Video report by Rachel Bullock
A retired marine biologist on Teesside believes dredging of the River Tees could be the reason why thousands of dead crabs have washed up on the North East coastline.
Dredging is the process of excavating river or sea beds of debris and David McCready says he is certain this is what has killed thousands of shellfish, leading them to wash up on beaches across the region and North Yorkshire.
Mr McCready said: "There'll be a huge gash in the seabed but there'll also be a huge mound and I asked at the time 'did you dump it in a landfill?' and I didn't get an answer but I found out that they actually went about three miles off (the coast) to a spoil zone and dumped it where they dumped the normal channel dredges.
"That is right in the catchment area of our longshore current, taking it south."
In a recent meeting with DEFRA, the department overseeing the investigation, Mr McCready asked for samples to be sent to the government science lab, Porton Down but was told it couldn't carry out the necessary tests.
The Department for the Environment, Food and Rural Affairs said it had ruled out dredging as the cause, telling ITV News Tyne Tees that samples of dredge material must meet the highest standards to protect marine life. DEFRA also said that testing across the Inner Tees and the Tees estuary took place last April and found no evidence of contaminants.
In addition, tests by the Environment Agency also ruled out chemical pollutants as the cause.
In a statement, a Defra spokesperson said: “Sediment testing has ruled out dredging as a likely cause of the dead crabs and lobsters.
“Our priority is to understand the cause of the issue and investigations are ongoing.”
Mr McCready is calling for more samples to be taken and sent to independent laboratories for testing.
The former marine biologist added: "I would suggest that you send fresh samples from this area and send them to an independent lab."
Concerns have also been raised recently by fishermen in Whitby who say the mystery is starting to affect their business, with fishing pots often empty, something which Mr McCready thinks will continue for some time to come.
"The reason why there is nothing washing up at the moment in this last spring tide this week is because there is nothing there to wash up. They're dead", said Mr McCready.
"I was at a meeting last week in Whitby with the pot fishermen and one of the fishermen pulled 1,800 pots and there were three dead small velvet swimming crabs."