The use of regurgitated pellets from the great cormorant to detect the presence of the round goby

Abstract: The round goby (Neogobius melanostomus) is an invasive alien species that poses one of the greatest threats to biodiversity and ecosystem services in Sweden today. The round goby originates from the Black Sea and Caspian Sea but has in recent decades rapidly spread with global shipping traffic to new areas in Europe and North America. To protect indigenous species and habitats there is a need for early detection methods of round goby. The great cormorant (Phalacrocorax carbo) is despised by the public because it competes with the fishing industry and its feces kills the vegetation at its breeding sites. However, the great cormorant can potentially provide valuable information regarding the spread of invasive fish species. The purpose of this pilot project is to investigate whether the regurgitated pellets of great cormorants can be used to detect the presence of the invasive alien species round goby. Regurgitated pellets were collected from Medholmarna and Norra Röden. The QIAGEN DNeasy Blood & Tissue Kit protocol was followed to lyse and extract DNA, while the Qubit fluorometer and digital PCR (dPCR) were used to detect and quantify the amount of round goby DNA. The DNA concentration in the pellets from Medholmarna ranged from 14.4 ng/μl to 194 ng/μl (mean: 68.395 ng/μl), compared to 14.4 ng/μl to 150 ng/μl (mean: 58.885 ng/μl) from Norra Röden. In the samples from Medholmarna, six out of ten pellets contained round goby DNA with an average concentration of 0.295 (± 0.305) DNA copies per μl. In the samples from Norra Röden, eight out of nine pellets contained round goby DNA with an average concentration of 32813 (± 83257) DNA copies per μl. The difference in round goby DNA concentration between the sites suggests that the round goby is more established in the area around Norra Röden than around Medholmarna. The results from this project indicate that the QIAGEN DNeasy Blood & Tissue Kit, Qubit fluorometer, and dPCR are three practical tools to analyze dietary samples and that great cormorant pellets can be used as an additional method to detect the presence of the round goby. Large-scale projects and analysis of great cormorant pellets can provide important information for future conservation efforts and the protection of marine ecosystems.