2017 Harbor Seal Monitoring Update

Unfortunately, this year, we were unable to survey Double Point due to safety concerns at the observation location. Double Point counts were removed from previous data in order to make appropriate comparisons to this year.

The peak pup count for the 2017 breeding season was approximately 745 pups, which is similar to the 17-year average. There was also very low pup mortality recorded at all sites. The sites with the largest pup counts were Drakes Estero (317) and Bolinas Lagoon (254). Bolinas Lagoon continues to increase in pups, with this being the highest count ever recorded at this site.

Ten harbor seals lying on a submerged sandbar
Harbor seals hauled out on a submerged sandbar in Bolinas Lagoon.

© Carlos Porrata

Following the breeding season, harbor seals of all age classes and sexes haul out on a daily basis to molt. The molt process consists of seals shedding their old fur and growing a new layer. The maximum molt count of all sites combined was approximately 2,630 seals, which is similar to the 17-year average. Although, a closer look at the individual sites shows that most sites had peak counts that were less than their respective averages, except for Bolinas Lagoon and Point Bonita. Bolinas Lagoon had a maximum count of 770 seals, which is much higher than the average count of 490 seals. The trend of increasing molt counts at this site has been seen since 2014 and the counts for both the 2017 and 2015 seasons are the highest counts ever recorded at Bolinas Lagoon.

Preliminary Data

Maximum Harbor Seal Count By Site

Maximum harbor seal counts by site, where Drakes Estero has the highest number of breeding adults, pups, and molting seals
Maximum harbor seal counts by survey site.

Total Weekly Maximum Harbor Seal Counts

Total weekly maximum harbor seal counts, where the maximum count of adults peaks near 2,350 the week of July 2
Total weekly maximum harbor seal counts across all Marin County monitoring sites.

The Details: Weekly Maximum Harbor Seal Counts By Site

Graph of maximum harbor seal counts by site and survey week from late February through July
Maximum weekly harbor seal counts by site and survey week
The National Park Service shall not be held liable for improper or incorrect use of the data described and/or contained herein. These data and related graphics are not legal documents and are not intended to be used as such. The information contained in these data is dynamic and may change over time. The data are not better than the original sources from which they were derived. It is the responsibility of the data user to use the data appropriately and consistent within the limitations of geospatial data in general and these data in particular. The related graphics are intended to aid the data user in acquiring relevant data; it is not appropriate to use the related graphics as data. The National Park Service gives no warranty, expressed or implied, as to the accuracy, reliability, or completeness of these data. It is strongly recommended that these data are directly acquired from an NPS server and not indirectly through other sources which may have changed the data in some way. Although these data have been processed successfully on computer systems at the National Park Service, no warranty expressed or implied is made regarding the utility of the data on other systems for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. The National Park Service requests that the data user refrain from publishing these data and related graphics and wait until data is available in official, published reports.

Last updated: December 22, 2017