However, to do that my aperture was around f3.5 or f5.6. If shooting for prints, when you take the film to your lab ask them to print for the whale, not the surrounding water. If not told, labs will usually print your pictures so that the water looks right, but the whales are just black silhouettes. If you forget to tell them and this happens, all is not lost. Take the negatives and prints back and ask them to print again, this time for the whales - not the water.
Whales can be challenging subjects when it comes to exposure.
Many parts of a humpback, for example, are jet black while the flippers are almost pure white. Such extremes in the same shot call for a low-contrast film. If you have them, your monster 400 or 600mm lenses may not be the first choice. They are difficult to hand hold and have a very shallow depth of field. More practical is a zoom, in the range of 75-300mm or so.