“Hey Mike. Does this look like a sea lion or an elephant seal to you?” I was looking at some TOPP satellite tracks from September of last year when I posed this question to my officemate and TOPP colleague, Mike Weise. Mike works with male sea lions and I work with female elephant seals. Usually there are obvious differences between the satellite tracks of these two species, with sea lions remaining in the coastal zone and elephant seals traveling great distances out into the North Pacific Ocean. But in this case a very different picture was emerging. One seven-year-old female that we had tagged in May 2005, began her migration in an unusual way, heading south towards Point Conception and the Channel Islands.

A Hair-raising Track
At that time of year we select animals to tag based on hair length (so that the instruments will actually stay glued to the animal for the 8 months they’ll spend at sea) and body condition (skinny females are more likely to head to sea sooner). So ideally we want a skinny female with long hair. Female number 055 (the number on her flipper tag) had really long hair and was skinny, but when she headed south we began to wonder whether she had really molted or not. We worried that perhaps 055 had not shed her old coat, and was actually heading for a Channel Islands rookery to molt there. We were relieved when she started to head north again.

Dinner in Monterey Bay
However, as I continued to check on 055’s progress, she threw us another curve ball. Instead of heading west out into the Pacific as the vast majority of adult females do, she looped into the Monterey Bay where she remained for most of her 8-month foraging trip. She left the bay a few times, but each time she looped back to the same location and spent considerable time here. She was doing something very different than other female elephant seals, and her tracks were more like those Mike Weise has seen from adult male California sea lions. So we wondered what she might be feeding on, what her diving behavior would look like, and whether she would have gained as much weight as the other females upon her return in January to breed.

What a Difference a Dive Makes
On January 5th, 2006, 055 returned to Ano Nuevo, and we recovered her instruments about a week later. From her time-depth recorder (TDR) we learned that her diving behavior was very much like all the other elephant seals. Her deepest dive reached 1,401m (4,620 ft.) and lasted 39 minutes. Her longest dive was over an hour and reached a depth of 846m (almost 2,800 ft.). By comparison, the maximum dive depth recorded by TOPP researchers for an adult male California sea lions is 475m (over 1,500 ft.)—which was 055's average depth, and the longest California sea lion dive on record lasted 12.1 minutes. Although 055's track looked like that of a sea lion, she showed her true elephant seal colors with her diving behavior. So, although you can see the differences between these two species clearly on the beach, sometimes you have to dive beneath the surface to spot their differences when they are at sea.

Sometimes it Pays to be Different
Watching 055’s story develop we also wondered how well she would do with this unique strategy. When we weighed her in January she had gained a whopping 200kg (440 lbs). But she still leaves us with questions: why did she behave the way she did (we suspect she might have been feeding on a new influx of Humboldt squid in to the bay, but a blubber sample I took will hopefully tell us more about her diet)? And as she was so successful, why don’t more elephant seals do what 055 did? The TOPP elephant seal team hopes to be able to answer these and more questions in the near future, stay tuned for updates on 055 and other female elephant seals.