2022 Harbor Seal Monitoring Updates

Harbor seals live a dual life, spending half their time on land and the other half in the ocean. This duality means they have to avoid both terrestrial and oceanic predators. In recent years, the harbor seals in Marin County have been dealing with more interactions from coyotes. Biologists monitoring the seals in 2022 continued to see this issue.

Coyotes have become a more regular sighting at some of the harbor seal locations in recent years, but this is the first time in many years that we have seen one at Bolinas Lagoon.

Sue Van Der Wal / NPS Volunteer

In the spring months, National Park Service staff and volunteers from the Harbor Seal Monitoring Program monitor the seals during the breeding season. Then over the summer, we monitor them during their molt season—when the seals are onshore for extended amounts of time shedding their fur and growing a new layer. The first site where we began seeing coyotes more regularly was Double Point about five years ago. At the same time, we saw a decline in the number of seals hauling out at that location. Then in 2021, we saw multiple coyotes regularly at Drakes Estero and the number of seals there also dropped dramatically. Again, in 2022, we recorded low numbers of seals hauling out in Drakes Estero and Double Point.

Breeding Season Summary

The total number of pups recorded during the breeding season in Marin County this year was 876. While this is one of the lowest counts on record for the monitoring program, we normally see cycles of high and low counts during the breeding season. Our long-term data show that harbor seal reproductive success overall is fairly stable. The next few years will show us if the numbers bounce back up or if we see a continued decline. All monitoring locations had lower than average counts this year except Bolinas Lagoon—which has had higher than average counts for the past few years—and Point Bonita in the Marin Headlands, which is a small pupping site.

Molting Season Summary

The total number of seals recorded during the molt season in Marin County this year was 2,149. This is far below the long-term average of 3,490 seals and is the lowest count ever recorded for the monitoring program. This decline has been ongoing for many years. Drakes Estero and Double Point saw dramatically low counts with this year's counts being more than 50% below their respective long-term averages. Bolinas Lagoon was the only site to have a higher-than-average count during the molt season. This location has become a very important site for Marin's harbor seals. Unfortunately, a coyote was seen at this harbor seal colony at the end of the molt season, and it killed a seal. We will have to see next year if coyotes become a regular occurrence at the Bolinas Lagoon harbor seal sites and affect how the seals use that area.

A special thank you to the Marin County Parks Natural Resources staff for assisting with harbor seal monitoring at Bolinas Lagoon this year. We hope this becomes a permanent collaboration between the two agencies.

Preliminary Data

2022 Maximum Harbor Seal Count By Site

Maximum harbor seal counts by site during the breeding season (adults and pups) and molt season (all seals).

Maximum Harbor Seal Pup Counts, 2000-2022

Maximum harbor seal pup counts for 2000-2022 at Marin County sites. The black solid line on the graph represents the mean, or average, of the maximum pup counts from 2000-2021 (mean = 1,069), and the dashed lines represent one standard deviation from the mean. Not all sites were surveyed in 2020.

Maximum Harbor Seal Molt Counts, 2000-2022

Maximum harbor seal molt season counts for 2000-2022 at Marin County sites. The black solid line on the graph represents the mean, or average, of the maximum seal counts from 2000-2021 (mean = 3,490). Dashed lines represent one standard deviation from the mean. Not all sites were surveyed in 2020.

The Details: 2022 Weekly Maximum Harbor Seal Counts By Site

Maximum weekly harbor seal counts by site and survey week.

For More Information

Contact

Sarah Codde

Webpages

San Francisco Bay Area Network - Pinniped Monitoring

Pacific Coast Science and Learning Center - Harbor Seals

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