Over the last few weeks, newborn Cape Fur seal (Arctocephalus pusillus pusillus) pups have been washing out on Robberg beach; most already dead, but a few lucky ones making it ashore alive. Cape fur seal pups are born between mid-November and the end of January. They are born with a black natal coat which insulates the pups and prevents them from overheating during their first few weeks when they are mainly ashore and exposed to intense solar radiation and high temperatures for long periods of time. Unlike the coat of adult Cape fur seals, this natal coat is not water-repellent and loses its ability to insulate pups when wet, resulting in significant heat loss in cold conditions. Furthermore, pups of less than 5 weeks old, while being able to float in water, are not really capable of swimming.
Stormy conditions, therefore, pose a risk to these newborn pups. In Plettenberg Bay, the Cape fur seal colony on Robberg Peninsula is protected from big swells approaching from the south-west. However, strong easterly winds bring big swells into the bay which wash into Robberg Peninsula’s eastern side where the colony is situated. When these strong easterly winds coincide with spring high-tides, fur seal pups are especially vulnerable to being washed off the rocks at the colony. Once in the water, pups quickly become hypothermic and drown, and currents carry them away and onto our local beaches.
Once ashore, live and dead pups are quickly discovered by members of the public and reported to relevant authorities. Since November, over 60 pups have washed ashore on Robberg beach. Four of these came out alive and were collected by members of Plettenberg Bay’s Stranding Network, a branch of Port Elizabeth Museum’s stranding unit, and taken to Tenikwa for rehabilitation. Here, they are treated for dehydration and any wounds they may have attained. Each pup is also tagged with a uniquely numbered flipper tag and has some of its fur and whiskers collected for genetic and diet studies. After a few days the pups are ready for release and are transported back to the colony by Offshore Adventures. Dead pups are also of interest to local stranding biologists. Freshly deceased pups are collected for full dissection at a later date where numerous samples are collected for morphological, diet and genetic studies. More decayed pups are sampled on the beach for genetics, fur and whiskers.
The next potential pup strandings are likely to occur around the following spring high-tides between 30 December and 6 January, 16 and 21 January, 29 January and 5 February, and 15 and 21 February, especially if easterly storm events occur during these periods. Luckily, after three to five months after being born the pups will have moulted their natal coats and acquired their adult coats. These adult coats will keep them insulated from the cold marine environment and they are then capable of swimming, such that they are no longer at risk during such storm events. As a member of the public, you can make a valuable contribution by reporting any live or dead seals, as well as other marine mammals, directly to the Plettenberg Bay Stranding Networks’ coordinator, Dr. Gwen Penry, on 072 817 7979, Offshore Adventures on 082 829 0209, Cape Nature on 044 533 2125, or Beach Control on 044 501 3125. Also, be sure to look out for upcoming articles by local marine mammal biologists in the CXPRESS to learn more about marine mammal strandings in this area.
Written by Danielle Conry
For further reading:
- ERDSACK, N., DEHNHARDT, G. & HANKE, W. 2013. Coping with heat: Function of the natal coat of Cape fur seal (Arctocephalus Pusillus Pusillus) pups in maintaining core body temperature. PLoS ONE 8(8): e72081. doi:10.1371/journal.pone.0072081.