Marine and aquatic mammals form a diverse group of 129 marine species and approximately 55 aquatic species that rely on the bodies of water for their existence. They include species such as cetaceans (whales, dolphins and porpoises), sirenia (manatees and dugongs) but also hippopotamus, beavers, shrews, capybara and seals as well as polar bears and sea otters.
Some species such as cetaceans and sirenians are fully aquatic while others such as seals and sea-lions are semiaquatic - spending the majority of their time in the water but returning to land for important activities such as mating, and breeding. Still others such as polar bears and sea otters are less adapted to aquatic living, spending most of their time out of the water.
While the number of marine mammals is small compared to those found on land, their roles in various ecosystems are large, especially concerning the maintenance of marine ecosystems, through processes including the regulation of prey populations. It is estimated about 23% of marine mammal species are currently threatened. Conservation for many of these species is complicated by their migratory nature, often crossing national boundaries and the fact that much of the earth's ocean realm is remote and lies beyond areas of national jurisdiction. Additionally the dynamic and often difficult conditions for people working in the marine environment adds to the cost and complexity of marine conservation in general.
To date SOS has funded both marine and aquatic cetacean projects and sirenian projects as well as one seal project.