There is a great number of boat tours in Barcelona. You can choose an ocean liner, a pleasure boat or a yacht and visit Canaries, Ibiza, Tenerife, Majorca or some other places. By the way, the name of the islands is unrelated with the name of the bird at all. The translation is: "Dogs' Islands". Why dogs? It is difficult to say but maybe because of the dogfish.
If you are not interested in the islands, you can take a Barcelona boat tour along the coast of Spain, and enter little ports, and eat marine food there. There are a lot of fisherman villages along the coast so you won't have to travel much. One or two hour boating is a popular and not expensive activity. Yachts are for those who have a little more money. You can also try an ocean fishing there; it is a real chance to catch a really big fish. You can try different variants, such as leger rig or jig. You can also do diving, or just swim in clear warm ocean water, or just spend a marvelous romantic evening drinking champaign and watching the dawn and beautiful Barcelona landscapes.