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An oil tanker goes under the Lions Gate Bridge at the mouth of Vancouver Harbour in this May, 2012, photo.JONATHAN HAYWARD/The Canadian Press

Proposed new oil pipelines have heightened concerns about major spills from increased tanker traffic on the West Coast, but a new study has found that fleets of leaking recreational boats and other small vessels are more likely to foul B.C. waters.

Stefania Bertazzon, a University of Calgary researcher, worked with several federal government departments and the University of Victoria in putting together what is thought to be the first study of its kind in the world.

"I think the main thing that came out is that it's not only the big tankers [causing spills]. There are other types of vessels and activities that contribute," said Dr. Bertazzon, who led a study that looked at three years of oil-spill data gathered by the federal government. "That was a bit of a surprise."

Dr. Bertazzon divided coastal waters into cells that were 25 kilometres square and then catalogued all the oil spills in each cell, as recorded by patrol flights in the National Aerial Surveillance Program.

More than 100 of the cells had at least one spill and many had multiple spills. "I think the highest one we have is a cell with 14 spills," she said. Dr. Bertazzon declined to give the exact location of that dirty patch of ocean, but said it was "in the general area" of Vancouver harbour.

The study looked at three regions – North Coast, Strait of Georgia and the Southwest Coast of Vancouver Island – and the biggest concentration of spills was in the Strait. "This region … has way more spills, so it's clearly the busy, busy part of the study area," Dr. Bertazzon said.

The study points to recreational boats, marinas, passenger ships and fishing boats as the causes of most spills, while cargo ships and oil tankers are responsible for a smaller portion. "I would like to stress that we are not saying [the big ships] aren't polluting," she said.

Dr. Bertazzon speculated that large tankers and cargo ships aren't as closely correlated with the spills because the study focused on near-shore waters, where the captains of big ships know they are being watched.

"Cargo ships and tankers are more heavily regulated than other types of vessels. They need to undergo port side inspection and we also believe they are aware of the surveillance overhead. They know about the airplanes," she said.

Dr. Bertazzon said marinas for small vessels are big contributors of spills. "There are all the old boats [at docks] that are leaking constantly; there are glitches in the way people fill up their boats. Most of it is carelessness. The marina is actually a place where a lot of [oily] discharge is generated."

Dr. Bertazzon warned that multiple recreational boat spills can, over time, be more damaging than a single big spill from a tanker.

"We know these sort of long-term continual spills have a greater impact on the environment than the big catastrophic spills that catch everyone's attention when they happen," she said.

Christianne Wilhelmson, executive director of the Georgia Strait Alliance, said her group has long tried to address the problem through "green boater" educational programs.

"In the 14 years we've been running the program we've seen things getting better," she said. "There's a dramatic change amongst recreational boat users in wanting to have a more positive impact." But Ms. Wilhelmson said the study shows recreational boaters have to do a better job.

Jeff Booth, commander of the Vancouver Power and Sail Squadron, said his organization strives to educate boaters about the risk of spills.

"The environmental impact of recreational boating is of great concern to us," he said. "One drop of oil or gas causes a significant amount of damage to the marine environment."