The Gulf of California (Spanish: Golfo de California), also called the Sea of Cortés (Mar de Cortés) or Sea of Cortez, and sometimes the Vermilion Sea (Mar Bermejo), is a sea that is part of the Pacific Ocean. It separates the Baja California peninsula from the Mexican mainland. The gulf is bordered by the states of Baja California, Baja California Sur, Sonora, and Sinaloa, with a coastline of about 4,000 km (2,500 mi). Rivers that flow into the Gulf of California include the Colorado, Fuerte, Mayo, Sinaloa, Sonora, and the Yaqui. The surface of the gulf covers about 160,000 km (62,000 sq mi). The gulf has maximum depths over 3,000 meters (9,800 feet) due to its complex geology, which is connected to the movement of Earth's plates.
The gulf is believed to be one of the most diverse seas on Earth and is home to more than 5,000 species of tiny animals without backbones. Parts of the Gulf of California are a UNESCO World Heritage Site.
Geography
The International Hydrographic Organization says the southern edge of the Gulf of California is a line connecting Piaxtla Point (latitude 23°38'N) on the west coast of Mexico and the southernmost point of Lower California.
The Gulf of California is 1,126 kilometers (700 miles) long and 48 to 241 kilometers (30 to 150 miles) wide. It covers an area of 177,000 square kilometers (68,000 square miles), has an average depth of 818.08 meters (2,684 feet), and holds a volume of 145,000 cubic kilometers (35,000 cubic miles).
The Gulf of California is divided into three faunal regions: Northern, Central, and Southern. A recognized transition zone is the Southwestern Baja California peninsula. Transition zones exist between faunal regions, and they often differ for each species. Faunal regions are identified by the types of animals living there.
The Gulf of California contains 37 major islands. The two largest are Isla Ángel de la Guarda and Isla Tiburón. Most islands are on the west side of the gulf. Many of these islands formed from volcanic activity during the early history of Baja California. Examples include Islas Marías, Islas San Francisco, and Isla Partida. Each island formed from separate geological events. Some islands, like Isla Coronados, have volcanoes. The Colorado River Delta also includes islands such as Isla Montague.
The Gulf of California has more than 900 islets and islands, covering about 420 hectares. These were designated as a protected area for migratory birds and wildlife on August 2, 1978. In June 2000, the islands were also named a flora and fauna protection area. The Mexican government added these islands to the international "Man and Biosphere" (MAB) program and UNESCO’s World Reserve Network as a Special Biosphere Reserve. Conservation efforts are managed by four regional directorates, one for each state bordering the Gulf of California. A management program published in 2000 guides conservation work, supported by local plans. The Directorate of Protection Area Wildlife California Gulf Islands in Baja California oversees 56 islands near the state’s coast. These are grouped into four archipelagos: San Luis Gonzaga or Enchanted, Guardian Angel, Bahía de los Ángeles, and San Lorenzo.
The three general types of shores in the Gulf of California are rocky shore, sandy beach, and tidal flat.
The Gulf’s rich biodiversity and high number of species found only there are partly due to the types of rocks along its shores. Beaches with softer, more porous rocks (such as coquina limestone, rhyolite, granite, or diorite) usually support more species than those with harder, smoother rocks (like basalt or diabase). Porous rocks have more cracks and crevices, providing homes for many animals. However, the rocks must be stable on the shore for habitats to remain stable. The color of rocks also affects life on the shore. Darker rocks absorb more heat than lighter ones, which can make them less suitable for some animals.
The northern part of the Gulf of California has tidal ranges of up to 5 meters (16 feet). Mixed semidiurnal tides are common throughout most of the Gulf.
Some estuaries in the Gulf are "negative," meaning more saltwater evaporates than freshwater flows in. These estuaries have higher salinity and temperatures than the rest of the Gulf. These areas may have once been "positive" estuaries, where freshwater mixed with saltwater to create brackish water. However, human activity, such as water use for cities and farming, has reduced the number of rivers flowing into the Gulf. The upper Colorado River Delta is an example of a former major estuary and wetland that is now a small, temporary estuary due to dams and water diversions. Remaining estuaries still support many species of fish, crustaceans, and shellfish that are commercially harvested.
Although the Gulf’s shores are generally protected from the strong wave action seen elsewhere in North America, storms called "chubasco" can cause significant damage to shorelines, even though they are short-lived.
History
The first records of the gulf come from the marine expeditions of Fortún Ximénez, Hernán Cortés, Juan Rodríguez Cabrillo, Francisco de Ulloa, Hernando de Alarcón, Captain Francisco de Lucenilla, and Sebastián Vizcaíno. Melchior Diaz, an explorer who worked with Cortés, reached the northern part of the gulf in 1540. Juan de Oñate traveled overland in 1605 along the Colorado River. In the 19th century, Duflot de Mofras of France and C.H. Gilbert of the United States Fish Commission visited the area.
