The world's largest animal is also one of its most vulnerable.

At 33 metres in length, the blue whale is dwarfed only by the ocean in which it swims. In the words of broadcaster and naturalist David Attenborough, "its tongue weighs as much as an elephant, its heart is the size of a car and some of its blood vessels are so wide, you could swim down them."

Until hunting of this animal was prohibited by the International Whaling Commission in 1966, it's estimated 1,700-2,000 blue whales were killed from their northwest Atlantic population, the same population that frequents Canada's east coast, Greenland and the Gulf of St Lawrence.

Its population before commercial whaling began in the late 1800s is unknown. However, updated figures from 2013, provided by the Canadian Department of Fisheries and Oceans (DFO), estimate there are fewer than 250 sexually mature individuals left.

This population made the endangered species list in 2005 under the Canadian Species at Risk Act (SARA), which entitles the blue whale to have its critical habitat protected. SARA committed to identifying this habitat by the end of 2014, but they recently cast doubt on that deadline.

"It's hard to make any promises," said Nicole Bouchard, Quebec regional manager with Species at Risk. As she explained, the gears of government turn slowly. "We're still aiming for the end of 2014."

Like the nomadic hunters of old, the blue whale follows its prey. Anywhere from 20-105 blue whales are observed in the Gulf of St Lawrence every year, stalking the 8 tonnes of krill they each consume daily. According to a report published by the Department of Fisheries and Oceans in 2010, the Laurentian Channel inside the Gulf houses the North Atlantic's largest known concentration of krill, making it a vital feeding ground for the blue whale and other endangered species, such as the right, bottlenose and gray whales.

This is the domain of the whales, its waters and krill spoken for.

Also residing in the Laurentian Channel is the Old Harry prospect, 80 km off Newfoundland's west coast and 460 metres underwater. According to the Halifax-based oil and gas company Corridor Resources, Old Harry could contain commercial volumes of crude oil...and they've secured an exploratory license to take a look.

"Corridor plans to drill an exploratory well at Old Harry in 2015 or 2016," said Corridor executive assistant Kathryn Patterson.

Corridor submitted an environmental assessment (EA) for their project to the Canada - Newfoundland and Labrador Offshore Petroleum Board (C-NLOPB) in 2011, which still hasn't passed review. Until it does, Corridor can't drill. This EA has been heavily criticised by the DFO and Environment Canada for being too optimistic in projecting oil spills at Old Harry. In spite of these criticisms, Corridor has stood by its projections.

"Corridor is confident that its Old Harry exploratory program will have no significant adverse environment impacts in the Gulf of St Lawrence," said Patterson.

She referenced a strategic environmental assessment published in April, 2014 by the consulting group AMEC Environment & Infrastructure, which concluded petroleum exploration activities can be undertaken in the Gulf as long as appropriate mitigation measures are in place. This assessment said major oil spills are "possible" but "unlikely."

However, minor oil spills are more common. In late 2013 over 6,000 litres of crude oil were spilled into the Atlantic Ocean from the Hibernia platform and in 2008, 4,470 litres were spilled from the SeaRose production vessel, both located on the Grand Banks of Newfoundland. These were preceded by a major spill of 165,000 litres in 2004 from the Terra Nova production vessel in the same region.

Between 1997 and 2013, over 180,000 litres of crude oil have been spilled off Newfoundland's east coast, roughly equivalent to 1,100 barrels of oil.

The fate of the blue whale might hang in the balance as the debate over oil spills rages on. According to a recovery strategy published by the DFO in 2009, fumes from oil spills can severely harm the blue whale's eyes, mouth and lungs; ingesting oil either directly or by eating contaminated krill could cause gastro-intestinal and pulmonary intoxication, and possibly feeding problems.

"The exploitation of oil and gas along the Northwest Atlantic coasts and in the Gulf of St Lawrence...represents an additional risk for pollution," the strategy said. "Toxic spills are therefore a potential threat that cannot be ignored."

Mary Gorman, with the Save Our Seas and Shores Coalition, said if Old Harry is drilled, it's only a matter of time before oil hits the Gulf.

"A major oil spill is not only likely but inevitable if this development proceeds," said Gorman."According to eco-toxicology scientists, it will be virtually impossible to clean up an oil spill in the Gulf of St Lawrence, especially under winter ice."

Gorman said water in the Gulf of St Lawrence only empties into the Atlantic Ocean once a year, meaning oil spilled at Old Harry wouldn't be out of sight - out of mind any time soon.

A study published earlier this year by the Université du Québec à Rimousk and the University of Waterloo, suggests oil spilled at Old Harry would coat Newfoundland's southern shore and possibly Cape Breton Island and the Magdalen Islands. If the spill was large enough, much of the Gulf could be severally impacted.

But perhaps the greatest threats to the blue whale's recovery lie not with the near future of exploratory drilling at Old Harry, but with the more distant commercial drilling.

Two seismic surveys have already been completed at Old Harry and more would be needed if they strike oil. According to the C-NLOPB, more wells would be drilled just to determine the size of the oil field, for which seismic testing would again be employed.

Lindy Weilgart, an associate professor at Dalhousie University, is an expert on underwater noise pollution and has written extensively about the impacts of seismic testing on marine life.

"Whales are dependent on sound for all vital aspects of their life," said Weilgart. "So introducing noise that masks or interferes with their signals is almost certain to impact them somehow."

Weilgart said deafness, even death, is possible for whales caught in regions of seismic testing, some species being more vulnerable than others. She can only speculate on the vulnerability of the blue whale because it's never been studied. However, she's confident seismic testing interferes with blue whale communication and food finding; it could also cause disorientation and behavioural changes in both the whales and their prey.

"Seismic surveys are mainly [in the low-frequency range], which is where blue whales communicate, so it must be assumed that there will be some negative consequences," said Weilgart. "Years ago, I would have assumed krill would not be as likely to be affected, but with recent research showing impacts on scallop larvae, affecting development and growth...I am not so sure anymore."

Of special note in the blue whale's 2009 recovery strategy are whale-to-ship collisions, which are fatal to whales in 70 per cent of cases. The strategy said at least 5 per cent of blue whales in the Gulf bear scars from such collisions.

"Blue whale mortalities related to collisions with vessels have been reported in various oceans," said the recovery strategy. "Even though there have not been many cases reported in the Northwest Atlantic, the number of St. Lawrence blue whales with scars from collisions indicates that this threat is real and likely significant. It is possible that whales struck and killed by fast moving vessels sink to the bottom without being detected, leading to an underestimate of the real impact of this threat."

A spokesperson with the C-NLOPB said an exploratory well at Old Harry wouldn't involve more than two vessels to transport personnel and equipment to and from the drill site. However, oil tankers would be employed if commercial oil production ever took place in the Gulf.

Given the controversy surrounding Old Harry, the C-NLOPB has committed to "extensive public consultation" before completing their review of Corridor's environmental assessment. They have no timeline in place for this public consultation, but the spokesperson said consultation will not happen this summer.

And so the stage is set for important decisions affecting the Gulf of St Lawrence, as two irreconcilable goals meet at Old Harry - establishing the first major oil and gas operation in the Gulf...and the survival of the largest animal ever to call our waters home.

Zack Metcalfe works on the Blue Whale Campaign which aims to raise public awareness of the dangers posed by fossil fuel development in the Gulf

See also:

First Nations say no to oil exploration in the Gulf of St.Lawrence

Hunt for oil in the Gulf of St Lawrence intensifies

Offshore seismic testing puts wildlife at risk, biologist fears