Monarch's first migration

Monarch’s long journey

One pup returns from a year at sea

Researchers don’t often put electronic tags on elephant seal pups. At more than $3,000 per satellite tag, losses are just too high to risk expensive technology. But in one case, it paid off big time. One tagged pup not only survived, she returned with new and exciting data. 

Photo taken under NMFS permit 27514.

The first migration

Elephant seals are migratory, swimming north along the coastline as far as Alaska and out into the northern Pacific. After pups are weaned, they remain on the beach for a month or so, building up their breath-holding and swimming skills. But they have nothing to eat after their mothers leave them. They live on the blubber they gained while they were nursing. Weaned pups make their first migration alone, without adult guidance. They leave the beach in the spring, and those that survive return in the fall.

Although pups haven’t been tracked on that first migration, the accepted wisdom was that they didn’t get as far as adults, to Alaska, on that first migration. Cal Poly Associate Professor  Heather Liwanag’s research set out to see how far they did go. They learned that while most don’t get that far, at least one did.

Pups tagged at Vandenberg and San Nicolas

Katie Saenger, one of Professor Liwanag’s master's students, tagged five pups at the Vandenberg Space Force Base beach and five pups on San Nicolas Island in April 2023. Their electronic tags allowed the researchers to follow the pups in real time.

Photo taken under NMFS permit 27514.

The researchers chose nicknames for the seals from local wildlife: Frog, Plover, Goby. Monarch’s name turned out to be especially apt. Monarch butterflies are also long-distance migrators.

Tracking that first migration

Nine of the pups stayed conservatively close, migrating along the California-Mexico coast. The team retrieved a device from one at King Range National Conservation Area, near Cape Mendocino in Northern California, and one from Año  Nuevo, north of Santa Cruz. Another was tracked to San Francisco Bay, but the beach he hauled out on in the Farallon Islands was inaccessible to humans.

One of the Vandenberg seals, Monarch, swam north and kept on going. 

Team members and other elephant seal observers watched her progress. Without guidance, pups somehow find their way. They don’t swim across the surface. They dive down and come back up, making forward progress. Females like Monarch may feed along the way, snapping up small fish.

Monarch swims, and swims

Watchers were excited to follow the signals coming from Monarch’s tracking device. She was doing so great! Going farther than previous research led them to believe pups would travel. Go, Monarch!

Her up-and-down zig-zagging indicated that she was finding food in those cold Alaskan waters. Out to the edges of the Aleutian Islands, nearly to Russia.

On October 5, 2023, after six months at sea, she turned south and headed for California. All seemed fine until October 26. Monarch’s transmitter went silent. The bad news for seal pups is, that usually means they met their fate in the jaws of a white shark. Thus goes the cycle of ocean life.

But it wasn’t. The transmitter's battery had failed, but Monarch hadn’t. She was still swimming back. A scientist taking a bird survey saw her on May 12, hale and hearty.

It’s Monarch!

Julie Howar, Senior Marine Ecologist and GIS Specialist from Point Blue Conservation, was performing bird surveys at Vandenberg when she saw two elephant seals wearing transmitters on their heads on the beach. One was this year’s weanling, Aurora, who had not yet left the beach after being tagged in April 2024. The other was a juvenile.

Photo by Julie Howar.

Identifying elephant seals is a challenge. Because they molt their skin every year, dyed marks fall away with the skin. This young seal had no dye marks, but she had a flipper tag that was partially visible. Dr. Howar used her spotting scope to take a photo. She was able to read a couple of digits on the seal’s flipper tag. She reported the sighting to Liwanag.

It was Monarch!

“It was amazing that Julie knew what to look for and reached out to me!” Liwanag said.

Surviving the first migration is significant, since only about half of the pups do. They usually gain little, if any, weight. Monarch went a step better: she gained 73 pounds. The fishing in Alaska was good.

“We were so excited when we figured out it was her,” said Liwanag. “She is the first seal to demonstrate that weanlings can go as far as Alaska, which we did not expect.”

