UNLIKE THE EMERGING THREAT of new diseases and the resistance to antibiotics, one doesn’t have to wait to see how man’s interference is changing the marine environment. Many of those changes are already here. One shining example is the Gulf of California between mainland Mexico and the Baja California peninsula, what was once lovingly referred to as the “Baja Fish Trap” for its abundance of marine life. Overfishing, acidification, and warming waters have altered the ecology of these famous marine waters. The marlin, swordfish, and sharks that anglers once came here for have dramatically dwindled and a new ecology made up of Humboldt squid and sperm whales has taken over.
It is still a pristine environment. A drive south of the US border down Mexico’s Highway 1 takes you past volcanoes, mountains, and sculpted red rock through a series of valleys populated with whiplike boojum trees and giant cardon cacti. About five hundred miles south of the border it summits the coastal mountains and descends rapidly onto the Gulf of California just above the historic French mining town of Santa Rosalía. The Gulf of California, in Mexico, was created six to ten million years ago when Baja California began to separate from mainland Mexico, producing the geologically diverse peninsula and the biologically diverse waters of the Gulf.
On a recent visit, the moist evening breeze brought in the briny smell of marine life to cool the town of Santa Rosalía as the fishermen headed toward the dock and the boats for the nighttime catch. Biologist William Gilly, from Stanford University’s Hopkins Marine Station—a big, friendly academic with lots of interesting stories—and his group of student researchers joined the fishermen as they motored out to sea. It was September on the Baja Peninsula, where open-ocean schools of tuna, swordfish, and sharks were once an annual gift of the Gulf, but have diminished in recent years.
Now Santa Rosalía fishermen pursue Humboldt squid (also known as jumbo squid), which appear to have replaced many of the finfish in the Gulf of California. They still fish as before, only they go out in the late evening, not at dawn. At sunset, I watched the local fishermen join the parade of pangas, twenty-two-foot open skiffs with outboard motors that departed from the sandy shores. The Gulf waters turned from blue to black as the boats lined up about a mile offshore, their colored lights glistening in the evening shadows. The fishermen used hand lines baited with fluorescent jigs to catch the squid.
These boats represent a growing group of local small-scale fishermen who, but for their outboard motors, rely little on the hardware of the modern commercial fishing industry. Instead, they fish the waters off the Baja Peninsula from unregulated camps that line the shore using primitive gear. Over the last decade the Mexican Humboldt squid fishery has caught between 50,000 and 200,000 tons of squid annually, mostly from the Gulf of California, and sold it predominantly to markets in Korea and China.
The Humboldt squid was named for the Humboldt Current, an ocean current that flows north along the west coast of South America from the southern tip of Chile to northern Peru. It was thought that the Humboldt squid in Baja originated in Pacific waters off South America, though when, exactly, they arrived off Baja is a mystery. There have been few historical sightings of the squid in marine records farther north than the Galápagos Islands off South America.
Humboldt squid (Docidicus gigas) have not only invaded the waters of the Gulf of California, they have expanded their domain northward along the Pacific coast as far as Alaska and westward along the equator toward the Hawaiian Islands.
Squid here seem to have filled a niche left vacant when finfish such as tuna, sharks, marlin, and swordfish began to disappear in the late twentieth century. Squid have a much shorter life span than other fish, rarely living over a year and a half. And they are highly productive, meaning they can bounce back from fishing pressure much faster than finfish, which are not as productive. But Gilly thought this factor was less important than the ability of squid to cope with the spread of low-oxygen waters, a new problem on the horizon that may be giving the squid their ticket to expand.
The increase in the biomass of Humboldt squid in the Gulf of California is promoted by the development of low-oxygen zones in the water, a result of climate change and possibly decreased ocean circulation. These zones are different from the dead zones created by agricultural runoff, but the two could act in tandem to worsen the effects. Low-oxygen waters support fewer species but can support high quantities of those few species that are tolerant of it. Again, we are seeing the live-fast-die-young generation: a few species that are able to survive a toxic environment, which then take over the world—or the ocean in this case.
