06/09/2026
Amazing animals . . .
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A female northern elephant seal tagged at Año Nuevo Island off the California coast dove 5,788 feet on a foraging trip near Vancouver Island. Over a mile straight down, on a single breath, in water so deep and so dark that no sunlight has reached it in the history of the ocean.
She came back up, breathed for a few minutes, and dove again.
Northern elephant seals do not hunt the way most marine mammals hunt. They do not chase fish through sunlit water near the surface. They leave their California rookery, swim thousands of miles into the North Pacific, and spend months diving continuously to depths where the pressure would crush a submarine's hull and the temperature sits just above freezing.
They hunt squid and deep-water fish in absolute darkness using senses that researchers still do not fully understand. Then they surface, take a few breaths, and go back down. They do this around the clock, averaging sixty to eighty dives per day, spending roughly ninety percent of their time underwater. An elephant seal at sea is almost never at the surface. The surface is where it breathes. Everything else happens below.
Most females from the Año Nuevo colony forage in a broad zone across the northeastern Pacific, diving to average depths of around 2,000 feet. The record-holding female is an outlier. Instead of heading into the open Pacific with the rest of the population, she travels north along the continental shelf to the waters near Vancouver Island, where she pursues bottom-dwelling prey along the seafloor. Her dives go deeper because the prey she targets lives deeper, and the seafloor off Vancouver Island drops steeply into submarine canyons that most air-breathing animals have no business entering.
Patrick Robinson, the UC Santa Cruz researcher who analyzed her data, noted that the same seal dove even deeper on a subsequent foraging trip, pushing the record past 5,780 feet. She was not driven to that depth by desperation. She returned to the same foraging area and repeated the behavior across multiple trips. The depth is a choice, refined by experience, repeated because it works.
The physiology that allows this is extreme even by marine mammal standards. Before a deep dive, an elephant seal exhales. It goes down on empty lungs. Diving on full lungs would be fatal because nitrogen under pressure dissolves into the blood and causes decompression sickness on ascent. By collapsing its lungs deliberately, the seal avoids nitrogen absorption entirely. Its rib cage is flexible enough to compress under the water pressure at depth without breaking.
Its spleen stores oxygenated red blood cells and releases them into the bloodstream during the dive like a biological scuba tank. Its muscles are loaded with myoglobin, a protein that binds oxygen and releases it slowly during sustained exertion. Its heart rate drops from roughly a hundred beats per minute at the surface to as low as three beats per minute at depth.
The animal shuts down every system it does not need and routes all available oxygen to the brain and the muscles required for hunting.
At 5,788 feet, the pressure is roughly 175 times what it is at the surface. The water is between 34 and 39 degrees Fahrenheit. There is no light. The seal is hunting by sensing vibrations, pressure changes, and possibly bioluminescence from the organisms around it. It catches its prey, begins ascending, and reaches the surface minutes later to take a few breaths before the next dive. The surface interval is short because every minute at the surface is a minute not feeding, and a female elephant seal on her post-breeding foraging trip needs to regain roughly a third of her body weight before returning to the rookery.
Every elephant seal at Año Nuevo descends from fewer than twenty animals that survived commercial slaughter in the 1880s. The species was hunted for blubber oil until it was considered extinct. When a small colony was finally discovered on Guadalupe Island off Baja California, some of the naturalists who found them killed most of the survivors for museum collections.
The animals that remained, possibly as few as twenty, rebuilt a population that now numbers over 210,000 across rookeries from central California to Baja. Every seal on the beach at Año Nuevo carries the genetic bottleneck of that near-extinction in its DNA, and every one of them dives to depths that most humans cannot reach in a machine.
Source: Robinson et al. (2012). PLoS ONE. / UC Santa Cruz Elephant Seal Research Program / Bay Nature / UC News.
