Introduction & Objectives

Guadalupe fur seals are listed as threatened under the U.S. Endangered Species Act and endangered under Mexican law. However, prior to the first year of this study in 2018, the last full census for this species was in 2010, making it difficult to develop current and accurate population estimates and trends. To determine the degree to which this recovering population uses U.S. Navy training and testing ranges in the North Pacific, updated population information for Guadalupe fur seals is needed in addition to tracking at-sea movement patterns using satellite transmitters. 

There are two principle components of this multiyear study: (1) updating overall population information for Guadalupe fur seals, and (2) tracking the at-sea movement patterns of this species using satellite transmitters.

Technical Approach

Guadalupe fur seal population monitoring surveys were conducted at Guadalupe Island, México, and San Benito Archipelago, México, during the 2019 summer breeding season (June-August) because this is when the most animals are found on land.

Direct counts of Guadalupe fur seals were conducted at San Benito Archipelago using the same methodologies as those used in previous years. Briefly, for the three islands in this archipelago, land-based surveys (walked inland of the animals) were used for all areas of the coastline accessible by foot. Surveys from a small boat

A remotely piloted aircraft (RPA or drone) was also utilized to test the feasibility of aerial imagery to improve counts at Punta Sur to replace or supplement walk-through surveys because these create disturbance for mothers with

Progress & Results

At San Benito Archipelago, twice as many Guadalupe fur seals were counted in 2019 relative to 2018.  In 2019, 90% of the fur seal were juveniles, compared with 84% in 2018, but similar to every other survey at this site since fur seals were rediscovered here in 1997, less than 30 mom-pup pairs were observed. Therefore, San Benito Archipelago still is considered a recolonization site rather than an established rookery. Guadalupe Island remains the only established rookery (breeding site) for the Guadalupe fur seal population.

Emigration of animals from Guadalupe Island to San Benito Archipelago that occurred during the first phase of recolonization may still occur with juveniles displaced to San Benito Archipelago from Guadalupe Island during the breeding season. However, no movements between these two sites were recorded for juvenile fur seals captured at Guadalupe Island and tracked using satellite telemetry instruments through the breeding season, and the exchange of Guadalupe fur seals between these two sites remains unknown. Continued population monitoring is necessary to better understand the relationship between Guadalupe fur seal abundance at these two sites.

In terms of overall abundance, fur seal population estimates frequently are extrapolated from pup counts. Increased pup mortality in 2014-2015 could lead to an approximately 5-year delay in decreased recruitment of breeding females and a corresponding decrease in the number of pups born in 2019. Although there were no pup counts from 2014-2017, from 2018 to 2019, pup counts decreased by 19.2% at Guadalupe Island. This decrease from one year to the next may reflect interannual fluctuations or a longer term decrease in abundance, and ongoing annual censuses are needed to tease apart the drivers of these population trends.