Wageningen University is starting a new four-year investigation into the decline of lobsters and mussels in the Oosterschelde estuary south of Rotterdam.

An earlier investigation to see if the lobster population is being affected by steel slag, a byproduct of steel manufacturing used to strengthen coastal defence works, was inconclusive.

Lobsters from the Oosterschelde which had been exposed to steel slag did not show any significant differences compared to lobsters living in the Grevelingenmeer lake where no steel slag has been used. An investigation into the presence of bacteria, parasites and toxic substances did not yield any results either.

“We thought we would at least find some sort of pathogen. Some lobsters got better, so that must have meant they had a disease. But what that was we have no idea,” researcher Jildou Schotanus told broadcaster NOS.

The new project will also try to find an explanation for the mass decline of mussels in the Oosterschelde. “From 2016 there have been years when the mussels die off in great numbers, such as this year,” Schotanus said.

The research will include a count of the lobsters in the Oosterschelde, put by local fishermen at 10% of what it was.

“We will see if that is the case and if the population is growing again. We will look at changes that have taken place in the last decade, including in water quality, climate, the composition of algae and human activity. We will also have another look at parasites and viruses that may play a role,” Schotanus said.

The investigation will start in January.