Tests haven't pinpointed what killed herring in Digby County
Thousands of dead and weakened fish started rolling in with the tide in late November
Scientists have ruled out several possible causes for the deaths of thousands of dead herring that washed up on beaches in Nova Scotia's Digby County this fall, but still haven't yet pinpointed what killed the fish.
The dead and weakened fish started rolling in with the tide in late November in St. Marys Bay and the Annapolis Basin.
Researchers examined the tissues of the fish and performed bacteriology and virology tests on the carcasses. To date, all have turned up nothing.
One concern was the herring could have been infected with viral haemorrhagic septicaemia virus, a disease that prompted bans on the export of fish products when it was detected in other areas.
"That was an illness that was on a lot of people's minds," said David Whorley, the Department of Fisheries and Oceans's area director for southwest Nova Scotia.
He said it was detected in Newfoundland three months ago, but tests for it in Nova Scotia have come up negative.
Whorley said the department is still waiting for some tests to come back. Algae toxins normally associated with shellfish are also being investigated.
Provincial and federal fisheries experts, along with the Canadian Food Inspection Agency, the Atlantic Veterinary College in Charlottetown and an independent laboratory, are working to figure out the mystery.
Fish farm involvement examined
DFO is warning people to only buy herring from licensed harvesters until they figure out why the fished died.
As the list of possible causes is checked off, others are being added, including the possibility of nearby fish farms being involved.
"We've looked into such things as infectious salmon anemia and so far there is no evidence of a link," said Whorley. "But the books aren't closed on all of this."
Aerial surveys done
Scientists also used an aircraft as part of the investigation too look at whether there was whale and herring interaction.
"This was to look into predation but there just isn't any evidence of that yet," said Whorley.
The public has been helping with the investigation but people don't need to collect any more samples, he said.