Marion Island is home to two sympatric fur seal species, the Antarctic (Arctocephalus gazella) and Subantarctic (A. tropicalis) fur seals. At first glance, the untrained eye might find it difficult to distinguish between the females of the species. However, once you spend a little bit of time with them, you quickly learn that they have very different temperaments and actually look quite different from each other. The Antarctic fur seal (AFS) females are fiercely protective of their little ones and when approached, they will generally not move away but try to discourage you from getting too close by a surprisingly deep growl, often also moving in between you and the pup. They are surprisingly fast and one has to be very careful to read their body language and be ready to move away quickly if need be. The Subantarctic fur seal (SAFS) females however, have two strategies…number one is to growl and bark very unhappily (especially the older, more experienced females just lie there staring and growling at you), sometimes charging you to make sure you stay away. Strategy number two is to run like the wind (mostly the younger, inexperienced females), leaving the often startled and confused pup to fend for itself. One can always have another pup next year, right? The two species have very different lactational strategies, with the AFS and SAFS weaning their young at 4 and 11 months, respectively.
The males are however very easy to distinguish from one another. AFS males are huge, weighing up to 200kg. They are a beautiful greyish colour throughout. They also have a very deep growl that always makes me think of a tractor starting up. However, as uncomfortable as that growl can make you feel, their other vocalisation has the opposite effect…I don’t really know how to better explain it than the sound of someone trying to not sneeze too hard, put on repeat! It’s really something very characteristic of this species and once you’ve heard it, you’ll never forget it. It is a sound that always makes me smile! These big boys are also quite predictable with regards to their aggressive behaviour; they will warn you and if you don’t listen, they will charge. And boy, a charging AFS bull can make you run the 50m dash faster than you’ve ever dreamed possible! After you’ve seen these bulls fight each other (often resulting in serious injuries such as a broken jaw or even death), you really don’t want to get bitten by them. I used to call them the “Hulks” of the island. On the other hand, you have the SAFS bulls weighing in at around 160kg. They have dark brownish fur on the backs with a lighter, creamy fur on the underside of the body. These guys remind you of “Johnny Bravo” with all the swagger and the hairstyle too. During the non-breeding season they are generally quite skittish but once the testosterone levels rise a bit just before and during breeding season, they are extremely aggressive and dangerous because they have very unpredictable behaviour. Both of these species are highly territorial, making it impossible to access certain parts of a beach that they have claimed for themselves during the breeding season.
With the large number of animals currently calling Marion their home, it is difficult to imagine that in the earlier sealing days both of these species were hunted to near extinction in the Southern Ocean. Luckily they have been able to recover in the subsequent years. In recent years it has been noted, however, that the SAFS pup populations are declining, while the SAFS pup population are still increasing, albeit at a much slower rate. Reasons for this phenomenon is still unclear. Read more about this in the following article:
Wege et al. (2016). Trend changes in sympatric Subantarctic and Antarctic fur seal pup populations at Marion Island, Southern Ocean. Marine Mammal Science 32(3): 960 – 982. DOI:10.1111/mms/12306
The full scientific article can be obtained from the Journal of Marine Mammal Science or by contacting the authors directly.