Round goby – turning risk into resource

The project showed through analysis of monitory fishing data and experiments that the round goby is both a risk and a resource for native fish fauna where predatory fish are favoured while some flatfish and salmonids are disadvantaged. According to our modelling, this had a negative effect on the value of recreational fishing, while the economic effects on commercial fishing can be both positive and negative. The project also showed in field studies, experiments and modelling of fish monitoring data that predatory fish have the potential to limit the density of the round goby. Genetic analyses showed that investigated barriers in river systems can slow but not prevent dispersal, as well as experiments showed that the species can migrate in a vertical slot array (a common type of fishway) even if higher speeds seem to limit it. In cooperation with fishers, fyke nets were modified so that they caught round goby efficiently while releasing unwanted bycatch. 

Work package 1 - Impacts on fish communities and ecosystem services

We analysed catch per effort in monitory fishing with nets from four coastal areas in the Baltic Sea with data series of up to 23 years. According to our models, the abundance of perch, cyprinids, predatory fish and ruff increased, while the abundance of whitefish and flounder decreased after the invasion of round goby. (Naddafi & Florin 2025). 

Experiments with spawning salmon in the stream aquarium at the Fisheries Research Station in Älvkarleby showed that the time to spawn was extended in the presence of round goby. (Wallin Kilhlberg et al. 2023).

 If the round goby continues to spread, our economic analyses showed that in 10 years' time, recreational fishing may have decreased by several hundred million in terms of present value. However, this assumes that the goby itself does not bring any value. The effect on commercial fishing is more difficult to analyse because it depends on whether the species is limited by a quota or not, and because of a lack of data on the impact of round goby. There are scenarios where the fishery or the consumer both gain and lose financially if the round goby continues to increase. (Bostedt et al. 2025, Florin et al. 2026).

Work Package 2 - Limiting round goby spread

Genetic analyses of round goby from different sides of potential barriers in four major rivers in central Europe showed that barriers in rivers can limit the spread of round goby, but it was not possible to say which of the barriers were most effective. However, it was clear that the more barriers, the worse the spread of the round goby – even if there were sometimes fish passages at the barriers. (McCallum et al. 2025).

In Vattenfall's Laxelerator, a vertical slot array was built to study the migratory ability of round goby and compare it with native species such as perch, bullhead and seatrout. The experiments showed that the round goby can make its way in these arrays at waterspeeds of up to 0.68 m/s, although it was clear that it was a much worse swimmer than the native bullhead. Experiments with bubbles as a barrier did not yield unambiguous answers. (Junehag 2023, Florin et al. 2026) 

Work package 3 – Limiting round goby density

The round goby often becomes a dominant species in the fish fauna in invaded areas. It is difficult, if not impossible, to eradicate it, but by limiting its density, negative effects could be mitigated. A possible way to limit the species could be through intensive fishing, and in this project, our analysis of monitory fishing data and compilation of existing knowledge from literature and experts showed that catches are highest in shallow water (<10m) during the period May-August. Comparison between gillnets and fyke nets showed that fyke nets usually gave a higher catch per effort of round goby, while the bycatch was lower.

Based on the above, fyke nets were chosen as gear in pilot trials with professional fishers in Blekinge and Stockholm County. The gear was modified with different types of entrances and by moving the location of escape openings. The best results, in the form of large catches of round goby and perch but low of eel, were achieved with larger variants of the gear and the escape opening placed in the upper part of the gear. To develop a commercial fishery of the species when there is no market for round goby in Sweden, a profitability could arise if the fishing was combined with fishing for other coastal fish such as perch. (Florin et al. 2026)

The round goby can also be a valuable resource for fish-eating birds and fish. Analysis of stomach contents of large perch (>20 cm length) collected monthly for a couple of years in the Blekinge archipelago showed that round goby was the dominant species in the diet based on biomass and particularly dominated in autumn and spring. (Arnet 2021). In various experiments, the perch's handling time of different sizes of round goby was investigated and the exchange value was calculated (Karlsson 2023). Perch were also found to prefer round goby to stickleback in forage selection experiments (Blanco 2023). 

Overall, this showed that predatory fish such as perch have the potential to regulate the density of round goby. We also analysed catches per effort in monitory fishing from four coastal areas in the Baltic Sea to see if the density of different fish species affected the density of round goby. Our modelling showed that increased abundance of predatory fish such as large perch, cod, pike and pike-perch reduced the density of round goby. Predatory fishes today are in many cases repressed and efforts to benefit predatory fish populations, such as protection and restoration of spawning areas, could contribute to a higher resilience of the ecosystem against the invasion of round goby.

Team

This was a large collaborative project between departments at SLU, Lund and Umeå University. We also collaborate with researchers at other universities and had an international reference group consisting of researchers, fishers, and managers. 

Publications

Florin, A.-B., Naddafi, R., Ljungberg, P.,Persson, A., McCallum, E., Persson, L., Tanmario, C., Bostedt, G. Svartmunnad smörbult – förvandla risk till resurs. 2026. Naturvårdsverket Rapport 7207. https://www.naturvardsverket.se/publikationer/7200/978-91-620-7207-0/.

McCallum ES, Sefc KM, Brodin T, Burkhardt-Holm P, Bussmann-Charran K, Florin A-B, Geist J, Janáč M, Jurajda P, Martin JM, Pander J, Bose APH. 2025 Round goby population differentiation across river barriers in Central Europe. Aquatic Invasions. 20 (3), 355-370. https://doi.org/10.3391/ai.2025.VOL.ISS.152950

Naddafi, R., & Florin, A. B. 2025. How does round goby (Neogobius melanostomus) affect fish abundance in the Swedish coastal areas of the Baltic Sea?. PloS one, 20(2), e0316546. https://doi.org/10.1371/journal.pone.0316546

Wallin Kihlberg, I., Florin, A. B., Efstathiadis, I., Brodin, T., & Hellström, G. 2024. Indications of reproductive disturbance by the invasive round goby on a native salmonid. Biological Invasions, 26 (2203-2215). https://doi.org/10.1007/s10530-024-03305-6

Bostedt, G., Carlén, O., Naddafi, R. & Florin, A.-B. 2025. Effects of the invasive round goby on Swedish recreational fishing values. Fisheries Ecology and Management. https://doi.org/10.1111/fme.70050. 

Arnet, Guillaume. 2021. Diet of perch in the Baltic Sea – could the European perch (Perca fluviatilis) be used to combat round goby (Neogobius melanostomus)? MSc thesis Lund university.

Blanco, Manuel. 2024. Food or food? Mitigating the spread of the invasive round goby (Neogobius melanostomus) in the Baltic Sea by exploring predation by native predators or targeted/directed fishing. MSc thesis Lund university.

Junehag, L. 2023. Hur skiljer sig passageaktivitet mellan stensimpa och svartmunnad smorbult i slitsrannor? Kandidatarbete i biologi. Sveriges lantbruksuniversitet.

Karlsson, Julia. 2023. Can native predators in the Baltic Sea limit the spread of invasive species? – Perch size selection of round goby. MSc thesis Lund university.