Geology
Geologic evidence shows that the Gulf of California formed about 5.3 million years ago when tectonic forces split the Baja California peninsula from the North American tectonic plate. During this process, the East Pacific Rise extended along the middle of the Gulf across the ocean floor. This area is called the Gulf of California Rift Zone. The Gulf would have stretched farther north to Indio, California, but the large delta formed by the Colorado River prevents the sea from flooding the Mexicali and Imperial Valleys. Volcanic activity is common along the East Pacific Rise. One example is the island of Isla Tortuga, which shows ongoing volcanic processes. Additionally, hydrothermal vents, caused by the stretching of Earth’s crust linked to the Gulf’s formation, are found in Bahía de Concepción, Baja California Sur.
Oceanography
The depth of water affects its temperature. Shallow water is more directly influenced by the air temperature nearby, while deeper water is less affected by changes in air temperature. In the gulf, water temperatures usually range from 16 °C (61 °F) in winter to 24 °C (75 °F) in summer. However, temperatures can vary widely. Water near the coast is often warmer than water in the open ocean. For example, the waters around La Paz reach 30 °C (86 °F) in August, while nearby waters in Cabo San Lucas only reach 26 °C (79 °F).
Sometimes, the northern part of the gulf experiences very cold winters. Water temperatures there can drop below 8 °C (46 °F), which can cause many marine organisms to die. Organisms most affected by these cold temperatures include large algae and plankton.
The narrow sea has a rich ecosystem. It is home to many unique species, such as the critically endangered vaquita and several types of sea urchin. It also supports many migratory animals, including humpback whales, California gray whales, killer whales, manta rays, Humboldt squid, and leatherback sea turtles, as well as the world’s largest animal, the blue whale. Some populations, like those of fin whales and sperm whales, live in the area year-round and do not migrate. Near the Colorado River Delta, a small group of totoaba fish still lives. This region has a long history of sport fishing and commercial fishing. However, data about fish populations vary greatly, and the gulf’s ability to recover from overfishing is uncertain. Changes on land, such as reduced water flow from the Colorado River into the gulf, have harmed fisheries, especially in the northern region.
The gulf supports many marine mammals, many of which are rare or endangered. Its more than 900 islands are important nesting areas for thousands of seabirds. Its waters are also key places for many fish species to breed, feed, and care for their young. For many years, the gulf has been a major source of two important fish species in Mexico: sardines and anchovies. Water pollution is a problem in the gulf, but the more urgent issues are overfishing and bottom trawling, which damage eelgrass beds and shellfish.
Efforts by the Mexican government to create protected areas and nature reserves have been limited by a lack of resources to enforce rules and by disagreement among leaders about how to protect the gulf. This is true even though parts of the gulf are a UNESCO World Heritage Site. The gulf’s long coastline is difficult to monitor, and the powerful commercial fishing industry has been slow to support conservation efforts that could help the environment. Conservation efforts are also complicated by a history of too many fishing boats and the negative effects that conservation rules can have on people who live along the coast. Currently, the Mexican government and businesses are promoting large-scale tourism development in the gulf, but the effects of this on the environment and local communities are unclear. In 2019, the gulf was added to the List of World Heritage in Danger due to concerns about the possible extinction of the vaquita, a porpoise found only in the area.
Coastal communities depend heavily on both commercial and sport fishing. These communities include San Felipe, San Carlos, Cabo San Lucas, La Paz, Loreto, Guaymas, Bahía Kino, Puerto Peñasco, Topolobampo, and Mulegé. The well-developed shrimp and sardine fishing operations in Mazatlán, on the Pacific coast of Mexico, also heavily use the southern gulf’s resources.
Many marine organisms can only live in specific salinity ranges, which influences the types of fish and other creatures found in the gulf. The average yearly salinity in the Sea of Cortez ranges from 3.5% to 3.58% at the surface. Salinity in the northern part of the gulf is generally higher than in the central and southern areas because more water evaporates there.
Locals have reported the existence of a large creature called the "Black Demon" (Spanish: El Demonio Negro) in the Sea of Cortez. It is often described as a black shark, and less commonly as a whale. It is said to be about 20 to 60 feet (6.1 to 18.3 meters) long and weigh 50,000 to 100,000 pounds (23 to 45 tons), similar to the estimated size of the megalodon. This is one of several reported sightings of large sharks in the Pacific Ocean during the 20th and 21st centuries.