Santa Rosalía developed as a copper mining town in the late 1800s, and it was prosperous until the ore ran out in the 1920s. Still there are touches of prosperity from its mining days. Gustave Eiffel, of Eiffel Tower fame, built the church in the town center in France and then shipped it to this Baja town, where it was reassembled in 1897, an indication of the wealth mining generates. Still the town has none of the lights, bars, or tourist trappings you might find in Puerto Vallarta or Acapulco farther south.
The Santa Rosalía copper mine has recently reemerged as newer techniques have made the mining of old ore deposits viable. Gilly wonders what the long-term effects will be as the mine gears up for another run. Only, the proportions are much larger now than in the late 1900s, as miners will be using huge equipment to extract lower amounts of copper from already-mined soils.
Gilly has developed a program for monitoring intertidal shellfish communities, both near the new mine and in a more protected area about twenty miles north of town. “If the mine begins to disturb the marine environment off Santa Rosalía, the monitoring plan is designed to detect it. We’re lucky to be able to commence monitoring before major production commences,” said Gilly. He’s working with students from a local technology school that was established here in recent years.
Still his biggest concern is the changing face of oxygen in the deep ocean, here and in the oceans around the world. Gilly referred me to a paper by Lothar Stramma, a physical oceanographer at Kiel University in Germany, who led a study in 2008 that analyzed oxygen content at six different spots in the deep waters of the Pacific, Atlantic, and Indian Oceans. That study found significant increase in low-oxygen water in most spots, and these areas, known as oxygen minimum zones, were below the livable threshold of many marine animals. These low-oxygen zones are a natural phenomenon of the eastern Pacific Ocean and occur in the upper layers of the water, but they are expanding in all directions worldwide. Scientists link this change to global warming.
The oxygen minimum zone restricts the depth to which tropical open-ocean fishes, such as marlin, sailfish, and tuna, can go by compressing their habitat into a narrow surface layer, where they are more easily fished out. In general, the Pacific has lower oxygen minimum zones than the Atlantic. German oceanographer Stramma said that the lowest oxygen value in the Atlantic found in the 2008 study was 40 percent saturation (surface is 100 percent), whereas in the Pacific there were oxygen minimum zones that reached almost zero percent.
This has serious consequences for marine organisms. According to Gilly, at 10 percent dissolved oxygen content in the water, microorganisms can no longer utilize oxygen and start metabolizing nitrogen compounds, releasing nitrates, which are strong greenhouse gases. “At zero percent, microorganisms start metabolizing sulfate ion compounds and releasing hydrogen sulfide, and that can be lethal,” said Gilly. During the Permian extinction the oceans went stagnant in places, caused by a loss of ocean currents. Douglas Erwin at the Smithsonian thinks that the emergence of this chemical compound into the atmosphere may have been one of the dominant killing forces at the time.
Humboldt squid feed on lantern fish in the Gulf of California but may prefer hake in Chile and Peru as well as off Northern California. “Hake” is a term that includes any of several large marine fishes of the cod family. South American authorities struggle with problems in their hake fishery, which is squeezed between overfishing and oxygen-starved waters. Northern California’s hake fishery has not been affected by oxygen-starved waters, though bottom-dwelling creatures have.
Off the Oregon and California coasts, the oxygen minimum layer is rising up and moving nearer the shore. “It’s intersecting the continental shelf and moving rapidly inland like a river breaching its levees,” said Gilly. “And there are a lot of things that live at the bottom that can’t swim away.”
The presence of large numbers of Humboldt squid off the Pacific Northwest has impacted the valuable hake fishery there. For example, in 2009 there were so many squid present in the areas of hake schools that sonar estimates taken of hake numbers could not be used to set national quotas for the US and Canadian hake fisheries.
Few predators catch squid at these depths. Gilled finfish like tuna and shark can dive to the upper limits of the oxygen minimum zone and feed on squid there, but few can go into the zone and stay there for a significant length of time. Scientists at Stanford University have tracked great white sharks, which migrate annually toward Hawaii, and have found that large numbers of these animals stop en route at a mid-ocean area called the “White Shark Café,” where they repeatedly engage in dives above the oxygen minimum zones. Whether they are mating or feeding is not yet known, but Gilly thinks they could be diving for Humboldt squid or the purple-back flying squid that may also inhabit the area.
