The Marine Mammal Protection Act formalized a program to provide response to reports of strandings of marine mammals and unusual mortality events. This was done by creating a network of parties from different locations that would be responsible for responding to stranding events within their zone.

Most stranding zones in California are defined by county boundaries. Some zones include only one or two counties, but California's largest zone covers 8 coastal counties and includes another 10 where the San Francisco Bay and Sacramento - San Joacin River Delta reach inland. Los Angeles county has its coastline divided into two stranding zones, and one of those two zones also has multiple (2) organizations responsible for strandings within it.

Stranding reporting areas of the coast of Oregon and Washington and Puget Sound are based upon theauthorizations for each facility in their Stranding Agreement (SA) - each SA lists a primary response area granted to the organization, and these lines correspond to that. These zones are often divided more by geographical considerations than by political boundaries, such as island groups or cross-water zones. One zone is the responsibility of two differeent organizations because each has a different specialty. The Cascade Researh Collective is responsiblt for Cetacean strandings in that area and Washington Department of Fish and Wildlife Marine Mammal Investigations is responsible for pinniped strandings in the same area.

A stranding is:

• a dead marine mammal on the beach or in the water;

• a marine mammal that is alive on the shore and unable to return to the water under its own power;

• a marine mammal that is alive on the shore and, although able to return to the water, is in need of apparent medical attention;

• a marine mammal in the water and cannot return to its natural habitat under its own power or without assistance.

In most stranding cases, the cause of the stranding is unknown, but some identified causes have included disease, parasite infestation, harmful algal blooms, injuries from ship strikes or fishery entanglements, pollution exposure, trauma, and starvation. While most stranded animals are found dead, some strand alive. In a limited number of cases it's possible to transport them to regional rehabilitation centers for care. In rare cases, successfully rehabilitated animals are returned to the wild.

With the passage of the Endangered Species Act, in 1973 and the Marine Turtle Conservation Act of 2004, protection of sea turtle species, most of which are endangered or threatened, has resulted in them being added to the list of species which stranding organizations are responsible for.