Translocations: science with some plot twists

The anticipation I felt was more than I expected—every couple of hours I was logging into the Argos system database to check the latest satellite hits. Where were my seals going?

Earlier that day:

As a first-year graduate student in The Costa Lab at UC Santa Cruz, I was conducting my first field experiment with juvenile elephant seals (research performed under NMFS permit #19108 and IACUC approval).

Arriving just as the sun is rising at Año Nuevo Reserve to pick up two juvenile elephant seals for my translocation study. Each seal will be placed in the cages shown to facilitate transporting it and to keep both the seal and researchers safe.

After finding two healthy juveniles that had not yet started to molt, we safely got them into the cages and brought them back to Long Marine Lab at UCSC’s Coastal Science Campus. There, the seals were instrumented with heat flux biologgers that were custom-built by Wildlife Computers (Redmond, WA) following an earlier heat flux biologger designed and built by Dr. Markus Horning and used by his graduate student Kate Willis on Steller sea lions at the Alaska SeaLife Center. These Wildlife Computers biologgers were originally built for a research project on Weddell seals in Antarctica, but we refurbished and reconfigured them for my project.

The biologgers measure heat flux using small disc sensors (made by Concept Engineering, Old Saybrook, CT), which tells me how much heat is transferred between the seal’s body surface and its environment as the seal swims back from Monterey to Año Nuevo. This data would allow me to investigate the question: how do marine mammals thermoregulate while balancing their physiological adaptations for diving? Read more about why this question drives my research interests and why I’m using heat flux biologgers here.   

By lunchtime, both seals were equipped and ready to go! We loaded them up again on the flatbed truck and drove down to Monterey where we released them back into the bay. Click here to see a map of a translocation.

Each seal was equipped with the following tags: a satellite tag on the head (transmits location to Argos and includes an external temperature probe to measure water temperature), the heat flux biologger on its back with two surface-mounted heat flux sensors on its right lateral side (sensor near fore flipper visible in this picture), and right behind it a VHF tag (to facilitate finding the seal once it’s back on land). We decided to test out both CobanTM adhesive bandage (beige) and KT Tape® (blue) for securing the heat flux sensor wires.
Both juveniles—equipped and ready to collect data—were released on a beach at the southern end of Monterey Bay. (Translocation performed under NMFS permit #19108 and IACUC approval.)

With nothing to do until the animals came back, that is how I found myself spending the waiting game–compulsively checking the transmitted satellite locations on the Argos website. This translocation paradigm with juvenile northern elephant seals has been used by many researchers over the years to study the physiology of a deep-diving marine mammal over short at-sea trips. How do we know they will come back? Well, the seals must return to land to molt, and generally, they swim across Monterey Bay and return to their home colony Año Nuevo in a couple of days. So there I was, hoping each time I hit refresh I’d see a perfect line of dots showing my seals were heading home.

The map shows the sequential Argos satellite hits, where the colors represent the accuracy of the location estimate based on the Argos location classes (red: no accuracy estimation, orange: >1500 meters, yellow: 500-1500 meters, green: 250-500 meters, blue: <250 meters). The satellite tag on the juvenile’s head will attempt to send messages to the Argos satellites orbiting in space any time the animal returns to the surface and pops its head out of the water to breathe. The more messages the tag sends, the better the location estimate. However, seals usually don’t spend enough time at the surface to allow for the transmission of sufficient messages, so most hits are poor quality, which explains the impossible hit on land. But it still gives us a sense of where they are and when to expect them back at Año Nuevo.

The first seal (a.k.a. Obedient Juvie) returned to Año Nuevo in less than 3 days, which is pretty consistent with how most translocations go. But the second juvenile had a different plan…

Instead of heading back north to Año Nuevo, it wandered down south. After a couple of days of checking in on its status multiple times a day, I began to doubt whether this juvenile would ever come back home! While the satellite tag transmits information on the seal’s location, the heat flux biologgers are archival tags and must be recovered to obtain the data. While unusual, the juvenile could decide to not come back, or worse, it could become shark food—yikes!

That would put a new spin to ‘the dog ate my homework’ excuse. In this case, if we stopped getting satellite hits, my advisor would probably believe me if I told him a shark ate my data. As the days went by, I became more concerned I would not be able to get the data back—that is, assuming the sensors even stayed on and successfully recorded data—and the (very expensive) tags would be lost forever. But I kept telling myself to be patient and keep calm since we were still getting a few satellite hits per day. After spending 8 days out at sea swimming about (literally in circles at times), the juvenile finally decided to haul out!

The path of “Curious Juvie”

But as you may have noticed from the map, Curious Juvie—who earned that nickname after day 5 at sea—did not come back home to Año Nuevo. Instead, it decided to visit another elephant seal colony at Piedras Blancas, located about 3 hours south. So we made the drive down to go searching for Curious Juvie. Based on the latest satellite hits and using the antenna to pick up on the frequency emitted by the VHF tag, we were able to find our seal amongst its new friends at Piedras Blancas!  

Elephant seals lounging on a beach at Piedras Blancas, an elephant seal rookery south of Monterey.

Unlike the first juvenile, the heat flux sensors were no longer attached to its body. Seeing the sensors hanging from the cables, I wondered if they had stayed attached long enough to record any data. But having successfully recovered the tags, I would be able to find out soon enough!

Despite some unexpected (and nerve-wrecking) twists, my first two translocations were successful. Now for what every scientist gets excited about—downloading the data off the tags and, if data was successfully recorded, analyzing the data!

Written by: Arina Favilla, Graduate Student at University of California Santa Cruz.

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