The impact of small-scale dredging on the abundance and diversity of juvenile fish

By assignment of the Fisheries Bureau of the Government of Åland, the impact of small-scale dredging on the abundance and diversity of juvenile fish was studied in different parts of the Åland Islands. The impact of large-scale dredging has been studied, as has the direct impact of the dredging process, however not much is known about the long-term effects of smaller dredging sites, such as private jetties and boat houses. Juvenile fish were studied at ten dredging sites during July and August 2021 using two methods: snorkeling and gill net fishing. The dredging sites were in Finström, Hammarland and Sund and had been dredged at different times. During snorkeling, more fish were seen outside the area that had been dredged compared to inside; almost no fish were seen within a dredged area. Gill net data showed that mostly six species of juvenile fish were caught in areas close to dredging sites: bleak, roach, perch, white bream, ruffe, and pikeperch. The occurrence of more fish outside the dredged areas than inside could be due to multiple reasons. Turbidity has previously been thought to impact the behavior of juvenile fish, however the difference in turbidity inside and outside the dredged areas was not consequential and suspended sediment may play a bigger role during the dredging process. Another possibility is the lack of vegetation and the destruction of habitats that occurs due to dredging. Many dredging sites are placed in areas that are ecologically important for fish, such as nursery habitats. More studies are needed during different stages of the dredging process to really consider the impact of dredging on juvenile fish