Fertilizer runoff from the mainland shores in the northeastern part of the Gulf may be enhancing the low oxygen effects here. Such runoff has created dead zones at the mouth of the Mississippi River in the US; the mouth of the Yangtze River in China; within the Black Sea Basin in eastern Europe; in the Skagerrak, the strait that separates Norway and Sweden from Denmark; and in the Cariaco Basin, near the coast of Venezuela. There are more than 150 such dead zones around the world.
The difference between dead zones and low-oxygen zones is that the latter involve an oxygen deficiency in the specific layer of water that forms beneath the maximum depth of daytime surface light in coastal and mid-ocean environments. Scientists measuring that layer of water, between 650 and 3,000 feet (200 and 700 meters), have found a measurable decrease in oxygen and an expansion of the vertical and horizontal limits of the layer over the last fifty years.
This maximum depth of daylight surface light is also known as the deep-scattering layer, a name given to it by twentieth-century naval captains who found that sonar gave a false seafloor echo as it bounced off this zone because of the high density of marine life present. Plankton and zooplankton congregate in the deep-scattering layer primarily to avoid visual predators, and their feeding habits use up dissolved oxygen in the water, creating the oxygen minimum zones.
Few marine creatures have adapted to the oxygen minimum zones. But Humboldt squid are one of these low-oxygen-tolerant wonders. When they enter the zone, their metabolism slows and they consume less than 20 percent of the oxygen they need at the surface. Specialized gills allow them to scavenge oxygen from the water more efficiently. Their hearts don’t race wildly as they chase down their prey, since their prey are slowed down by the lack of oxygen as much as the squid are. “It’s not like a lion chasing after a gazelle,” says Gilly. “They catch fish with little effort.”
What are known as “common market squid,” a smaller but important part of the California fishery, probably find such zones lethal. Gilly, who has studied both common market squid and Humboldt squid for decades, believes that increasing loss of oxygen in the seas will lead to the expansion of Humboldt squid from this point forward. This is bad for finfish, as the larger fish—already crowded into shallower oxygen-rich zones—will become more vulnerable to commercial fishing. Such a situation is happening now off the coast of Peru and Chile around the Humboldt Current, one of the richest fisheries on earth, where catches are high but the sustainability of these catch rates is in doubt.
Climate change is the chief suspect in this developing tragedy. Warmer ocean waters hold less oxygen, and a warmer climate generates less wind to oxygenate surface waters. The result is a more stratified ocean with a surface layer of warm water riding on cooler, denser water, which impedes the mixing of oxygen. In addition, shrinking ice at the poles may be slowing deep-ocean circulation, which brings oxygenated waters to the deep waters of the Pacific and Atlantic Oceans.
During that Permian extinction 250 million years ago, increased atmospheric CO2 warmed the planet, which stripped the ocean of its oxygen and wiped out more than 90 percent of the creatures in the sea. Oxygen deprivation was a major source of extinction during the Cretaceous extinction as well.
Bigeye tuna, swordfish, and sharks can dive to the top of the oxygen minimum zone, but few finfish can go into it for any length of time. Sperm whales, elephant seals, and some sea turtles are among the best penetrators of this zone, but it takes serious adaptations to withstand the pressure and the lack of oxygen. For the few that can, the upper boundary of the oxygen minimum zone is a hidden treasure where life abounds.
To show the extent of change that has occurred over the last half century, Gilly likes to refer to descriptions by the author John Steinbeck and the marine biologist Ed Ricketts, who in 1940 took a trip around the Baja Peninsula into the Gulf of California surveying the marine life. Steinbeck wrote a book about the journey, called The Log from the Sea of Cortez—the Sea of Cortez being the more traditional, more romantic name for the Gulf—describing his trip with Ricketts and a crew of fishermen from Monterey, California. Steinbeck had featured Ricketts, who made a living at his lab on Cannery Row by preserving specimens of marine life and selling them to schools for use in biology laboratories, in two of his novels, Cannery Row and Sweet Thursday.
