The fish are also smaller in size, according to the study done mainly by federal scientists.
And under current conditions, the scientists estimate either negative or two per cent growth in eight of 12 stocks studied.
Their findings, in an article in the Canadian Journal of Fisheries and Aquatic Sciences, rank natural mortality ahead of fishing activity as the main reason the northwest Atlantic cod stocks have not rebounded.
The study says, however, that directed and bycatch fisheries are still important factors in the cod's failure to recover.
The study suggests that if fishing activity stopped altogether, growth of most of the stocks could be in the 5-to-10-per-cent range instead of the current rate of less than 2 per cent.
