On behalf of Blekinge County Administrative Board Aquabiota mapped the fish community in the Gåsefjärden area in Kalskrona archipelago using eDNA and net fishing, as well as compared these methods.
In the month of August 2019, 45 stations were sampled by net fishing and 17 by eDNA, of which 16 stations were mutual for both two methods. In total 30 different species of fish were identified including 3 red listed species, eel, cod, and freshwater bream.
All together the samplings show that the fish community to a large extent is characterized by freshwater fishes including perch and common roach. In the outer parts of the area the occurrence of marine species increases such as herring, sprat, and cod.
At the 16 stations where both methods were used a total of 6 species were identified with nets and 12 with eDNA. The fishes detected by eDNA includes species that seldom are captured with nets, such as pike, three-spined stickleback, eel, and sculpins.
The two samplings methods work well together, contributing with different sort of information. When investigating fish biodiversity eDNA is the preferred method, being beneficial in terms of cost-effectiveness as well as in ethical and conservation matters. Net fishing is preferred when information about species biomass and lengths is of interest.
The report (in Swedish) can be found here.
Map over the survey area showing the number of fish species detected per location with 45 gillnet stations (left), and 16 stations where both gillnets (middle) and eDNA (right) were used. The size and colour of the points are scaled after the number of species detected. Background map, Swedish land survey, CC0.