The purpose of the Steinbeck/Ricketts expedition in 1940 was to collect samples in the tide pools along the shores of the Gulf of California over a six-week tour. The group left Cannery Row in Monterey at a time when Hitler was invading Denmark and moving up toward Norway and “there was no telling when the invasion of England might begin,” wrote Steinbeck. But they put the world’s drama in their rearview mirror, and boarded the Western Flyer, a chartered sardine boat, heading for Baja California, Mexico.
Three days later, they eyed the lighthouse at Cabo San Lucas, at the southern tip of the peninsula, and at about 10 p.m. they rounded the cape and entered the dark harbor. Except for the lighthouse, there were no lights in the harbor. Today, Cabo San Lucas is a full-blown mega-resort, with lights that stay on all night. Then it was a sleepy little village where it took Steinbeck and Ricketts all day to find the authorities in order to get their visas stamped.
The first Mexican town Steinbeck described at length in The Log from the Sea of Cortez was La Paz, a large port around the southern tip of Baja coming from the Pacific. I visited La Paz last summer and witnessed the various efforts being made to compensate local fishermen for the reduced catches they and their hungry families are encountering.
Frank Hurd is the science director of Olazul, a group of American and Mexican scientists and innovators working with local fishing communities to develop sustainable systems of aquaculture as an alternative to depleting overfished stocks. Hurd invited me to see his version of an offshore, semimobile aquaculture pen. One morning before dawn we drove out from the city to a fish camp on the northern shores of La Paz where Hurd and his associates had been testing a spherical pen, 277 cubic yards (212 cubic meters) in volume, about three miles offshore. Hurd said Gulf currents could flush out the wastes and bring in nutrients and oxygen for the shrimp he was testing. The structure was made from recycled and reinforced polyethylene timbers wrapped in coated steel mesh netting “built to withstand the occasional hurricane that rolls up the Mexican shoreline during the summer and early fall,” said Hurd.
In his book, Steinbeck had described on their Sea of Cortez journey how they trolled a couple of lines off the back of their boat and were pretty much able to keep themselves in finfish such as yellowfin tuna, skipjack, Mexican sierra, red snapper, and barracuda the whole trip. Hurd said that the local fishermen in La Paz described similar catches in the old days but today try to make a living selling trigger fish, sand bass, bonito, mackerel, and other species that were considered trash fish back in Steinbeck’s time.
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The Sea of Cortez that Steinbeck investigated over seventy years ago is not the same body of water that Gilly and his crew motored to in 2004. In his log, Steinbeck described marlin and swordfish frequently leaping out of the ocean into the air and dancing across the surface of the water. The scientist described seeing only a couple of small squid on his entire six-week excursion in the Gulf of California. And there was nothing that resembled a Humboldt squid.
Gilly also spent some time looking through historical records for sightings of Humboldt squid. There were isolated reports in the scientific literature going back to 1938, but no reports of large numbers until commercial fishing for them commenced in the late 1970s. He queried a number of old fishermen in the Gulf, and none of them remembered sighting the squid before that. Humboldt squid were absent in the natural history of the Gulf written by early Jesuit missionaries. James Colnett, an officer of the British Royal Navy, saw no Humboldt squid in the area south of Cabo San Lucas in 1793–94, though he described squid “of four or five feet in length” at the surface off the Galápagos Islands. “But that’s a far way off,” said Gilly. The squid must have migrated to the Gulf of California since Colnett’s time, but details of the move are lacking.
Humboldt squid appear to have evolved in the southeastern Pacific where El Niño events warm the surface waters of the ocean every four to twelve years, creating unusual global weather patterns. Changes in the Humboldt squid fishery mirror changes in El Niño–driven weather. Though Gilly and his associates measured high concentrations of squid in the central Gulf in 2012, they had moved away from the shore and their sizes had decreased. Gilly thought an earlier El Niño event in 2009–2010 led to the animals’ accelerated sexual maturity, what he called an even more radical live-fast-die-young life strategy in the face of an uncertain future.
