Introduction & Objectives

To meet information needs of the US Navy, Pacific Fleet Environmental, the National Marine Fisheries Service, Marine Mammal Laboratory in collaboration with Washington Department of Fish and Wildlife conducted a study of adult male California sea lions (Zalophus californianus) with two objectives: 1) to estimate the number of sea lions that use Navy Facilities in Puget Sound, Washington and 2) to describe how adult male sea lions utilize the waters of Washington as marine foraging areas.

Technical Approach

Weekly counts of sea lions were conducted at four Navy Facilities in Puget Sound, Washington (WA) to estimate abundance and satellite dive recorders were deployed on adult male California sea lions to obtain data on the proportion of time the animals were hauled out and their distribution and diving behavior as they foraged in inland and coastal waters.

To describe distribution, haul out and diving behavior, 30 adult male California sea lions were captured using a floating trap outside of Navy Base Kitsap-Bremerton and at Clam Bay near Manchester from 2014 to 2016. Captured animals were sedated or anesthetized and Satellite Dive Recorders (SDRs) were attached to their dorsal pelage using epoxy glue. The SDRs transmitted “dry time” haul out, location and diving data through the Argos System satellite network.

Progress & Results

Locations for 30 animals and haul out and diving for 26 animals over a two-year period were recorded. Instruments attached to animals transmitted data to the satellite for 8 to 184 days before the instruments were lost from the animals. A total of 59,645 hourly locations for 30 sea lions, and 234,034 dives and 12,786 hours of haul out behavior for 26 animals, represented 67 animal-months of behavior.

From the location data, it became apparent that most adult male sea lions were transient visitors to the Navy Facilities in Puget Sound. Ten of 30 animals remained in Puget Sound for up to four months following instrumentation. The majority of the instrumented animals left the vicinity of the Navy Facility where they were tagged within a month after instrumentation. Their movements were apparently determined by the presence of locally abundant prey.

Eleven animals that moved from Puget Sound to the Columbia River passed through the Olympic Coast National Marine Sanctuary (OCNMS) and some hauled out on traditional haul sites within the OCNMS. A total of 19 animals used the outer coast regions producing 7,398 hourly estimated locations. Of these locations, 79% occurred between the coast and the eastern edge of the Northwest Training and Testing Area (NWTTA) and 21% occurred within the NWTTA.

Researchers recorded 234,034 dives greater than 4 m by 26 animals in all geographic regions during this study. The majority of dives occurred in Washington Inland Waters. Most of the diving in the WA Inland Waters was less than 20 m, but some dives were greater than 250 m. Dives were mostly less than 4 min in duration but some longer dives were greater than 10 min.

Abundance at all of the facilities was highest in October and November, followed by March and April. Abundance was near zero in June and July. The highest abundance by facility occurred at Bremerton in November, Everett in October, Bangor in November, and Manchester in December. The estimate of abundance of sea lions using all four Navy Facilities in the inland waters of Washington was 788 (99% CI: 534-1186). The upper 99% confidence interval of 1186 animals provides a risk-averse estimate of the number of sea lions potentially affected by Navy activities at any of the Facilities in the inland waters of Washington.