Sunlight on the Sea of Cortez

Abstract

Sunlight on the Sea of Cortez George Keithley (bio) Seeking Warm Water The annual migration of Pacific grey whales begins in the fall, when they leave their feeding-bed in the Bering Sea as the ice floes thicken. Navigating the strait between Siberia and Alaska in the cold blue furrows among the Aleutian islands, small groups of pregnant females lead the way—their progress toward warmer water for birthing is the most urgent. Each of these pilot groups is followed by a dozen males and females, feeding and courting, while their young trail behind them, straying but hurrying to keep up. Similar to the adults, the youngest whales descend to depths of one hundred to three hundred feet as they swim southward to the subtropical coast of Mexico. Many of the expectant mothers will deliver their calves in the warm lagoons on the western brim of Baja California. Birthing and breeding occur in these waters from late winter into the first weeks of spring. For several hundred thousand years Pacific grey whales have made this migration, navigating by the distinct shape and feel of the ocean floor beneath their route; by the arc of the sun; by the coastal currents that envelop them; and by rarely halting to feed but extracting plankton from tons of seawater as they move along. And each year they communicate this learning to their offspring. Jaws, Lungs, Heart The mature grey whale is forty to forty-five feet in length. It feeds on huge quantities of miniscule life-forms. Other than plankton, its diet is mainly krill, shrimp-like creatures that attach themselves to the ocean floor. A toothless bottom-feeder, the grey whale has a shovel-shaped [End Page 440] lower jaw with which it scoops its food from the seabed. Each whale takes in huge mouthfuls. Then, using its tongue, it pushes silty water out through more than one hundred thin plates of baleen—whalebone that hangs from its upper jaw to form a filtering grille, or sieve—trapping plankton or krill but expelling the rest. As the whale dives, its powerful lungs contract. And while it swims and feeds beneath the sea’s currents, the grey’s heart rate drops drastically; the grey then uses the oxygen stored in its muscles and blood to remain underwater. When, eventually, it surfaces the pent-up oxygen is thrust out of a pair of blowholes on the top of its head in a forceful exhalation—that bright pale spume that we see rising above the waves. After Long Courtship In January and February many grey whales breed or give birth in the lagoons or near the islands off the west coast of the Baja Peninsula—San Martin, San Benito, Cedros—or in pristine blue water in the San Ignacio Lagoon, a haven the size of San Francisco Bay. One such island, San Martin, is actually a cluster of volcanic rock covered with lichens. Guadalupe fur seals seek the sun on these rocks. Here the sea is always moving, erupting from blowholes, streaming through tunnels, flowing out of the mouths of caves. And everywhere it has deposited shells of tender or delicate colors and gracefully ribbed arcs. There are large abalone shells, California Venus, Western calico scallop, and cowry. In the protected water, after long deep-sea courtships the urgent mating of the whales is an energetic embrace, seeking and clasping. Their moment of climax occurs; their clutching is sustained. Then tension and stillness, and the pair slip apart. As the young develop, they begin to feed on small crabs gathered from the ocean floor or from the floor of the coastal lagoon—scooping, sifting, consuming, and spewing out, as they are taught. From this point on a few pregnant females—“maverick moms,” the locals in Cabo San Lucas call them—will continue southward beyond the tip of the peninsula. [End Page 441] Rounding Cabo and coming almost to a halt, they will give birth in sheltered waters warmed by abundant sunlight on the Sea of Cortez: a downpouring light that appears to rise from the clear water into the air. The Pacific grey whales are annual visitors, but huge humpback whales are native to...