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Tracking a Seal by Satellite

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Conservation | Education | Mammals

Wednesday, January 30, 2008


Back in the summer of 1999, a visitor watching our sea lions swim past the pinniped tunnel at the Aquarium of the Pacific mentioned to me that she had taken a vacation up to Hearst Castle recently and while there had seen elephant seals resting on the beach. She noticed that a few had faded orange tags on their flippers and that one of the seals had a tag that read 3709. The number sounded familiar so I looked it up in my records. It was quite a revelation. The seal that the woman saw on the beach was Mac, an elephant seal that I helped track by satellite two years before. I thought it might be cool to share with everyone the details of Mac’s voyage that year.

Curiosity is a wonderful trait to have. In 1997, a year before I joined the Aquarium of the Pacific, my curiosity led me to explore ways of finding out what the elephant seals that I had helped rehabilitate back then did after being released back into the wild. The solution I came up with was to track a seal using a satellite transmitter. I spent many months researching satellite-tracking devices, searching for the resources and paperwork to allow me to mount a tag on a seal and then helping to coordinate the project after a source was found.

To study the movement of rehabilitated elephant seals after release, on July 28, 1997 a yearling seal treated at the Marine Mammal Care Center at Fort MacArthur, was released off Catalina Island bearing a then state-of-the-art satellite tracking and TDR (Time and Depth Recorder) device on his back. The device would transmit a signal to a grid of orbiting satellites whenever the seal surfaced that gave the animal’s position, time spent underwater and depth that he reached during his dives. The satellite tag, which was funded by the educational Website WhaleNet, was attached to the seal’s back by a biologist from the New England Aquarium using a special mount and adhesive. The device would not be a permanent fixture. The seal would shed the mount during his next annual molt. Seal number 3709 just did not seem like the right name for an animal that was to become the star of a scientific research project that would be followed by school kids across the country and around the world via a special website that allowed students to track the seal, so my wife Pam, a 4th-grade teacher, came up with the critter’s official name. He would be known as Mac (as in Fort MAC-Arthur). Before this project, most elephant seal tracking research had been done on animals from Ano Nuevo, near Santa Cruz. Mac would be the first elephant seal tracked from Los Angeles waters.

Mac was an ideal subject for the project. He was a yearling animal, which meant he had the survival instincts to make it through a year in the dangerous ocean. He showed those instincts when he immediately dove for the bottom the moment he was released. A surfaced seal is a prime target for prowling sharks. After Mac was released it took me awhile to calibrate the readings from the satellite. For the first few days, my interpretation of the downlinks had Mac headed toward Las Vegas! I either had my numbers wrong or the seal had a yearning to play the slot machines on the Las Vegas Strip! When I finally corrected my calculations (as my wife Pam would say “See, math is important!”) and had him positioned in the ocean, I was amazed to find that Mac was making some remarkable dives in the waters beyond the San Pedro Channel. Although most of his dives were in the 10- to 15-minute range, every so often he would make a really long dive of well over an hour. The young seal’s dives became deeper and deeper as his voyage continued. Several times he dove beyond a thousand feet. That’s deeper than most Navy submarines can go. One of the interesting observations was that Mac’s longer dives were relatively shallow, in the 100- to 600-foot range.

After release, Mac made a beeline westward toward the open ocean. He traveled over 200 miles out to sea. He then headed back toward the coast, encountering land near Vandenberg Air Force Base. After hugging the coast north, Mac spent a few days off San Simeon, near the elephant seal rookeries at Pietros Blancos. He then continued his journey northward to Monterey Bay where he spent time wandering the bay, zigzagging his way from the southern end near Monterey to the northern end near the elephant seal rookeries of Ano Nuevo, and back. These waters are part of the area known as the Red Triangle where seal-eating great white sharks prowl. I was a bit concerned about Mac’s well-being when he spent several weeks in the bay. However, experienced elephant seals are like stealth bombers, extremely capable of evading the radar of prowling sharks by staying deep. It was in the abyss of the Monterey Bay submarine canyon that Mac made his deepest dive. One that took him past 1,500 feet! Elephant seals dive deep for their food, which consists of deep water fish and squid species. Some elephant seals have been recorded diving over a mile down, while others have stayed submerged for nearly two hours! In comparison, California sea lions like the Aquarium’s Parker and Miller generally dive for only a few minutes and reach depths of merely a few hundred feet.

By the time Mac decided to head back south, his satellite tag had been transmitting for over two months and had survived thousands of pounds of water pressure. Good signal fixes and data were becoming harder to come by. Mac’s last “sighting’” put him off San Nicholas Island on Oct. 10th 1997. At that time there was fear that perhaps the wandering seal had encountered a hungry great white shark or killer whale, but after three days of silence, the satellite received a faint signal from Mac. It wasn’t enough to get a position fix, but it was enough to let us know that the transmitter had resurfaced for a short while. It was as if Mac wanted to send one last transmission to let us know that he was still out there.

Two years later a visitor to the Aquarium of the Pacific would confirm that Mac’s voyage though the Pacific had indeed continued.

Tracking a Seal by Satellite
A map of Mac's travels in 1997.  | Hugh Ryono
Tracking a Seal by Satellite
A Northern elephant seal sleeps on the beach at Puertas Blancas near where Mac was seen by a visitor to the Aquarium of the Pacific two years after his satellite tracked journey in the Pacific.  | Hugh Ryono
Tracking a Seal by Satellite
Mac was a rehabilitated yearling elephant seal that was treated and released much like this one being returned to the wild.  | Hugh Ryono
Tracking a Seal by Satellite
Elephant seals are a fascinating species. Here a elephant seal pup turns a curious eye toward my camera underwater. These seals can stay underwater for nearly two hours and can dive more than a mile down.  | Hugh Ryono

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