Article

2025 Breeding Harbor Seal Monitoring Updates

By Marine Ecologist Sarah Codde, San Francisco Bay Area Inventory & Monitoring Network

Mother and pup harbor seals nose to nose as they rest with their hind ends in the water on a large, algae-covered rock.
A harbor seal mom embraces her pup by nudging their noses together.

NPS / Dan Russell

Simplified map of Marin County, CA, with seven, labeled dots indicating harbor seal breeding/monitoring locations. From North to South, they are Tomales Point, Tomales Bay, Drakes Estero, Double Point, Bolinas Lagoon, Duxbury Reef, and Point Bonita.
Harbor seal pupping sites in Point Reyes (light blue) and Golden Gate (dark blue).

Every spring, harbor seals gather in large groups throughout Marin County, CA, for the breeding season. During this time, a female harbor seal gives birth to a single pup. We see the highest number of pups around the end of April. In 2025, we counted approximately 853 pups at sites in Point Reyes National Seashore and Golden Gate National Recreation Area. This count is below the long-term average, but higher than in 2024, which was the lowest count on record during the 26-year monitoring period. This year's count is similar to counts recorded from 2021 through 2023. These were all lower than average, but within one standard deviation of the mean, which can represent natural variation in the counts.

Double Point, Drakes Estero, and Tomales Point all had pup counts that were below their respective long-term averages, while Bolinas Lagoon and Duxbury Reef had counts that were above average. The remaining sites, Tomales Bay and Point Bonita, had counts that were similar to their respective long-term averages. We continue to see the ongoing presence of coyotes at Drakes Estero and Double Point, which is possibly leading to the large decline at those sites. While Drakes Estero has experienced a decline in the number of pups born at that site in recent years, it is still the largest site in Marin County with approximately 236 pups recorded this year. Bolinas Lagoon is a close second with about 211 pups recorded this year.

Preliminary Data

2025 Maximum Harbor Seal Count By Site

Bar graph of maximum harbor seal counts at Tomales Point, Tomales Bay, Drakes Estero, Double Point, Bolinas Lagoon, Duxbury, and Point Bonita. Drakes Estero has the highest breeding season adult and pup numbers, followed by Bolinas Lagoon.
Maximum harbor seal counts by site during the breeding season (adults and pups).

Maximum Harbor Seal Pup Counts, 2000-2025

Line graph showing maximum harbor seal pup counts have remained fairly steady around the mean. The lowest count was recorded in 2024 and was far below the mean, but this year's count is back up near one standard deviation below the mean. 
Maximum harbor seal pup counts for 2000-2025 at Marin County sites. The black solid line on the graph represents the mean, or average, of the maximum pup counts from 2000-2024 (mean = 1,037), and the dashed lines represent one standard deviation from the mean. Not all sites were surveyed in 2020.

Maximum Harbor Seal Pup Counts by Site, 2000-2025

Line graph of harbor seal pup counts at 7 sites. Pt. Bonita and Duxbury Reef have the lowest, most consistent counts. Drakes Estero and Bolinas Lagoon have the highest, rebounding somewhat from lows last year.
Maximum harbor seal pup counts for 2000-2025 at Point Bonita, Bolinas Lagoon, Duxbury Reef, Double Point, Drakes Estero, Tomales Bay, and Tomales Point. Drakes Estero and Bolinas Lagoon counts rebounded most from last year's lows. Tomales Bay and Tomales Point sites also increased from 2024, while the other sites remained fairly stable. Not all sites were surveyed in 2020.

The Details: 2025 Weekly Maximum Breeding Season Harbor Seal Counts By Site

Graph of maximum harbor seal counts by site (Tomales Point, Tomales Bay, Drakes Estero, Double Point) and survey week from late February through May.
Graph of maximum harbor seal counts by site (Bolinas Lagoon, Duxbury Reef, Point Bonita) and survey week from late February through May.
Maximum weekly harbor seal counts by site and survey week.

For More Information

Logo text reads "SF Bay Area Inventory & Monitoring". Circular illustration of a scene combining distinctive rock formations, a redwood tree, and the Golden Gate Bridge over the SF Bay, each outlined in white. Illustrated binoculars overlap the scene.

Webpages

San Francisco Bay Area Network - Pinniped Monitoring

Pacific Coast Science and Learning Center - Harbor Seals

Data

Pinniped Monitoring for the San Francisco Bay Area Network: 1983-2024 - Data Package

Contact

Sarah Codde

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Last updated: July 15, 2025