Humboldt squid have two tentacles that can reach out and grab prey and eight arms to envelope them. The squid can attain eight feet in total length (mantle plus tentacles). They use their tentacles and arms to subdue prey and their razor-sharp parrotlike beaks to tear them apart. They are some of the fiercest of the cephalopods, a group of animals that includes squid, cuttlefish, and octopus.
Humboldt squid are also famously cannibalistic. Unai Markaida, a marine biologist at El Colegio de la Frontera Sur in Campeche, Mexico, studied prey items of 533 Humboldt squid and found evidence of other Humboldt squid in 26 percent of their stomachs. Fishermen who pursue the Humboldt squid tell scientists that once squid are hooked, other squid start attacking and eating the fishermen’s catch. The fishermen have to pull their catches in fast to avoid these voracious attacks.
The Humboldt squid is particularly fast and propels itself through the ocean as if by jet engine. It draws water into its mantle and then ejects it through a spout like a rocket. All squid have the ability to change color quickly, some imitating patterns, even textures of sandy bottoms or rocky reefs. Humboldt squid lack this patterning capacity but are able to switch back and forth from maroon to ivory, pulsing like a strobe. The capability to communicate through color change is quite profound for a creature that is related to the snail. According to Gilly, “There’s jitter [vibration], variation, and change in the frequency between two squid. It’s highly unlikely this isn’t some kind of communication.”
Up to four million Humboldt squid hang out in the Sea of Cortez near Santa Rosalía at about one thousand feet (three hundred meters) during daylight near the shelf where the bottom starts falling off sharply, but move up at night when the deep-scattering layer moves up as well. It’s then that the fishermen initiate their attack. Hauling up a squid that can weigh up to a hundred pounds by hand lines is a rough job at night, particularly when the average price for cleaned squid is less than ten cents a pound (0.5 kilos).
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One winter day, I caught up with Bill Gilly at the Hopkins Marine Lab on Cannery Row, next to the Monterey Bay Aquarium. People claim there are differences but also a lot of similarities between Gilly and Ed Ricketts, who accompanied Steinbeck on his journey to the Sea of Cortez.
Ricketts’s lab on Cannery Row was a hangout for authors, illustrious locals, and street people. Gilly’s lab is more of a gathering place for assorted Stanford students. Ricketts, according to Steinbeck, lived across from the local house of prostitution but never visited the house after dark unless he’d run out of beer and the stores were closed. Gilly lives next to the Monterey Bay Aquarium and goes there frequently. In Steinbeck’s eulogy he said Ricketts “loved to drink just about anything.” Gilly would admit only to enjoying the occasional beer. Their greatest similarities are that Gilly, like Ricketts, is a biologist who loves Monterey, Baja, and the Gulf of California and likes to laugh.
When Gilly announced his plan to retrace Steinbeck and Ricketts’s 1940 voyage through the waters and intertidal zones of the Gulf of California, he received a surprising call of support when the owner of North Coast Brewing Company called and offered his services. “You know those guys drank a lot of beer on that trip,” he said. “And I’m the man that can help you with that.” Gilly reacted with a smile.
Gilly and his team arrived at the boat on their date of departure and found two shrink-wrapped pallets of beer with a sign on it that said FOR DOCTOR GILLY. Inside the shrink-wrap were seventy-two cases. “It was the most beer I’ve ever seen outside of a Princeton reunion I once attended,” laughed Gilly when he told me the tale.
In the end, Gilly and his crew drank only about 1,242 beers. Steinbeck and his crew drank 2,160 beers. “And they did that with a smaller crew and a shorter trip,” said Gilly in awe.
There were other differences in the two expeditions that were not as lighthearted. At the various intertidal zones that Steinbeck and Ricketts visited, the author repeatedly used expressions like spiny-skinned starfish in “great numbers,” and “knots” of brittle stars, but Gilly’s team did not observe a great number of either at any of the tide pools they witnessed.
