The most common reason for crumbly salmon patties is that they are too wet. They need a certain amount of bread crumbs or some other dry breading to hold them together. Since salmon types vary in the amount of fat and moisture, you may have to adjust your recipe. If you overmix your salmon, this can also make them too dense, and they can fall apart when cooking them. Try chilling your patties for 30 minutes before cooking and do not handle them too much.