Massive mortality of Oosterschelde lobster remains a mystery, WUR will conduct further research

• Tessa Neijland

  editor Domestic

Things are still going badly for the lobsters in the Oosterschelde. Due to mass mortality, their numbers have drastically decreased this year. Lobsters caught alive during the lobster season (from March to July) were often weakened and limp.

Research by Wageningen University & Research (WUR) into the cause has yielded nothing. That is why research will be conducted again from January. This new research also includes mass mussel mortality.

“From 2016 onwards, there are also years when mussels in the Oosterschelde die in large numbers,” says WUR researcher Jildou Schotanus. “Some years they do well, other years they don’t. This year was a bad mussel year.” Whether there is a connection with the mortality of the lobsters, and if so: what the connection is, must also become clear from the new research.

Nature organizations and lobster fishermen in the area believe that steel snails cause massive lobster deaths. Steel slag is a residual product from the steel industry, in the Netherlands mainly from Tata Steel. In the Oosterschelde and Westerschelde, among others, the gray stones are used in coastal reinforcement projects.

Tata Steel calls steel slag a certified by-product that is not harmful to nature, if applied properly. However, there have been concerns about the use of steel slag for some time. Last year, a study by the National Institute for Public Health and the Environment (RIVM) showed that steel slag may be more harmful than thought. The Human Environment and Transport Inspectorate (ILT) was also involved ring the bell.

To investigate whether steel snails indeed influence the health of lobsters, living lobsters from the Oosterschelde were compared with lobsters from the Grevelingenmeer, where steel snails are not used. “We were unable to find any significant differences,” says Schotanus. “So steel slag does not appear to be a cause of mortality.” An extensive investigation into pathogens such as bacteria and parasites also turned up nothing, and the same applies to an investigation into toxins.

That was quite unexpected, says Schotanus. “We thought we would find something of a pathogen. Some lobsters also got ‘better’ again, which seems to indicate that they had a certain disease. But what it was remains a mystery.”

The new research will be a lot more thorough than this year’s research. This shows how many lobsters there are still in the Oosterschelde. “Fishermen are talking about a mortality of up to 90 percent this year, but research will show whether that is correct. We will also investigate whether the population is increasing again.”

“We first map out what has changed or could have changed over the past ten years. Consider water quality, climate, algae composition or human activity in the water.” The search will also continue for bacteria, viruses or parasites that make the mussels and lobsters sick.

The research starts in January and will last four years.