Juvenile seals are filling the beach. The youngsters return in September and October for their annual haul-out. It’s four to six weeks of R&R for seals on the go.
The pups that were born in January and February show up, the survivors of their first migration. They are called young of the year, and are the smallest seals on the beach. Look for them among the older seals, up to 5 years old. The young of the year usually aren’t much bigger than the 200 pounds or so that they weighed when they left the beach in March and April. Surviving is the measure of success. They’ll put on weight later.
The seals at Piedras Blancas for the haul-out are generally not older than 5. Size alone is a good indicator of age, but check nose development on the largest seals. Males start growing that long appendage that gives them their name at about 5 years old, so it’s an indicator of size among subadults, and some of them may share the beach with their younger sibs.
Females don’t grow the nose, so it’s no way to tell on them. As adults, males are always larger than females, but until the male nose starts to grow, young males and females are difficult to tell apart. If you can see the underbelly, males have an additional dark spot, indicating the penis, below the umbilicus and two small teats.
Danger from sharks
August through March is shark feeding time along the coast. Juvenile seals make a good meal for sharks. They are big enough to satisfy without being as dangerous to the shark. Sharks attack from below and behind. A mature bull bitten by a shark on his tail end can turn around and bite the shark. Elephant seals are top predators themselves, with huge, sharp teeth.
“A big seal is still able to fight back,” said Taylor Chapple, shark scientist at Stanford University’s Hopkins Marine Station in Pacific Grove. “If you’re a shark and you lose an eye, it’s a serious consequence.”
Tomales Bay, the Farrallones and Año Nuevo are more popular shark feeding areas than Piedras Blancas, which became an established seal rookery only in the 1990s. Shark researchers checked on them two years ago, but found few sharks off this rookery.
Seals often show up at Piedras Blancas with healed scars or even open wounds from shark attacks, though.
Follow shark and seal migrations at www.gtopp. org. New technology, a wave glider, is being used to follow sharks tagged with acoustic tags.
Being at the top of the food chain, elephant seals also biomagnify mercury. A study released in September from UC Santa Cruz found mercury levels in the seawater at Año Nuevo during the time when seals shed their skin are 17 times the concentration of other coastal sites.
Another study found 99 percent of seals have blood mercury levels that exceed the threshold for clinical neurotoxicity in humans.
No one knows what the effects are on seals.
Seals, another canary in the coal mine of our oceans.