The Sea of Cortez The name alone evokes romance, call like a siren, promises glimpses of Shangri La. It is a magical place, there’s no doubting it. And it’s a biological wonder as well; one that has held the fascination of naturalists and adventurers since the Spanish sea captain Hernando Alarcón first sailed to the head of the Gulf in 1540.
Also known as the Gulf of California (both names are equally valid, and both derived from sixteenth century Spanish maps), this great sea is over 700 miles long and spans nine degrees of latitude, crossing the Tropic of Cancer near the city of La Paz. It was created around 6 million years ago, when tectonic forces ripped the Baja California Peninsula away from mainland Mexico, allowing the waters of the tropical Pacific to rush into the newly formed basin. The great East Pacific Spreading Center runs right through the middle of the Gulf, and continues to push Baja (and much of California) away from the North American Plate at a rate of several inches per year. The sea divides the Sonoran Desert into two halves, on the “mainland” and on the Baja Peninsula, with southern Arizona being the capstone connecting the two parts.
Its warm subtropical waters, and abundant upwellings that bring deep-sea nutrients and oxygen to the surface, have created one of the most productive and diverse seas on the planet. The Gulf’s 6000 recorded animal species are estimated to represent only about 70% of the actual (total) fauna lurking in its rich waters. So productive is this sea, that about half of Mexico’s total fisheries production comes from the region. So rich in plankton and other marine life is the Sea of Cortez, that populations of two species of migratory great whales appear to have forsaken their ancestral migratory instinct and taken up permanent residence there – sperm whale (Physeter macrocephalus) and fin whale (Balaenoptera physalus). Sperm whales are the largest of all the toothed whales (to 60 ft in length) and are among the deepest divers in the ocean, routinely reaching depths of 3000 ft or more; their major prey, the jumbo (or Humboldt) squid (Dosidicus gigas) can weigh more than one hundred pounds. Jumbo squid have become so abundant in the Sea of Cortez, that these days on a good night local fishermen may pull in 10,000 pounds or so, in one locality. However, abundances of this squid fluctuate dramatically from year to year for reasons we are only just beginning to understand. Seven marine reptiles inhabit the Sea of Cortez, five threatened/endangered sea turtles, one sea snake (Pelamis platurus), and one crocodile (Crocodylus acutus).
The direct influence of the Sea of Cortez even reaches Tucson, and much of the Southwest, in the form of summer monsoons. Once thought to originate in the Gulf of Mexico, we now know that almost all of the summer monsoon rain comes from the Gulf of California/Tropical Eastern Pacific, often in masses of water-laden air called “Gulf Surges” that rush right up the Sea of Cortez to dump their harvested moisture in southeastern Arizona and adjacent areas, making the Sonoran Desert a “maritime desert.” The oceanic waters of the Pacific also rush up the length of the Gulf, twice daily, and as they funnel into the shallow, narrow uppermost Gulf, they create some of the world’s largest tides—up to 24 vertical feet at Puerto Peñasco (“Rocky Point”) and over 30 feet at the very head of the Gulf. On shallow tidal flats in the northern Gulf, a 20-30 ft vertical fall can expose kilometers of twice-daily-submerged seabed, with the sea rushing back in just a few hours later. Many a naive tourist has watched the sea swallow their off-road vehicle with these rapidly returning tidal waters. On average, more than 25 X 109 m3 of tidal water flushes into and out of the Upper Gulf daily; more than the entire flow of the Colorado over an entire year! With over 900 islands and islets, the Sea of Cortez is home to one of the world’s largest island archipelagos.