Retrieving the data collection devices

Left to right: Molly Murphy (Cal Poly graduate student), Katie Saenger (Cal Poly graduate student), Kate Riordan (Cal Poly MS graduate), Dr. Heather Harris (TMMC), Liz Eby (TMMC), Dr. Heather Liwanag (Cal Poly), Lauren Campbell (TMMC), Elise Fiskum (Cal Poly undergraduate), Kenzie Davidson (Cal Poly graduate student), Rhys Evans (Biologist, Vandenberg Space Force Base), Jenna Camargo (Cal Poly undergraduate). Photo by Dave Clendenen.

The Cal Poly researchers pulled together a team to retrieve the devices on Monarch’s head and back. Master’s student Katie Saenger led the team, since Monarch is part of her thesis project. Liwanag and graduate student Maria Lopez-Neri joined her, along with veterinarian Heather Harris and veterinary technician Lauren Campbell from The Marine Mammal Center, and Vandenberg biologists Rhys Evans, Nick Todd, and Zia Walton.

“Accessing the beach at Vandenberg is always an adventure,” Liwanag said.

Todd is an experienced climber, skills he uses as an ornithologist specializing in falcons. He guided the group in setting up a rope to help them climb the bluff to the beach.

“The last part is especially steep, and it's best to move down backward -- not quite rappelling, but definitely not just hiking,” Liwanag said. “It is a challenge to get our team and all our gear down the hill (and back up!), especially with our heavy weighing gear.”

Photo by Molly Murphy

Weighing a seal involves a tripod with a scale. The seal is lifted in a tarp to be weighed. Nothing involving elephant seals is easy.

On the beach with the seal, The Marine Mammal Center veterinary team, Harris and Campbell, administered the sedative and monitored the seal while she was sedated during the tag removal. The amount of sedative needed is based on the seal’s weight. Monarch was cooperative enough that the team could weigh her before they gave her the injection. A safe dose calms the animal to allow researchers to handle her safely, without endangering the seal. It’s a delicate balance.

The zip ties were cut. Success! Devices in hand.

Analyzing Monarch’s data

Back at the lab, they downloaded the data. Preliminary results show that Monarch dove as deeply as 600m (2,000 feet), with many dives between 400 (1,300 feet) and 500m (1,600 feet) deep.

“These are impressive dive depths for a young seal pup!” Liwanag said.

Saenger’s master’s thesis project focuses on that first foraging migration of newly weaned northern elephant seals. The paths reported by the tracking devices map out where they travel, which can then be related to ocean factors that adult seals are known to use to navigate, such as sea surface temperature, the ocean floor, including the Alaskan coastal shelf and the seamounts along her return trip, and productivity.

“We simply don't know where these seals go on their very first migration, or how they decide where to go,” said Liwanag.

Other possible influences are whether the seal is born in a new or an established rookery, and whether they are male or female. Adult female and male seals migrate to different places, with different foraging strategies.

“We know the adults have very different migration patterns between males and females, but we expect that these differences may not be as pronounced at this age.” Liwanag said. “So far, we see that there is a lot of individual variation in migration patterns. This makes sense, because the seals have to find their own way with no instruction from anyone. They don't learn from their mom, and they don't travel together.”

Asleep on the beach

After removing the devices, the team watched over Monarch until she recovered from the sedative.

“Monarch moved back near her original napping spot and seemed to be doing just fine,” Liwanag said.

Welcome back, Monarch.

Activities conducted and photos taken under NMFS permits 22187-04 and 27514.

Satellite and VHF tags

The pups get satellite and Very High Frequency (VHF) radio transmitter tags.

The satellite tag is zip-tied to a polyester mesh glued to the seal’s head with marine epoxy.

The satellite tag on her head sends signals to the satellites when the seal comes up for a breath and her head is out of the water. The batteries on Monarch, and other seals in that 2023 cohort, ran out of juice and stopped transmitting. These young seals may be spending more time at the surface than adult seals, running the batteries down. The researchers adjusted for that possibility in 2024 by programming tags to transmit less frequently, extending battery life.

A VHF radio transmitter is zip-tied to polyester mesh on the seal’s back.

“We use that to home in on the exact location on the beach,” Liwanag said.  “We only want to hear that signal when the seal is completely hauled out.”

The polyester mesh patches will fall away as Monarch molts her skin.

“That’s why we hustled down there to retrieve her tags as soon as we could,” Liwanag said. “She was in the process of molting off those patches, and we were worried that the tide might take the tags away if she molted them onto the beach.”