The annual Cape fur seal pupping season
With November and the start of the annual Cape fur seal pupping season fast approaching, members of the public can once again expect to encounter many carcasses washed up on Plett beaches.
Preliminary research suggests that up to 45% of Cape fur seal pups that are born on Robberg Peninsula drown in the first month of their lives as a result of large swells.
Such high rates of mortality prior to weaning are not unusual in fur seal pups. Displacement and drowning due to rough weather have been identified as one of the main natural factors causing high levels in Cape fur seal pup mortality at other breeding colonies along the south coast of South Africa and has also been recorded in a number of seal species in other parts of the world.
Young Cape fur seal pups cannot swim very well and are born with a black coat not yet insulated for survival in the ocean. They spend the first 3 months of their lives in a rookery among the rocks and boulders of Robberg Peninsula’s north shore while suckling rich milk from their mothers.
While waiting for their mothers to return during short foraging trips to sea, they form large crèche’s close to the water’s edge. Here many get swept away from their rookeries – particularly during periods of high easterly wind and swell notoriously common in summer. Most drown and wash up on the mainland, especially on Robberg beach, but a few live ones are sometimes rescued by passionate individuals and then later returned to the colony by local tourism operators.
During previous seasons up to 600 newborn pup carcasses were recovered along Plett beaches. In contrast, only around 50 carcasses from older age classes (i.e. yearlings, subadults, and adults) wash up each year, mostly between November to May with a peak in January. Although the majority of these carcasses wash up in an advanced state of decay, there are necropsy (animal autopsy) records for a number of fresh carcasses which reports on various usual and unusual causes of mortality and secondary symptoms.
These include shark-inflicted bite wounds, stingray-inflicted spine wounds, parasitic infestations, entanglement in fishing gear and plastics, and shot seals. For those that were fresh enough to collect pathology, samples are stored at the Port Elizabeth Museum until funding becomes available for expensive investigations into toxicology and the presence of disease and virus.
It is worth mentioning that breeding season is a very stressful time for adult seals, especially older males who lose body condition as they spend a lot of energy fighting each other to establish and maintain breeding territories.
It, therefore, comes as no surprise that over 90% of adult carcasses recovered along Plett beaches during past breeding seasons belonged to large males. Recently weaned yearlings are also known to struggle at this time as they learn to find their own food in order to make the transition to adulthood.
You can help by reporting seals on the beach, dead or alive, to the Plett Stranding Network on 079 463 4837.
The network includes seal researchers, voluntary rescuers, local rehab, and carcass disposal authorities. Sometimes carcasses are marked with bright spray paint to indicate that they have been sampled for research, and these need not be reported again.
For more information on this and other Plett seal research projects, you can visit our website or follow our Facebook page.