In recent years, the round goby (Neogobius melanostomus) has become a pressing problem in Baltic Sea waters, especially in the Latvian coastal area, posing challenges to local ecosystems.
The natural range of this small but highly adaptable fish is in the Azov, Black and Caspian Seas. Outside this area, the fish has spread mainly through ship ballast water and has gradually established distinct populations in both Europe and North America.
It was first recorded off the Latvian coast in 2004 near Liepaja and is now found along the entire Latvian coast. The first records of the species in freshwater have also been recorded, so the appearance of the round goby in freshwater in the lower reaches of large rivers in Latvia in the near future cannot be ruled out. The species spread rapidly and became a dominant component of many coastal habitats. The round goby is extremely tolerant of a wide range of environmental conditions, including good adaptation to environments with high levels of pollution. The round goby can be found in both marine and freshwater, but prefers brackish water ecosystems.
Negative impacts
Loreta Rozenfelde, a researcher at the Marine Unit of the BIOR Institute for Food Safety, Animal Health and the Environment, explains why it is important to limit the distribution of this species: "The round goby is an aggressive and territorial fish that competes with native Latvian coastal fish species such as flounder and eelpout, thus reducing the number of available spawning grounds and food supply. As a result, this species may threaten coastal ecosystems and the functioning of existing food chains."
The round goby feeds mainly on various molluscs, such as northern mussels and Baltic flat mussels. These mussels are an important part of the Baltic Sea ecosystem, filtering the water. In recent years, the biomass of bivalve molluscs has been declining rapidly, as their rate of recruitment into the Baltic Sea ecosystem has not kept pace with the current consumption of bivalve molluscs. If this trend continues, eutrophication of the coastal ecosystem may increase and water quality may deteriorate.
However, from a fisheries point of view, the impact of the round goby is twofold. On the one hand, it creates competition for commercially important fish species, affecting their populations. On the other hand, it has become an important prey species for predatory fish species, improving their fatness. It should also be mentioned that the round goby has become an opportunity for local fishermen - an important coastal fishery. Currently, round goby is the second most fished species after herring and accounts for a large volume of exports to Ukraine and Bulgaria.
The current population of round goby is relatively large and stable, so it is no longer possible to eradicate this alien species from the local ecosystem. In the long term it will become an integral part of our local ichthyofauna. Therefore, various studies and monitoring programmes are being carried out in Latvian coastal waters to improve the understanding of the status of the species. It is worth mentioning that since 2022, BIOR Institute, in cooperation with coastal fishermen, has launched a large-scale study on the mapping of the round goby migration in Latvian coastal waters, within theLIFE REEFproject "Survey of marineprotected habitatsand identification of the necessary conservation status in the Latvian Exclusive Economic Zone". Over two years, a total of 8,000 round cormorants were tagged with T-bars or anchor tags. There is a possibility of catching a few more tagged individuals in the coming fishing seasons. Such long-term migration data are very valuable. "It is important to develop effective management strategies to reduce the impact of this invasive species on local ecosystems and improve the management of spatial fisheries. Similarly, public education oninvasive speciesis an essential step to increase public participation in controllinginvasive species," explains Loreta Rosenfelde.
Therefore, when fishermen or anglers catch round goby marked with a red sticker (the words "BIOR RIGA" and four numbers), please record the sticker code, the duration of fishing, the GPS coordinates of the place of capture and the date. Catches should be reported to the Institute's Marine Unit by phone +371 20239304 or by sending an e-mail to ivars.putnis@bior.lv.
How to identify the round goby?
The website www.invazivs.lv explains that the round goby is the largest species of gobies found in Latvia, with an average length of 15-20 cm. The round goby is a bottom-dwelling fish with a rounded body shape and a relatively large head with protruding eyes. One of the characteristic features of the species is a dark spot on the back of the first dorsal fin. The pelvic fins are disc-shaped and are fused together, facilitating anchoring to the bottom.
Males are characterised by a very dark, almost black colouration during spawning, although there are also small males which resemble females in appearance and colouration. Females retain a light yellowish body colour both during and after spawning.
The "Unwanted Invaders" awareness campaign also introduces other species such as the Chinese mitten crab, the American signal crayfish, the rattan and the spiny crayfish. To explain how to recognise theseinvasive species, where to find them and how to report them, a digital billboard has been placed in several Latvian cities since June. From mid-July, an information installation and an explanatory billboard will also be installed in several Latvian cities - Sigulda, Salacgrīva, Jelgava, Liepāja and elsewhere.
What to do if you spot a round goby?
There are several options to control its spread. Catching round goby by angling or specialised fishing is the most effective method to reduce the population of this species.
The fish can be eaten and in some regions round goby is considered a delicacy. It can be cooked in various ways, such as frying, stewing or in soups. The flesh of the round goby is pale. It is characterised by a mild and delicate flavour with no specific flavours. It is these characteristics that make it a safe choice for people who are just beginning to explore the world of seafood.
As this species is beginning to colonise fresh waters associated with the sea, reports of new records of the species in freshwater ecosystems are important. Sightings can be submitted in two ways - at www.invazivs.lv and via the Survey123 mobile app, which requires the installation of reporting forms before going out into the wild. Instructions on how to use the mobile app and set up the questionnaires are available at www.invazivs.lv.

Information prepared by Elina Junolainen, Olsen+Partners.

Photo: Gunta Gabrāne