Elephant seals are pouring into Año Nuevo State Park Natural Preserve and Point Reyes National Seashore. The great white sharks will follow them in. Sea otters are going on a vigil to avoid becoming shark mints.

This wildlife phenomenon with elephant seals, great white sharks and sea otters right now shows how everything is connected in nature. This story started nearly 50 years ago with the Marine Mammal Protection Act. Many of the outcomes can be seen this weekend and into winter on the coast of the Bay Area and Monterey Bay.

Elephant seals

At Año Nuevo, no elephant seals were present in 1955, and the first pup born here was believed to be in the 1960s, according to park staff. The low numbers were a remnant from the days of commercial slaughter, when elephant seals were hunted to near extinction to be processed for oil.

This week, about 300 elephant seals are on the mainland peninsula just offshore at a small island. As the annual migration hits full swing, those numbers are likely to reach 500 by early November and 3,500 by January. Starting in midwinter, pups, which average about 75 pounds, will be born, reared and taught to swim and feed.

If you want to go Elephant seals: 3-mile guided walk is routed amid elephant seals during breeding season; $7 per person, Dec. 15 through March 31, reserve at www.reservecalifornia.com. Contact: Año Nuevo State Park Natural Preserve, Pescadero, 650-879-0227 or 650-879-2025, www.parks.ca.gov. Great white sharks: Great whites occasionally sighted on whale watching trips to Southeast Farallon Island; $135 per person, free parking at Marina Green in San Francisco. Contact: Oceanic Society, 415-256-9604, www.oceanicsociety.org. Sea otters: Sea otters can be sighted along slough that leads to mouth of Moss Landing Harbor, and east of Highway 1 in estuary; GPS location: 2370 Highway 1, Moss Landing. Contacts: Kayak Connection, kayak rentals, 831-724-5692, www.kayakconnection.com; Elkhorn Slough Safari, pontoon boat tours, 831-633-5555, www.elkhornslough.com; Blue Water Ventures, guided kayak tours, 831-459-8548, www.bluewaterventures.org.

Read More

At the same time, elephant seals are arriving to Drakes Beach and the vicinity of the Chimney Rock Headlands at Point Reyes National Seashore and the Southeast Farallon Island.

To put it in perspective, the population was estimated at about 100 animals in 1890 on the Pacific Coast and then 30,000 in 1970, according to a scientific document published in 1972 in the Federal Registry. Since the MMPA became law, the population has grown to about 160,000.

During last winter’s 35-day federal shutdown, so many elephant seals showed up at Point Reyes that they took over the parking lot at Drakes Beach, an amazing sight. The Southeast Farallon has become a significant breeding site, which, along with high numbers of sea lions and harbor seals, has helped draw in great whites.

At Año Nuevo, the arrival of elephant seals has become an event that attracts about 50,000 people every winter. Guided walks that range about 3 miles are routed along roped-off paths to see the behemoths, where the males can range to 20 feet and 5,000 pounds and collect harems of females. Parking is $10 per vehicle and tours are $7 per person.

Great white sharks

In the 1990s, every sighting of great white sharks off the Bay Area coast was treated as a phenomenon that often hit the front page of The Chronicle and led local television newscasts. At the time, the best estimate that about 200 to 400 great whites roamed the Gulf of the Farallones.

That number is now 2,400, according to a study released earlier this year, and explains the growing number of sightings and encounters.

One of the wildest stories of the year was at Mavericks, located near Pillar Point Head on the San Mateo County coast. Drake Stanley, who runs a tow and rescue service with a personal watercraft, sighted a great white estimated at 16 to 18 feet long that appeared to be trolling the big-wave surfers. At one point the shark swam directly under him and within 30 yards of a surfer. Stanley jetted the PWC at the shark, diverted it from the surfer, and then ferried nine surfers to shore.

It’s been well reported that the increase in marine mammals has likely led to a corresponding increase of great whites. With more elephant seals, sea lions and harbor seals, there’s more food, of course, for Ol’ Whitey.

The population expansion of both marine mammals and sharks is a coastal event. On the central coast, 17,000 elephant seals have been counted at peak near San Simeon (San Luis Obispo County). To the south at Montaña de Oro State Park, a surfer was attacked and survived two wounds that required 50 stitches.

With plenty of food available, it’s virtually a sure thing that great whites will arrive this month at their favorite haunts: the Southeast Farallon Island, Año Nuevo, the Marin Coast off Stinson Beach, the vicinity of Chimney Rock at Drakes Bay, and the mouth of Tomales Bay.

Sea otters

The recovery of the sea otter population has stalled just below the threshold of being delisted under the Endangered Species Act, and marine biologists believe that it’s likely great white sharks are the limiting factor. A sea otter, at about 4 feet and 60 pounds, is sized just right for Mr. Toothy.

Like so many wildlife species in the 1800s, commercial interests massacred sea otters to near extinction; about 150 were discovered by accident in the 1930s at a nursery area near Bixby Creek at Big Sur. Recently the population topped 3,100 for four straight years, making them eligible for delisting under the ESA.

Caution to pursue that proved correct. The latest survey counted 2,962 sea otters, below the threshold level (3,090), according to data released by the California Department of Fish and Wildlife.

A limiting factor to otter recovery is “shark bite mortality,” according to Linda Carswell, the southern sea otter recovery coordinator for the U.S. Fish and Wildlife Service. Shark predation could “limit their ability to expand into areas where they historically thrived,” she said.

One way otters continue to adapt is by migrating into coves and sloughs where they can avoid great whites as well as the brunt of winter storms, such as in Elkhorn Slough at Moss Landing. It’s common for about 70 to 80 otters to spend winter and spring here. You can often see them by kayak in the slough and estuary, or on foot from the adjacent Moss Landing jetty.

The MMPA helped grow the numbers of elephant seals, harbor seals and sea lions. That led to more food for great white sharks, and in turn, much higher numbers. That caused higher predation on sea otters. Like nearly everything in nature, every critter is connected to another.

Tom Stienstra is The Chronicle’s outdoor writer. Email: tstienstra@sfchronicle.com Twitter: @StienstraTom