Most of the research I've seen was done in Europe. I haven't seen any research done on the east coast of Canada.
Many places in Scotland and England have programs where they cull cormorants on an annual basis. You have to do it in an organized fashion. You decide the maximum population that a river can sustain, and every year you reduce the number to that.
But no, with regard to stomach contents, I'm not aware of that being done in Canada.