That is at the extreme south of the salmon range, there were a couple of rivers in the north of Portugal which did contain salmon, but not sure of their current status. The northern western part of Spain would give you a better chance of a salmon.
Rivers Minho and Lima but the season only lasts from 1st March until 31st July. There is a bit of information on Google which indicates they fish mainly from boats amongst all the canoeists and other watersporters. I'd suggest Spain would be a much better bet.
River Miño is shared between Portugal and Spain. Spanish part is Galicia. There is a beat "Frieira" where annual limit is 5 salmon per season. But the best river in Galicia (west coast of Spain) is River Ulla, wiht a limit of 35 for 3 beats. There are good rivers at North coast too. Foreigner angler can fish with a special rod license, only for about 4 euro per 15 days plus a day ticket. Season ends 15th July to 15th August depending on the river. Tight lines if you come here.