Whales (Cetacea) are the only mammals that have adapted to living in the water. There are more than 80 species, and some inhabit rivers. There are two suborders: toothed whales (Odontoceti) and baleen whales (Mysticeti). They evolved from terrestrial animals and during evolution significantly adjusted to life in the water. They don't have back limbs, and front limbs are transformed in fins, spine is extended into muscle caudal fin. They adapted breathing to be able to dive longer and they are using echolocation for navigation and locating their pray. Also reproduction is adapted to three-dimensional space in which they live. Cetacean ecology describes the relationships between cetaceans and their physical and biological enviroment, including their interactions with their pray and predators. In past thay were endangered because of overfishing whales, but today are many species recovered due to regulations by International Whaling Commission (IWC), whose member is the Republic of Croatia since 2007. Adriatic Sea inhabits one species of cetaceans – common bottlenose dolphin (Tursiops truncatus), but it is frequently visited by other cetacean species. Dolphins are the endangered species because of drowning in the fishing nets, but also because of enviromental pollution, boat noises and climate changes. Dolphins are monitored around Cres Island and Lošinj Island. This archipelago is suposed to be declared a special reservation. In that way, Croatia would fulfill part of it's obligations to the ACCOBAMS agreement signed in the 1996. Cetaceans are an important part of the ecosystem and it is important to introduce their lifes to protect them.