Years ago a Cod tagging program was conducted by the Gulf of Maine Research Institute. GMRI was funded by NOAA for this tagging program, the results of which are posted at http://www.codresearch.org
The results of the tagging program never quite made headlines, it’s unfortunate as the data is terrific and the website allows for easy analysis.
The map below shows locations of Cod caught in the Gulf of Maine and beyond. The name Cod is said to perhaps have originated from the Norse word “skride”. Have a look at this tagging program map and 
then understand that Skride in Norse is translated to mean, “Wandering”. So if you’re wondering at times where the Cod are or have gone to…remember that hundreds or perhaps thousands of years ago the Norse people knew that Cod moved around.
The tracking website allows you to follow a single Cod, I’ve done this and have noted some that stay local, some go to Georges Bank, some go north to Newfoundland. Interesting in view of their recent uptick in Cod, perhaps the populations are intermixed? There has been research to delineate populations which suggests that Cod stay local to areas- the tagging program seems to indicate a possible mixing of the populations. One has to wonder how many Cod are moving to distant grounds and where.
Given the recent quotas by NOAA demanding compliance with the The Magnuson–Stevens Fishery Conservation and Management Act (MFCMA) one would hope that additional research and tagging is planned.
Given the uncertainty in estimating a population an error on the side of conservation would seem in the best interest of all. The past overfishing has resulted in perhaps the best conservation efforts at any time. But don’t be so quick to blame the commercial fisherman. There is data to indicate that in some years the recreational catch is similar in size to the commercial catch. “Until the 1970’s, it was thought that commercial fisheries took the greater part of the total marine fishery catch in the waters of the United States. However, most species of fish in estuarine and inshore areas, as well as many in open waters, are harvested jointly by recreational and commercial fishermen. Catches by the marine recreational fishery are a significant portion of the total landings of many marine species. “ (NOAA Advisory https://www.st.nmfs.noaa.gov/st1/recreational/overview/overview.html )
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