Scientists and fishermen have known for a long time that cod prefer certain areas of the ocean over others.
But what scientists are beginning to document is the extent to which the same cod return to the same area to spawn year after year, the way salmon and river herring return to specific water bodies, and how critical protecting those areas may be to the success of rebuilding those fish stocks to healthy levels.
"The whole field is now moving towards that (theory)," said Mike Armstrong, the assistant director of the state Division of Marine Fisheries. "The sad part is, we probably have lost 50 percent (of the distinct spawning populations)."
Good "cod bottom" doesn't have to be as massive as Georges Bank. It can be as small as a slightly raised plateau, covered in pebbles and small rocks, that offers food and shelter from predators.
Successful fishing is all about finding the fish, and good fishermen know where fish are at certain times of the year. With modern technology such as the Global Positioning System, which uses satellites to pinpoint fishing spots, it's possible to home in when fish are most vulnerable as they group together to reproduce.
"If these are distinct spawning groups … an unfettered fishery can wipe the whole thing out," Armstrong said. And once a group has been lost, there's a much slimmer chance of recolonizing it with random roving fish that don't have the fidelity to the area, he said.
If that is the case, it could mean that bringing back cod stocks to healthy levels is a lot more complicated than placing limits on the catch. The operating theory in New England fishery management has been to build a big mass of fish, hoping they will spread out in search of food and repopulate the areas that were wiped out by overfishing.