Steinbeck and Ricketts encountered “huge” conches and whelks (large sea snails and their shells) at several sites and a great number of large Turbo snails (shaped like a turbine). Gilly’s crew found only small living specimens of conches and Turbo at just a few sites, and dead whelk shells at one. In 1936, William Beebe, an American naturalist, explorer, and marine biologist, found a beach just north of Bahía Concepción—about midway up the eastern shore of the Baja—that was what he called “a conchologist’s paradise,” with shells “of amazing size and a host of species.” Tellingly, Gilly’s crew found a dramatic decline in all these species.
One of the greatest and most disturbing changes in the Gulf is in the “pelagic,” or open-ocean, predatory finfish that inhabit the upper portion of the water column and aren’t associated with the shore or the bottom. Although Gilly and company traveled at the same time of year, using the same type of boat, and for about the same duration as the Steinbeck adventure, they witnessed a greatly changed community of open-ocean fish.
Steinbeck and Ricketts wrote, “We could see the splashing of great schools of tuna in the distance, where they beat the water to spray.” The pair also saw marlin, sailfish, and swordfish, but Gilly’s team sighted few of these.
Gilly’s team did catch sierra mackerel and yellowtail, but neither fish was of the same size or in the same numbers as Steinbeck and Ricketts had reported.
Steinbeck and Ricketts got a look into the future, though they didn’t realize it at the time, when they boarded a shrimp trawler off Guaymas on the mainland side of the Gulf and witnessed the unintended consequences of the fish species that came up with each net. Though the fishermen tried to separate the shrimp from the rest of the catch and tossed back the unwanted fish, most of these died belly-up in the water. Today shrimp trawling is recognized as the single most ecologically damaging activity in the Gulf.
Sharks, particularly the enormous schools of hammerheads that once circled the sunken islands, or seamounts, in the middle of the Gulf, have declined in size and number. The same is true with manta rays: they have been replaced with smaller mobula rays than the ones seen by Steinbeck and Ricketts. Steinbeck wrote of the attempted landing of a number of huge manta rays, but the rays always broke the line, even when it was three inches thick. And Steinbeck and Ricketts noted several other species of squid but not Humboldt.
Though Gilly never saw the abundance of marine life that Steinbeck had witnessed, he found his own vision when he got to San Pedro Mártir Island, an area known for hosting many sperm whales. Since sperm whales eat Humboldt squid, Gilly figured there must be a lot of squid, and this was the reason for taking this detour, which had not been a part of Steinbeck’s journey. He was looking for baby Humboldt squid, something nobody had ever found in the Gulf. Satellite data had told him there was an intense tidal upwelling event (tides bringing the rich waters of the deep up toward the sea surface), and he guessed that the forward edge of this rich marine zone might harbor tiny squid larvae. On his second net tow, he found two baby squid a quarter of an inch long. But there was more.
It was a place where “all the life was, plankton, fish, squid, and whales,” reported Gilly. The biologist and his team were greeted by a nonstop squid review, with Humboldt squid darting in toward the boat and flashing their underbellies in attempts to lure small schooling fish near the surface. The show continued until after midnight.
They didn’t set anchor, since the sea was more than 3,300 feet (1,000 meters) deep, so they simply drifted all night. At one point, large sperm whales were lounging at the surface with fins exposed, some in pairs, showing their flukes before diving. Gilly had never seen a sperm whale before, yet he knew they were hanging out because Humboldt squid, their favorite food, were there in abundance.
Said Gilly, “We had come to the Sea of Cortez to discover how things might have changed since 1940—and here on the open water was the most dramatic ecological change witnessed during the entire trip, the apparent arrival of two major predators far offshore from the rocky reefs that were scoured by Ricketts and Steinbeck. This was a profound and qualitative change—an ecological regime shift.”
It was the apex of a new evolution, one made up of squid and sperm whales, which had replaced the vision of tuna, marlin, sailfish, sharks, and other finfish that Steinbeck and Ricketts had seen only seventy years earlier.
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The Gulf of California was not the only place experiencing ecological change due to low-oxygen waters. Beginning in 2002, low-oxygen water from off the North Pacific shore had slipped up over the continental shelf and moved inshore, killing off bottom-dwelling marine creatures off the coast of California, Oregon, and southern Washington. Gilly and others have been watching these findings, too. These low-oxygen events normally arrived in the late-summer months.
