Another similar species, the Round Goby (Neogobius melanostomus), has already established large non-native populations in the Baltic Sea, and the newly discovered Eastern Tubenose Goby variety is likely to do the same.

Both species are considered invasive and pose a threat to native aquatic life.

Estonian researchers headed to the Finnish coast to learn more about the distribution of the Eastern Tubenose Goby. Despite its small size and harmless appearance, it requires close monitoring.

Katarina Kurina tells ERR's Novaator about her research on the species' naturalization.

Where was the first Estonian specimen found?

The first discovery was made near Sillamäe harbour [Narva Bay] in autumn 2020. However, monitoring catches from last autumn show that it is present throughout the Narva Bay area in northern Estonia, including west of Sillamäe.

How did the Eastern Tubenose Goby make its way to Estonia?

The species has been transported to Estonia via ship's ballast water. It is categorized as an alien species since it could not have swum here on its own. The fact that it has arrived in ballast water also explained its uneven distribution: it is present at some locations and not others. Also, it seems that the species is only found in areas where water from ships has been drained out and not elsewhere.

The Ponto-Caspian basin, which includes the Black Sea, Sea of Azov and Caspian Sea, is the ancestral home of the Gobiidae family. In 2006, this genus of fish has reached the Volga River Basin, the Rybinsky Reservoir in Russia, and the Bay of Neeva through the Neeva River.

The fish discovered in both the Rybinsky reservoir and Neeva bay are believed to be a distinct species within the same family - Proterorhinus marmoratus. Since DNA studies conducted by researchers at the University of Tartu revealed that discovered in Estonia fish is the Eastern Tubenose Goby and, in all likelihood, it arrived here from Neva Bay, it is possible that the Russian Tubenose Goby is also of the eastern variety.

Does this mean that the species cannot be identified from a photo?

Proterorhinus species are difficult to distinguish by morphological
data alone. In the Gobiidae family there is currently significant systematic confusion, which may be clarified in the near future, but right now I would be skeptical about any determinate conclusion that it's this species and not another.

That is, their appearance is deceptive: while there are typical differences between species, the coincides between then such as in size and in number of fins are unreliable characteristics. However, DNA analysis helps to tell them apart.

What is the state of Finland's southern shore?

At the beginning of June, we sailed down the Finnish coast. The goal was to determine the species' range as the Estonian Marine Institute (TÜ Eesti Mereinstituud) is the only organization conducting extensive research on this alien species in the Gulf of Finland. Finnish colleagues stepped in and assisted us in conversing with the locals, allowing us to catch the fish.

To catch them, you have to drag a noose - a fishing gillnet - from the shore into the sea and back. All fish caught in the net, as well as other information such as haul length and depth, water temperature, and so on, must be recorded as well. The other species in the net are also important because they help determine whether the habitat is suitable for the eastern tubenose goby. For example, if a Cottus gobio, bullhead, is caught in a net, it is reasonable to assume that the area is also suitable for the eastern tubenose goby, as their habitats are similar.

Although the species is not found as far west along the Finnish coast as it is here, we believe it has established itself there as well. The first sighting in Finland occurred in Helsinki, where a specimen was caught during a fishing tournament. Our catches, however, revealed that the species may be found as far east as Pohjoisselkä in southern Finland.

Do local fish have to be afraid of this newcomer?

For the time being, no definitive answers can be given; the coming years will provide clarity. Given that the Eastern Tubenose Goby is smaller than the round goby - it does not usually grow more than 10 centimeters long - does not feed on other fish, and is less aggressive, it can be anticipated, or hoped, that the species will not pose a serious threat on par with the round goby [which is considered as one of the top invasive species in the Baltic Sea]. This suggests that the risk may not be as great, but such assumptions should not be taken for granted in the case of alien species and we should keep an eye on the situation.

The level of competition between this species, the round goby, and our native fish has to be further studied.

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