Sometimes the regulations are difficult to understand, but basically, there's a limit on how many species of fish you can keep according to the rules set out by our province.
If you have a sports license, you can only keep in your possession of 5 salmon. If you have a conservation license, you can only have in your possession two salmon. Possession meaning having salmon on the stringer with you while you fish or stored in your freezer at home. For example, if you are fishing witha conservation license and you have two in your possession, you may not keep any more salmon, but you can only catch and release until you consume one of the salmon.
Regarding the situation with roe, that counts as part of your possession, since it's part of the salmon. Like I mentioned above, it doesn't matter if you keep one tiny roe or a bag full of roe from one salmon, it counts as ONE possession and is part of your limit. If you milk two different salmon, that counts as two possessions and if you have a conservation license, that's it—you cannot keep anymore salmon and are only allowed to catch and release.
The province has set out a guideline to follow on how much you can safely consume fish from Lake Ontario. Since you were fishing Bronte, the guide mentions that any fish over 26" is not safe to consume. We all know that it's against fishing regulations to leave a fish behind if it's fit for human consumption. So, if you land a hen over 26", gut it for roe, and leave it on the side, legally, you're not committing a crime since the fish is obviously not safe to consume. It's a double edged sword. Even if you do leave the fish behind to rot, you allow other animals to consume the fish and nutrients from the dying salmon can be absorbed by the trees around.
Even maggots that develop in the rotting salmon can be washed into the river system and feed the smaller fish.
It's an interesting cycle and I don't think there's any perfect right or wrong answer if you leave fish behind.