Harbor Seals in Marin County Hit Record Lows in 2024

A harbor seal mother and pup rest along Tomales Point, Point Reyes National Seashore. NPS / Dan Russell.

The National Park Service's San Francisco Bay Area Inventory and Monitoring Network, with Marin County Parks staff and volunteers, counts harbor seals at sites across Marin County, including Point Reyes National Seashore and Golden Gate National Recreation Area. In 2024, both of its counts hit record lows.

Breeding season: fewest pups on record

Over the 24 years the National Park Service has monitored harbor seals in Marin County, pup counts have been fairly stable, with occasional dips in El Niño years. In 2024, monitors counted 682 pups — the lowest ever recorded, well below the long-term average of 1,052. Lower counts in the previous few years had hinted a decline was beginning.

• Largest declines: Drakes Estero, Double Point and Tomales Point.
• Near or slightly below average: Tomales Bay, Bolinas Lagoon, Duxbury Reef and Point Bonita.

Why? Many factors affect pup production, so the cause is hard to pin down. Possible contributors:

• El Niño. The strong El Niño of 2023 and 2024 brought warm water, which can reduce harbor seals' prey and push it farther offshore, making foraging harder.
• Coyotes. More coyotes at Drakes Estero and Double Point in recent years may be driving seals to places that aren't surveyed, and monitors have seen coyotes kill pups.

Molt season: a long slide continues

Each summer, harbor seals of all ages except pups haul out on shore to molt — shed their fur and grow a new coat. Molt-season counts have been falling since at least 2021, and 2024 was the lowest on record: 1,788 seals, about half the long-term average of 3,366.

• Tomales Bay, Point Bonita and Bolinas Lagoon were about average or only slightly below.
• Drakes Estero, Double Point, Tomales Point and Duxbury Reef saw large declines. At Double Point and Drakes Estero — once the park's largest harbor seal sites in Marin — counts were down about 80% and 60% from their long-term averages; Double Point's molt counts began plunging in 2016, and Drakes Estero has had record lows for three years running.

Why molt-season numbers have fallen much further than breeding-season numbers, and why the decline has lasted so long, remain a mystery.

Data

The network publishes its pinniped monitoring data (1997–2023) as a data package on the NPS DataStore.

Sources

• National Park Service, San Francisco Bay Area Inventory and Monitoring Network: "2024 Harbor Seal Monitoring Updates."
• The source's charts of counts by site and year are not reproduced here, in keeping with the park's request that its monitoring graphics not be republished before official reports.