Whales and dolphins are wild creatures. They have the whole ocean to play in so no guarentee that they will be seen.
If you have several martinis, a few tequilas and several bottles of wine you would be more likely to see whales and dolphins in the Bay of Biscay.
I have sailes through the bay of buscay,and saw many dolphins and marine life,
Wales have also been spoted although I havnt seen one myself.P&o ferries run a four day mini cruises across Bilbao wich passes through the bay of biscay and the staff aboard lets you know when to look out forthe marie life,I found it very good.