There are estimates of how many salmon are killed by user groups - it is called estimating harvesting rates by sector, that is what DFO uses in part to decide upon their next year harvesting/allocation rates, and numerous fishing regulations that all user groups are expected to adhere by. This is what just DFO did to base their
early closure of the coast wide recreational halibut fishery. To say DFO doesn't do this would be to imply that they are not following standard fisheries management best practices
The feedlot salmon farm industry could also try to provide rough estimates of the number of salmon killed by large numbers of sea lice found around their net pens - BUT sympathetic DFO does not require it and I would image that hell would freeze over before the multi-national fish farm corporations would provide such data. Such data would be bad for the FF business and their corporate shareholders bank accounts!