Round goby (Neogobius melanostomus) fishery in Latvian coastal waters

This case study focuses on the Latvian coastal fishery for the round goby (Neogobius melanostomus), an invasive fish species originating from the Ponto-Caspian region. Round goby was first observed in the Baltic Sea in the Gulf of Gdansk in 1990, and it now occurs throughout the Baltic Sea, except in the most northeasterly parts where it is considered too cold for the species to thrive. The species’ presence and distribution in the Baltic is most likely a result of repeated introductions to ports via ballast water in ships, following which it has spread from these sites via secondary dispersal.
The round goby fishery in Latvia is a small-scale coastal fishery that occurs during spring and early summer, mainly with specialized round goby gillnets and round goby trap-nets. Round goby appeared in the commercial fishery logbook for the first time in 2006, and in the following years catches increased, peaking at 1 113 tonnes in 2018. Catch rates then began to fall. Stock assessments indicate that the size of the round goby population in Latvian coastal waters has mainly been affected by high fishing pressure. The most rapid rise in the number of juvenile fish was observed from 2013 to 2014. This period ensured a rich increase in fish of suitable size for the fishery for the following years. After 2018 fishing mortality increased by 600 percent, mainly driven by emerging market opportunities and increased fishing effort. As a result, the population size decreased by half – after which it was no longer able to recover to the same abundance, and catches have declined. However, catch rates are still considered to be high and round goby remains a very important target species for local fishers: in recent years, round goby has become the second most fished species by total landings after herring in the Latvian coastal fishery. A positive effect of the round goby fishery is thus the additional income possibilities it creates for local fishers, especially at a time when the Eastern Baltic cod population is on the verge of collapse, and the abundance of many other locally important species is decreasing.
There is as yet no dedicated monitoring programme for round goby, and abundance data is only available for areas where it is commercially exploited, like Latvia. This is despite the fact that there are ecological impacts linked to the abundance of the species: scientific studies have revealed that round goby has negative impacts on flatfish recruitment, and it also has the capacity to alter the benthic macrofauna community through predation (van Deurs et al., 2021). There is no comprehensive monitoring for RG in the Baltic Sea, but it is clear that such a programme is needed. A monitoring strategy will not result in the conservation of the RG population size. The best period to monitor RG is in coastal areas during the spring using “Nordic nets”, based on inter-calibrating historical data sets and commercial fisheries landings. This combination makes it easier to catch specimens (Kruze et al., 2023).