A huge seal population is preventing cod stocks from rebounding off Nova Scotia, two former directors of science at the Bedford Institute of Oceanography say.

The work of Bob O'Boyle and Mike Sinclair backs what fishermen have argued for years.

"We conclude that indeed the seals are responsible for the lack of recovery of the cod," Sinclair told CBC News.

Sinclair retired as director of science at BIO in Dartmouth, N.S. He took over the job when O'Boyle left.

They decided to do their own study looking at the connection between cod and seals because they believe some other studies aren't accurate.

"Basically, we were not convinced that the studies that were out there really accurately reflected what was going on, so we thought we'd have a look at it ourselves," Sinclair said.

Commercial fishing of cod was banned on the Scotian Shelf in 1993, after decades of overfishing led to the collapse of cod stocks.  

The Sable Island seal population has spiked since the 1970s, climbing from about 3,000 to 300,000, a doubling of the population every seven years.

Sinclair and O'Boyle agree with other researchers that as the number of grey seals grows, the amount of fish consumed spikes too.

Seals eat one to two tonnes of fish every year, they say.

The two ex-directors said some studies focus too much on analyzing seal blubber and not enough on what's in a seal's stomach.

While some researchers say seals eat only small cod, Sinclair and O'Boyle found that seals eat medium and large cod too.

"What we are saying is given the size of the seal population, which we know is very large, you are not going to get a recovery," said O'Boyle.

Their study will appear in the March edition of Fisheries Research, though it's available online now.

Their findings support the arguments of fishermen, who have long blamed seals for preventing cod from springing back.

One study produced by the Canadian Science Advisory Secretariat suggested an experimental cull of 70 per cent of grey seals in the southern Gulf of St. Lawrence to determine whether cod stocks would recover.

The report, released last year, acknowledged that more research is needed.

It also concluded that a cull on Sable Island of 50,000 animals over five years would have little impact on the cod.