In 2006, Pacific waters off Oregon went into an anoxic (no oxygen) condition, killing off many organisms. Submersible vehicles put into the water recorded dead fish strewn across the bottom. Surveys revealed near complete mortality of bottom-dwelling creatures. Continental shelf waters off the Pacific Northwest are from twenty to fifty miles across. They lie beneath the California Current, which is one of the richest marine ecosystems in the world, though this system will be in jeopardy if low-oxygen events grow in size and frequency.
Waters flowing south along the shore tend to bank clockwise in the northern hemisphere and counterclockwise in the southern hemisphere, an effect caused by the rotation of the earth on its axis. Off the US Pacific coast, prevailing northwest winds push surface water away from the coast, and cold, nutrient-rich waters at depth are pulled up to replace it. This greatly increases the productivity of coastal marine environments.
Though many fish stocks are down off the California coast, marine mammals are doing well. Part of this may be the result of their adapting to consume squid and other creatures in the deeper sea. To get to these depths, whales, dolphins, seals, and sea lions all had to pass through a unique event in evolution. In prehistoric times, ancestors of these mammals came out of the sea as fish, lost their gills, and evolved lungs to breathe air. But they returned to the sea when competition from land animals increased, and they had to learn to survive underwater again, only this time breathing air. They currently use a host of neat breath-holding tricks, since the deep ocean is not a friendly place for air breathers. Gilly says that studying sperm whales is difficult, so scientists study other diving marine animals as proxies for whales.
Back in the 1960s, scientists generally thought animals might dive to 325 to 650 feet (100 to 200 meters), but researchers at the Scripps Institution of Oceanography in San Diego, California, recorded a Weddell seal in McMurdo Sound off Antarctica that dived to 1,970 feet (600 meters).
Since then, emperor penguins, leatherback sea turtles, northern elephant seals, bottlenose whales, and sperm whales have met and surpassed that record. In a world where the oceans may no longer hold enough oxygen for gill-breathing fish, breath holders might still have a chance at survival.
Elephant seals are a great example of an adaptable breath-holding mammal. And since they come out of the water only twice a year for extended stays, they are a lot easier to follow by attaching tags and transmitters while on land in order to record dives. Northern elephant seals have recovered from near extinction and number nearly one hundred thousand animals in the North Pacific. They utilize a unique set of evolutionary adaptations on their deep dives. Their heart rates at the surface are about 120 beats per minute, but while diving they can reduce that to 30 to 35 beats. They have even been recorded as low as 2 beats per minute—the edge of cardiac arrest in a human. Unlike man, most of the oxygen in diving elephant seals is stored in myoglobin in the muscle and hemoglobin in the blood instead of the lungs. They have higher concentrations of hemoglobin in the blood and larger blood volumes than most animals.
Elephant seals have streamlined bodies that glide through the water as if they were traveling on a layer of ball bearings. In a paper in Nature in 2011, biologists at the University of California, Santa Cruz, reported that one elephant seal dove to 5,765 feet, then a record for the species. That’s the equivalent of more than three Empire State Buildings stacked on top of one another, with the seal plummeting from the top of the uppermost building to the basement of the bottom building before coming back to the surface, a distance of over two miles. Aside from the two or three months of the year that they come out on land to mate or to molt, they are mostly underwater, not really a diving animal but more of an animal that occasionally surfaces.
All the elephant seal’s air passages, including the lungs, collapse flat and become airless between 350 and 700 feet (100 and 200 meters). With no air in these spaces, there can be no exchange of gas (particularly nitrogen), and thus elephant seals avoid the blood chemistry imbalances such as the bends (nitrogen bubbles) and rapture of the deep (nitrogen poisoning) that plague human divers.
On these dives, the elephant seal’s face looks like a prune. Researchers like to paint up Styrofoam mannequins, put lipstick on them, color their eyes, and send them down 300 feet just for kicks. They come back looking like shrunken heads. But the dives are worth it to the elephant seals, said University of California biologist Burney Le Boeuf: “The deep-scattering layer, the top of the oxygen minimum zone, is where most of the biomass in the ocean is concentrated. These animals are diving to the center of the richest part.”
