty years of research in the Skagerrak

Since the start of the international project ‘Save the North Sea (SNS)’ in 2002, fulmars from the Skagerrak area have been investigated by Wageningen Marine Research in Den Helder. The Skagerrak is the marine area between Norway and Denmark. Bird groups from Lista in Norway and Skagen in Denmark are actively involved in the collection of dead beached Northern Fulmars.

Declining number of birds

Although we do not know of an explicit reason, the number of dead beached fulmars collected around the Skagerrak has substantially decreased. In the early five-year periods, tens to more than a 100 fulmars were found. But gradually numbers have dropped to an all time low of only 14 birds during the recent 2017-2021 five-year period. Such number is substantially under the figure of 40 birds considered to be required to produce a reliable average for a specific area and period. Volunteers involved in the collecting of birds, as well as policy makers, were wondering if continuation of their work was of use.

Skagerrak report

In our recently published illustrated ‘volunteer report’ for the Skagerrak area, it is argued that it is certainly of major importance to continue the monitoring project also with smaller numbers of birds. The main point of the work is not to assess the most reliable local figure for plastic ingestion, but it is the trend over the years: is the quantity of plastics in stomach increasing or decreasing, and how do the results of a subarea like the Skagerrak contribute to the larger scale pattern over the whole of the North Sea?

Statistical tests and models

The internationally agreed standard analyses of trends in the quantity of plastics in stomachs of individual birds, suggests that plastic pollution in the Skagerrak is declining. But the test results are statistically not significant for both the long term data (2002-2021) and for the most policy relevant period of the recent ten years ((2012-2021). Recently we have proposed an additional test method that uses the annual proportion of fulmars having more than 0.1 g of plastic in the stomach. That proportion represents the critical element in international policies which aim for a target where no more than 10% of fulmars investigated has more than 0.1 g of plastic in the stomach. For the Skagerrak fulmars, the model does suggest a decrease in plastics, but also this trend is statistically insignificant, with extreme standard errors for future predicted values.

Small local datasets are important

In spite of the fact that within the Skagerrak itself it is not possible to demonstrate statistically reliable trends, the data clearly show patterns with similarity to patterns observed over the North Sea as a whole. Smaller local datasets form an essential component of the statistically reliable conclusions that can be derived from combined datasets for the wider North Sea.