18. Lower Bight of the Californias/Islas Coronados

Site Overview

This transboundary area is found just south of the Channel Islands and is situated just north of the coastal city of Ensenada (Mexico). The Lower Bight of the Californias incorporates coastal lagoons and submarine canyons, as well as the steep volcanic rock, which composes Islas Coronado and Islas Todos Santos.

This area is found inshore of the California Current and is a mixture of diverse oceanographic features. Estuarine circulation in the area results from the rivers in the region, such as the San Antonio and Tijuana rivers. Vertical mixing, significant upwelling and transboundary eddies lead to the elevated productivity of the area. These features aid in supporting many binationally significant fisheries, and the convergence of currents results in larval retention that produces locally high endemism.

The coastal strand is covered by native dune perennial species such as Abronia maritima, sometimes associated with wetland and coastal succulent scrub species. It is the southern limit of Atriplex leucophyla, a herbaceous Californian strand species (Moreno-Casasola et al. 1998, Espejel et al. 2001). Endangered wetland plant species occur such as Cordylanthus maritimus (Zedler 1982) and Triglochin concinna, which are on the Mexican endangered species list (Semarnat 2000). The Lower Bight contains kelp forests that support a diversity of marine life, including commercially valuable abalone and sea urchins. Aquaculture, such as that for bluefin tuna (Thunnus thynnus), is also an emerging industry in the region. Coastal pelagic fisheries, including sardine and chub mackerel, are vital to this area of Mexico. Several fisheries have suffered major declines, including large pelagic fishes such as swordfish, tuna and marlin. A resident population of green sea turtles also makes the bays—including San Diego Bay—and lagoons home, relying on algae and seagrasses for food.

The Islas Coronados are internationally significant for the breeding of many seabirds, including the ashy storm petrel (Oceanodroma homochroa), listed as near threatened by IUCN, brown pelican (Pelecanus occidentalis) and Brandt’s cormorant (Phalacrocorax penicillatus), as well as the approximately 750 breeding pairs of Xantus’ murrelets found on Islas Coronados (BirdLife International 2000), one of their key breeding habitats. A wintering population of Xantus’ murrelets is known to reside along the southern California Bight as well. The area is part of the Pacific Flyway.

Migratory marine mammals, including gray whales, converge on the area in the winter for breeding and calving following summer feeding in the waters off Alaska (Reeves et al. 2002). The islands are especially important haulout regions for the California sea lion, Pacific harbor seal (Phoca vitulina) and northern elephant seal.