But it’s dark down there. Cameras attached to these animals come back with images of a black screen. Some fish are bioluminescent, like lantern fish, a favorite of Humboldt squid in the Sea of Cortez. Whales and seals may swim below their prey and in daylight hours look back up at their silhouettes. The animals are well adapted for this territory. The enormous eyes of the elephant seal help it see in the dark. Whales may do one better than elephant seals, using natural sonar systems to locate their prey. The nose of the sperm whale constitutes a quarter to a third of its total weight and may contain the most powerful sonar system in the natural world.
Deep divers have a virtual monopoly on their prey at those depths, and they also avoid two deadly predators that spend most of their time at the surface: great white sharks and killer whales. For the most part, elephant seals are attacked when getting in and out of the waters on the islands they visit twice a year—for a month or two in winter to breed and for a month or less in summer to molt. They spend the rest of the year in the water on long northern migrations of up to thirteen thousand miles. They dive almost continuously on these trips, each dive lasting twenty minutes or more, after which they spend two or three minutes at the surface, taking in oxygen and letting out CO2, before they head back down. These are incredible adaptions for an animal that breathes air.
Without these threats, diving can be almost an autopilot affair. Sperm whales and elephant seals sleep as they dive, closing one eye while half of the brain naps and the other side keeps vigilant, then switching back and forth. Plus, once they get down to those depths, the escape responses of prey are a lot slower, allowing deep divers to wander around as if they were at an all-you-can-eat buffet.
But once again the remarkable Humboldt squid has another adaptation in its bag of tricks. Gilly worked on a study with biologist Julia Stewart and found that Humboldt squid, both off Monterey Bay and in the Gulf of California, sometimes power-dive to depths of up to one mile—right through the oxygen minimum zone—and remain there for long periods of time, sometimes all day, before powering upward again. This trick is possible because the oxygen minimum zone is really a layer, and oxygen starts going up again at depths of more than about 3,500 feet because of deep ocean currents that bring oxygen to deep waters. “These extraordinary dives by Humboldt squid may be escape responses triggered by the presence of groups of foraging marine mammals. The squid simply dive down, hang out for several hours, and then pop back up, hoping to find the predators gone,” says Gilly. Only squid seem to navigate these low-oxygen zones so effortlessly. Seals and whales have to come back up for air, but squid can move up and down without it.
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Most fish, however, are limited to shallower waters, where they are the target of marine mammals and man, the latter responsible for diminishing fisheries. According to the World Wildlife Fund, the Gulf is the source of nearly 75 percent of Mexico’s total annual fish catch, but overfishing (both industrial and artisanal) is contributing to dramatic declines in sharks, rays, and finfish. The global decline in fish catches, combined with rising demand, is leading to a global fishery crisis that threatens the Gulf of California as well as the rest of the world.
Humanity doesn’t limit its impacts to fish most commonly found on menus. Exotic sea creatures from turtles to manta rays to marine mammals are being hunted to extinction. Shark numbers, for example, have declined by 80 percent, with one-third of shark species now at risk of extinction. The top marine predator is no longer the shark; it is us.
It has been ten thousand years since most humans lived as hunter-gatherers. Fish are the last wild animals that we hunt in large numbers. And yet we may be the last generation to do so. On average, people eat four times as much fish now as they did in 1950.
In the late 1980s, the photographer George H. H. Huey and I went to the end of Baja to do a story on the shark fishermen there, who complained of fewer and smaller shark catches. When I interviewed a number of marine biologists about this, no one could imagine that these great open-ocean species could diminish. Even Rachel Carson couldn’t imagine fish stocks diminishing. But all that has changed.
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Humboldt squid could beat the odds against other marine creatures. Their numbers are expanding at sea, while ocean fish populations are contracting. In a relatively short period of time, this squid has learned to adapt to climate change and alterations of oxygen content in the water, conditions that are fatal for many other animals.
Gilly has a lot of respect for this animal: “If someone wanted to design an ocean predator for the future, this would sure be it.”
What evolutionary adaptations will we need to survive our future?