The first reports of oiled seabirds in the Change Islands and Fogo Island area came in March 31, coast guard spokesman Robert Grant said Wednesday.
Since then, the coast guard and Transport Canada have conducted numerous surveillance flights, with crews spotting small, sporadic slicks during five flights.
"We haven't seen any huge volumes of oil," he added. "It's like sporadic sheening."
Grant, a senior response officer based in St. John's, said some samples have been collected and sent off to a lab for analysis.
The source of the oil remains a mystery, but Grant said it appears to be coming from an area west of Change Islands.
An environmental response team was sent to the area on Wednesday and they will use noisemakers to scare away flocks of birds, he said. A shoreline assessment is scheduled to start Thursday.
At one point, local residents reported seeing up to 400 oiled seabirds, Grant said.
Liberal Randy Edmunds, the provincial party's environment critic, says a slick was also spotted off Bacalhao Island, an ecologically sensitive area frequented by seabirds.
Edmunds said he's concerned the slicks may have an impact on the rich fishing grounds in the area.