Value of the invasive round goby (Neogobius melanosomus) as prey for cod (Gadus morhua) (39542)

Project Details


The invasive round goby (Neogobius melanostomus) has rapidly spread throughout the Baltic Sea in the past two decades. Originating from the Ponto-Caspian region the round goby was first observed in the Baltic Sea in the Gulf of Gdansk, Poland, in the early 1990s. The first reports on round goby in Scandinavia occurred in Finland 2005 and in Sweden and Denmark less than 10 years ago when the fish was observed in coastal waters of Bornholm and the Swedish coast of Hanö Bay. Since then the number of round goby in Danish coastal waters has exploded concurrent with a rapid range expansion, especially around the southwestern and southeastern parts of Zealand, and into the belts and fjords around the islands south of Zealand. In recent years round goby has also been reported from several major Swedish port areas including Göteborg in Kattegat and Visby on the island of Gotland. 

Since round goby can tolerate marine, brackish and freshwater conditions, and has been observed in several Danish creeks, the fish is expected to spread rapidly along the Danish coastline and also into fjords and streams. Similarly, round goby has in past few years expanded its range northward, occupying currently also the Bothnian Bay. In Finland, it is increasing rapidly in the coastal areas both in terms of abundance and range and in Baltic waters round goby is rapidly becoming a nuisance, and in certain locations it even is the dominant species in commercial catches. In some locations in Poland the Danish Smålandsfarvandet the round goby now totally dominates the coastal fish fauna and it is also targeted by recreational fishery.

The species role as a predator has been locally fairly well studied during recent years, but less is known about its potential importance as a prey item for native predators such as piscivorous fish and birds. Local studies have shown that the round gobies experience predation from at least cod, perch, cormorants and grey herons. However, little is known about their nutritional value as compared with the predators’ typical prey species.

The role of the round goby for cod is especially interesting due to economic importance of cod in the Baltic Sea. Cod occurs in the whole area but reproduction is limited to the more saline parts. The Eastern Baltic cod makes up the majority of cod in the Baltic Sea and the stock drastically declined in the 1980s. This has been in part due to overfishing but it has also been negatively affected by degradation of spawning areas due to oxygen depletion in the deeper water in the eastern part of the Baltic Sea. Fishing is now being managed in the EU management plans, first adopted in 2007 and a new adopted in April 2016. Recently, however also a problem with extremely bad physical condition among the cod has been discovered that might jeopardize the recovery of the population. Reasons for the poor condition is hypothesized to be caused by spatial mismatch between cod and its main food items herring & sprat. The introduction of a new food item such as the round goby might then have a big impact on condition of cod.

Often, the impacts of invasive species are considered negative, but as an ample prey option for benthic cod, the impact of round goby may be locally considered positive for predators. Fishers have in some regions reported that the cod preying on round goby seem to be in better condition than the cod that are not. In addition, due to the interconnectivity of the aquatic habitat, management options on invasions are very limited. Predation by native species may provide natural resiliency, which can in turn provide some control over the invasion. Management of the natural resiliency may therefore be the best tool for managing aquatic invasions.

The objectives are (1) to investigate the nutritional value of the invasive round goby as prey for the economically valuable cod (Gadus morhua) and (2) to provide networking opportunities for students and PhD students involved in round goby research in Denmark, Sweden and Finland.

The project is funded by Nordic Council of Ministers. 

Research area: Fish Biology
Research area: Marine Living Resources
Effective start/end date01/05/201830/04/2019


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