Sick and Dead Fish: Overview

Dead eelpout (Zoarces viviparus). Storsanden, Nörskäret, Finland. Baltic Coastal Expedition. July 2013.

An Unexplained Problem in the Baltic Sea- a number of fish in poor condition

Oceana has conducted several at-sea expeditions worldwide with the aim of gathering biological data for the basis of increasing available knowledge, proposing new Marine Protected Areas and management measures. Since the startup of our Baltic Sea office we have conducted three expeditions in the Baltic Sea and the Kattegat between 2011 and 2013, using a Remotely Operated underwater Vehicle (ROV), divers and Van Veen grab to document important species and habitats.

Dead three-spined stickeback (Gasterosteus aculeatus). Puck Bay, Hel Peninsula area, Poland.Compared to expeditions conducted in other parts of the world, we have encountered a particularly high amount of dead fish and fish that appear to be abnormal, in poor condition or sick. We don’t know what the reason for this is, and it is not easy to pinpoint a specific cause. There are multiple factors that could be responsible, which makes this problem even more difficult to solve. Natural causes of death cannot be ruled out, such as infection or disease or the factors caused by specific Baltic Sea hydrography. It could be a result of the poor environmental status of the Baltic Sea, or simply because the decomposition rate is slow due to the fact that there is very little marine life in the Baltic Sea compared to other seas. However, we do believe this matter needs to be investigated, as these incidents are occurring all over the Baltic Sea.

 

Every now and then these types of findings are also discussed in the news, with incidents popping up in different parts of the Baltic Sea.

In Sweden, reports by local authorities, inhabitants and fishermen on bad water quality, sick and wounded fish, and fish disappearing from the coast, have been particularly high in the area of Hanö Bay, in the Southern Baltic Sea. In 2013 the Swedish government therefore commissioned the Swedish Agency for Marine and Water Management to investigate possible sources to the problems. Water quality, hazardous substances, fish and fisheries, ecosystem and food web effects were investigated. The investigation could not determine the cause of the reported problems, although contamination and lack of food supply have been mentioned as possible causes, so further monitoring and investigations have therefore been commissioned.

Three-spined stickleback (Gasterosteus aculeatus) dying. Storsanden, Nörskäret, Finland.

In Denmark, diminishing local fish stocks have been reported and the Danish Technical University has carried out an investigation to try and determine the cause. Oxygen depletion and local contamination have been mentioned as possible causes.

In Germany there have been reports of dead fish washing up on shores, as well as on increasing occurrences of dead flatfish, but this has not been verified by the authorities.

In Finland, a number of dead fish were observed close to a river mouth in the Bothnian Sea. This was most probably due to a lack of oxygen.  

 

In addition to this fishermen and scientists are reporting that cod and other fish species in the Baltic Sea are getting slimmer and weaker, with a decreasing mean body weight. 

As difficult as it may be to find an explanation for the high numbers of dead and sick fish in the Baltic Sea, we still think that this issue requires further investigation. Information needs to be compiled on this matter, in order to draw a better picture of this at the Baltic Sea level.

Oceana would be interested to know if you have experienced anything similar in your area. So, if you have witnessed sick and dead fish in the Baltic Sea, please send an email with further information to [email protected] and we will add the information to the online map/ interactive tool. Hopefully this effort will contribute to a better overview and understanding of the environmental challenges in the Baltic Sea.


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Dead & sick fish found at Oceana dives in the Baltic Sea from Oceana on Vimeo.