Anyone who knows me knows that I can become very excited about identifying local birds of prey. While a cormorant may not be an obvious bird of prey, they are unique hunters... (Read more below.)
Firstly, cormorants can dive for fish by using their incredibly powerful eyes to fixate on objects underwater. In fact, they have one of the largest accommodation ranges in nature. This means that they can change the focal length of their eyes much more than any other animal. For example, when humans spot something and try to focus on the object, they can only change the refractive power of their eyes by 16 diopters. However, when a cormorant plunges into the ocean to catch a fish, it can change the refractive power of its eyes by about 45 diopters.
Additionally, their bodies are made for hunting. While their shape and webbed feet assist with diving, their feathers contain less oil than most water birds. For this reason, you will often spot a cormorant standing on a sunny dock or branch with its wings outstretched -- drying them off. Since their wings become soaked, you would think that this would hinder their ability to fly and hunt. However, it is believed that the water weight has the opposite effect and actually helps them dive deeper and stay underwater without floating upwards.
Cormorants can dive as deep as 45 meters and can live over 20 years.
Posts are a combination of my own research, visits, and conversations, plus various information found around the web. I try to provide sources, but if you have specific questions, feel free to ask!