HALIFAX - Schools of dead herring keep washing ashore along the rocky beaches of western Nova Scotia, prompting a retired scientist to enlist the help of local naturalists and bird watchers as he continues to gather data about the mysterious phenomenon.

Ted Leighton, an adjunct biology professor at Nova Scotia's University of Sainte-Anne, says he has compiled more than 40 sightings since tens of thousands of dead and dying fish started appearing in St. Marys Bay in late November.

Leighton says the latest sightings were reported Thursday in the Tusket River area, which is southeast of Yarmouth -- and he says more dead fish were spotted in St. Marys Bay and in the Annapolis Basin earlier this week.

On Wednesday, federal scientists said they had yet to determine what is causing the die-off, despite a battery of tests.

Fisheries and Oceans Canada says more tests are expected, including a check by the Canadian Food Inspection Agency for toxins caused by algae, and the possible presence of domoic acid -- a toxin sometimes found in shellfish.

Meanwhile, Leighton has posted a message on his Facebook page calling on all naturalists to report any sightings of dead herring to him, along with details about the approximate number of fish, their specific location, the length of shoreline affected and the presence of other dead fish, birds or mammals.