The big question is: Are there sharks in Portugal?
Yes, there are. But they do not come ashore.
They cross Portuguese waters but do not get close to the coast because Portugal is not a destination itself for them, rather is a passing-trough point on the way towards reproduction and hunting spots such as the Mediterranean and the Nordic Sea.
According to the Florida Museum of National History the European countries were the highest number of attacks was registered are Italy and Greece.
On the contrary , Portugal has 0 (ZERO!) shark attacks.
However in general shark attacks are pretty low.
Here you can read "12 Things More Likely To Kill You Than A Shark" for example.
∆ So have a lovely swim in the ocean and enjoy Portugal! ∆