By Sarah Teman
Science helps us adapt and improve. For decades, marine mammal stranding response and rehabilitation organizations in the United States have been treating and rehabilitating harbor seal pups, and releasing them back into the wild. It’s critical that during rehabilitation seals gain sufficient blubber and mass so their fat reserves can enable them to survive after they are released. Prior studies have suggested that seals with greater body mass have better odds of survival. Unfortunately, until now, there has been no nationwide assessment of the sizes at which seals are released.
As SeaDoc Society’s Research Assistant, I work alongside the Whale Museum to monitor the San Juan County Marine Mammal Stranding Network. I first became interested in the release size of rehabilitated harbor seal pups after interning with the rehabilitation organization Marine Mammals of Maine. I was so impressed with the hard work that goes into caring for seals I went on to intern for the San Juan County Marine Mammal Stranding Network before joining SeaDoc. I can’t believe I’m now publishing papers on this topic.
The Stranding Network responds to stranded marine mammals like harbor seal pups and provides scientific support to NOAA at the US federal level regarding diseases of marine mammals. But our work extends beyond this–we’re scientists after all!
After collaborating with the Vancouver Aquarium on a paper published recently that suggested heavier harbor seal pups released from rehabilitation had a higher change of survival, we began wondering what was going on with body condition and size of released harbor seal pups around the country.
Was it uniform? Did it vary year by year?
So, last year we teamed up with scientists from NOAA Fisheries and the California Academy of Sciences to take a look. We used long-term data collected by stranding networks and rehabilitation facilities to assess variation in seal body size and condition prior to their release. The study, recently published in the journal Aquatic Mammals, provides comprehensive and important baseline trend data on the sizes of rehabilitated harbor seal pups released all over the United States. This is an important to first step for understanding how body size and condition may affect post-release survival of these seals.
As it turns out, weight alone might not be the best criterion for understanding seal size, as two different seals of the same weight but different lengths could have different body conditions. Plus, seals have very flexible necks and can retract or extend them easily, making a precise length measurement difficult hard to obtain.
Watch this little guy squish up against the glass.
Figuring out a way to standardize length measurements, as well as incorporating additional measures of size into a body condition index, like girth or ultrasound measurements of blubber depth, could help us gain a more accurate understanding of harbor seal size pre- and post-release.
I anticipate that this study will be an important steppingstone for optimizing a body condition index for harbor seal pups prior to their releases.