Rocks & Islands


Offshore rocks and islands provide critical habitats for marine species. In addition, California’s islands support numerous rare, endemic species that have survived – and evolved – as a consequence of that isolation.

The Farallon Islands, the most prominent islands in the sanctuary, provide important breeding and resting sites for many of the marine birds and mammals that migrate through the sanctuary. In addition, there are a number of coastal rocks and islets within the sanctuary, such as Bird Rock (near Tomales Point), Double Point and Point Resistance rocks (near Point Reyes) that are important breeding and resting sites.

The sanctuary manages the marine environment below the mean high tide line for all exposed rocks and islands within its boundaries. At the Farallon Islands, land above the mean high tide line constitutes the Farallon National Wildlife Refuge and is managed by the US Fish and Wildlife Service.

Islands and offshore rocks provide some safety from natural enemies, as the water around the islands is a barrier to predators and other pests. Birds and pinnipeds use islands for breeding, resting, molting and other activities; there, they remain safer from many of the threats they would face on a mainland shore, such as terrestrial predators and human disturbance.

In the 1800s and early 1900s, California’s offshore islands were targeted by hunters – for animal fur, meat, blubber and eggs. The use of boats and other maritime tools made the islands accessible; and the large numbers and generally docile behavior of the animals on islands made them easy, and profitable, prey. In fact, hunting resulted in the near extinction of northern elephant seals, Mirounga angustirostris, northern fur seals, Callorhinus ursinus, Common Murres, Uria aalge, Cassin’s Auklets, Ptychoramphus aleuticus, and Tufted Puffins, Fratercula cirrhata, from the California coast.

Today, the Farallon Islands, located 48 kilometers (30 miles) west of San Francisco, are protected by the Farallon National Wildlife Refuge, established in 1909. The Farallones consist of seven islands that are part of a granite ridge that rises along the seafloor at the western edge of the continental shelf and lie within one of the largest upwelling centers in the world.

Southeast Farallon and West End (a.k.a. Maintop) islands together cover about 0.35 square kilometers (about 87 acres). Southeast Farallon Island is the largest of the Farallones and has a history of human occupation. Middle Farallon Island is an exposed rock located about four kilometers to the northwest, and the North Farallon Islands are a group of four larger rocks located eight kilometers farther to the northwest. Southeast Farallon Island is largely exposed granite rock with some soil and sparse herbaceous cover of native annual plant communities.

Restoration programs have removed some of the invasive mammals on Southeast Farallon Island, although invasive mice and plant species are still causing destruction to nesting birds and their habitats. The other islands, lacking a history of human occupation, are not known to have invasive pest problems.

The other rocks and islets that make up the Islands and those found elsewhere in the sanctuary are exposed rock habitats, with typical assemblages of rocky shore species. The larger rocks and islands also have small sandy cove beaches.

Human Impacts
Offshore rocks and islands are critical habitat for many sanctuary birds and marine mammals, which gather on them in large numbers to breed, molt and rest. The congregation of animals in these areas has historically made them easy targets for human hunting and egg-gathering activities.

Although these activities are now prohibited, marine birds and mammals are still at risk from human activities, and the effect of these activities is magnified because so many animals are gathered in one place.

Potentially harmful activities and phenomena include:

  • Vessel traffic and lights
  • Low-flying aircraft
  • Oil spills
  • Overfishing
  • Global climate change (which affects habitats and food abundance)

Close vessel passes and low-flying aircraft are known to create behavioral changes in wildlife, including flushing (startle into flight), stampeding (a rush of frightened animals) and abandonment (of nest, eggs or young).

Historically, the total number of spills from transiting vessels is small, but the potential impacts are enormous, given the number and volume of vessels and the hazardous cargo lane’s proximity to the Farallon Islands and major seabird and marine mammal populations. As demonstrated by the 2007 Cosco Busan oil spill in San Francisco Bay, there is considerable risk of vessel spills from container ships that transit the gulf and the bay. The potential impacts are even greater for spills from oil tankers carrying Alaskan, Californian and international oil up and down the California coast.


The following list includes some of the projects underway in the sanctuary. Please click on the Projects tab at the top of this page for more information.

Monitoring at the Farallon Islands
The majority of monitoring studies at the Farallon Islands are coordinated efforts between PRBO Conservation Science, a non-profit organization, and the United States Fish and Wildlife Service. These organizations are involved in several projects, including studying seal and sea lion abundance and reproduction as well as examining reproduction, feeding ecology and population dynamics in seabird species that breed on the islands. Other researchers study shark behavior, abundance, feeding and distribution around the Farallones and near Point Reyes Headlands.

The sanctuary is also involved in monitoring efforts on the Farallon Islands. Staff collect intertidal monitoring data, for example. Through regular assessment of the condition and health of this sensitive habitat, we can detect acute changes and long-term trends. Monitoring information can also indicate if a particular management action is effective.

Seabird Protection Network
This effort, spearheaded by the Greater Farallones National Marine Sanctuary and in cooperation with the U.S. Fish and Wildlife Service Common Murre Restoration Project and other agencies, sanctuaries and non-governmental organizations, is a new program aimed at improving the survival and recruitment of central California coast seabird colonies harmed by the 1998 Command oil spill. The program addresses one of the biggest obstacles to the recovery of these populations: human disturbances. The goal is to reduce human disturbances at seabird breeding and roosting sites from Point Reyes to Point Sur, with an emphasis on species most affected by the Command oil spill.

Photo Library

No photos are currently available for this section.

Map Repository

No maps are currently available for this section.

Project Database

No projects are currently available for this section.