Fat Fur Seal Pups at the Farallon Islands
November 21, 2024
by Jim Tietz, Farallon Biologist
For humans, putting on a few extra pounds around the holidays is not always desirable and can occasionally be unhealthy. Northern fur seal pups, though, need to put on as much weight as possible before their moms wean and abandon them. At the Farallon Islands, northern fur seals typically give birth to their pups in July. The moms then have 4-5 months to fatten them up before weaning them in November and December. After weaning, the pups may remain at sea for 2-3 years before returning to breeding islands. A fat pup is a healthy pup!
During years when food is scarce, such as during severe El Niño events, females may abandon their pups to ensure their own survival. Pups may also be abandoned during years of Harmful Algal Blooms (HABs), or toxic red tide, which sickens or kills the females. This year, a HAB occurred off Southern California that may have caused the premature abandonment of many fur seal pups at San Miguel Island resulting in their deaths. We worried that this might also occur at the Farallones.
On August 13th, we counted 1,276 pups from the Farallon Island’s lighthouse, which was a record-high pup count for Point Blue from this location. Two hundred years ago, there were over a hundred-thousand fur seals on the island, but they were eradicated in the early 1800’s for their pelts which were sold to China. In 1996, we documented that fur seals were once again breeding on the Farallones, and their population has been growing exponentially ever since.
A couple months after the pups are born, they become more mobile and spend more time in the nearshore water where they play and wait for their moms to return from their foraging trips. From the lighthouse, where we conduct our weekly pinniped (or seal and sea lion) survey, it is not possible to identify the age of the pups that are in the water, and we cannot see their body condition. However, on Nov 10th, we took a trip to West End Island and counted 1,074 pups on land, and we estimated another 400 in the water. The pups on land appeared fat and healthy. This is a great sign that survival this fall was high and that there should be good recruitment into the colony in future years. On Sep 19th and 20th, we tagged 132 fur seal pups to track their survival and recruitment in future years. Without Point Blue’s year-round presence on the island, this information would not be known.
Since 1968, we’ve been conducting research on this National Wildlife Refuge, in partnership and close collaboration with the US Fish and Wildlife Service. We document population dynamics, diet composition, and reproductive success of 13 seabird species, 5 seal and sea lion species, and white sharks. Explore more of our Farallones work on this blog or here. And consider becoming a Steward of the Farallon Islands.