The Sea of Cortez or the Gulf of California is the 700-mile-long body of water embraced by mainland Mexico and Baja California. Its legendary productivity allows Mexico to catch 70% of its commercial fish here. How can a sea that no longer has a major freshwater input of nutrients from the Colorado River be so nutrient-rich? The answer lies within its unique oceanography.
The Pacific Plate once moved northwest off Mexico’s west coast and the Sea of Cortez did not exist. Over several million years the plate movement slowly rotated counterclockwise and produced incredible stresses upon western Mexico. This eventually moved the fault line eastward and slowly ripped off Baja California. The peninsula lifted along the west side of the newly forming gulf. There is a dramatic view of this escarpment of mountains above the town of Loreto. Farther north we know this fault as the San Andreas. In the south the ocean filled the growing basin to create the youngest gulf in the world. It now has a remarkable depth of over 2 miles at its mouth. Much of its width is over 80 miles across. This basin holds an incredible amount of water. Tides from the rise and fall of the Pacific Ocean pour in and rush out in a massive movement. The water mixes to a depth 1500 feet and causes a continuous clockwise current of 0.67 mph around the gulf in winter and a counterclockwise current in summer. The northern end has a 32-foot tidal range, the third largest in North America. Wind-induced currents also cause major movements of water during the winter. The wind drives the water at 3% of the wind speed and transfers as much as 40% of its energy.
When water moves away from an island or coastline it is replaced by water from below in a process called upwelling. All this water moving around in the gulf brings up not only deeper water, but large amounts of nutrients as well. All you need is an energy source of plentiful sunlight and “voila”, productivity, enough to grow a crop of phytoplankton that might turn the water red. The Sea of Cortez has been called the Vermilion Sea. The soup of phytoplankton feeds invertebrates that are gobbled up by more than 800 kinds of vertebrates including fish, blue and fin whales. The fish are consumed by people, birds, dolphins, porpoises, sea lions, sperm whales, humpbacks, and Bryde’s whales to mention just a few. There are also over 550 fin whales that are residents in the Sea of Cortez all year. It’s also one of the best places in the world to see blue whales in February and March.
The islands within the gulf have their own stories. Native people were active here and traveled by rafts made of aquatic bulrushes called tules. Archaeological sites are common on a number of the islands. Stone flakes, piles of discarded shells and signs of habitation provide evidence of early people found here long before European contact. Few islands have a reliable source of water, however, so they haven’t felt the heavy hand of modern man. Biologists working on how plants and animals become established where they are find the perfect laboratory within these islands. There is enough variation in island histories, ages, locations and topography to test and form theories about island biogeography.
Some interesting Sea of Cortez facts to explore are that the islands in this area are home to numerous species of unique plants and animals, and the number of species and abundance of marine mammals in this region of Mexico is unrivaled. These are some of the reasons why people who love whales, dolphins, seabirds and desert environments take vacations by land or small cruise ship to visit this unpopulated and exciting sea next to the Baja California Peninsula in Mexico.