Marine Mammals

I have a little bit of knowledge about marine mammals. Most of my knowledge is pretty basic because I haven’t researched much about them before. I often watch Discovery channel, especially shark week. (even though they aren’t mammals) I really only know the basics of marine mammals behaviors. They care and nurse for their young. Most travel in pods or groups. They have the same basic bone structure as humans, especially in their limbs. They have a way of communicating for survival purposes. Most have similar brain structure to humans as well.
I think that I may want to limit my research to just one type of marine mammal though. I think that if I try to compare all mammals I will be overwhelmed with information. I’m not really sure which mammal I would want to choice, because even within one species there are still a lot of different breeds. I think if I had to choice which animal it would be either the whale or the dolphin. However, should I choice another subgroup like humpbacks, or bottlenose dolphins to limit my search? Or can I compare them?
I have done a little bit of research on my own lately, and have found a few sites that would be good for comparing them. They actually have recordings of the different sounds that certain mammals make while communicating. I think that this could be very helpful when I start writing because I can actually hear what they sound like instead of interpreting or trusting what other people have said about the sounds they make.
I am pretty excited about researching this project. There is a lot of information about this, and I think that it will keep me interested in the topic.