Marine Mammals in the Southwestern Strait of Juan de Fuca: Natural History and Potential Impacts of Harbor Development in Neah Bay

A one year study of marine mammals between Tatoosh Island and Pillar Point on the southwestern portion of the Strait of Juan de Fuca was conducted by Cascadia Research under contract to the Army Corps of Engineers. The goal of the project was to determine the occurrence of marine mammals in the area and evaluate the potential impacts on marine mammals of construction and operation of a log export facility, deepwater channel, and small boat harbor in Neah Bay. 

Monthly aerial, land, and boat surveys were conducted between August 1985 and July 1986. Boat surveys covered a total of 1,825 nautical miles (nm) and aerial surveys 1,135 nm. Both aerial and boat surveys had three components: 1) shoreline surveys for pinnipeds hauled out and other marine mammals near the shore, 2) transects 1 nm offshore that paralleled the shoreline, and 3) offshore transects running perpendicular to the shore extending out 3 nm. Land observations were conducted from several locations primarily to count pinnipeds at haul-out areas, monitor the northbound gray whale migration, and make observations of marine mammals at the entrance and in Neah Bay. Residents of the study area were questioned about marine mammal occurrence in previous years and recruited to record marine mammal sightings. 

Additional study effort was focused on the gray whale because of its status as an endangered species. Research efforts included monitoring the gray whale migration, photographically identifying and tracking individual non-migrating animals, measuring the lengths (and hence age class) of gray whales residing in the study area, and examining aspects of gray whale behavior. 

Just under 800 sightings of 10 marine mammal species (including river otter) were made in the study area, primarily from boat surveys. Harbor seals were the most commonly seen marine mammals and occurred year-round in the study area. Harbor seals hauled out at 19 locations in the study area, with highest concentrations at Tatoosh Island and between Slip and Pillar Points. California sea lions were the next most abundant species and were present from September to June with highest numbers from December to May. They were most common in Neah Bay where up to 30 congregated in the water to feed on discarded fish remains. the sea lions first occurred in numbers the previous year. Large numbers of California sea lions migrate through the study area and pass the entrance to Neah Bay from March to June. Northern sea lions were seen in highest numbers at Tatoosh Island, where they were seen hauled out in the summer and fall. Northern sea lion abundance was lowest in summer. Migrating northern sea lions were seen following the same route and timing in the study area as California sea lions, but in smaller numbers. A single northern elephant seal was seen in the study area. Elephant seals have been reported as occasional visitors to the study area with most sightings at Tatoosh Island or offshore. 

River otters and a single sea otter were seen in the study area and most often near the entrance to Neah Bay. River otters were seen during all seasons, with up to seven river otters seen at one time at the entrance to Neah Bay. A single sea otter was seen on six occasions between 18 and 24 November 1985 just outside Neah Bay off First Beach. It is one of the few confirmed sightings in recent years of a sea otter in inland waters of Washington State. 

Two species of small cetaceans were frequently seen in the study area. Harbor porpoise were the most abundant cetacean and were seen primarily from 0.5 to 1.5 nm offshore. Sighting frequency of harbor porpoise varied by region with greatest numbers seen off the Sekiu River and Kydaka Point. Harbor porpoise were present in all seasons but were most numerous in fall. Dall’s porpoise were seen less often than harbor porpoise and tended to occur farther offshore. Dall’s porpoise were seen in all seasons. 

Three other species of cetaceans were seen or reported in the study area. Both killer whales and minke whales are occasional visitors to the study area. The gray whale migrates past Cape Flattery and Tatoosh Island at the western edge of the study area. During the southbound migration in December and January, few gray whales entered the study area. The highest number of animals migrating north was seen in early March, earlier than expected. Gray whales migrating north generally passed on the west side of Tatoosh Island. 

Some gray whales reside in the study area for prolonged periods. Seven gray whales seen in the study area were individually identified through photographs. These seven animals accounted for 55 of the 68 sightings of gray whales in the study area. Gray whales in the study area were observed foraging on numerous occasions and spend an estimated 44% of the time foraging. Most foraging locations were between Waadah Island (Neah Bay) and the Sekiu River. One whale stayed in the study area at least from January to late April and apparently never migrated to the breeding lagoons in Mexico. One identified gray whale was seen on the last survey on 15 July 1986. Residents reported one whale stayed until late September 1986. Six gray whales (including three of the individually identified whales) were measured through aerial photogrammetry in or adjacent to the study area. Five of these six were between 7.1 and 7.8 m in length and were judged to be yearlings; the sixth animal was 9.3 m long. Gray whales frequently entered Neah Bay or passed across the entrance to Neah Bay. One identified gray whale died, apparently from entanglement in a gillnet, and reports from people in the area indicated this was not uncommon. 

Shock waves from blasting, required for constructing a deep water channel, could potentially impact marine mammals in the study area. California sea lions are considered the most likely species to be impacted by blasting because of the large number that congregate in Neah Bay. Gray whales, harbor seals, river otters, northern sea lions, and sea otters all occasionally occurred in the area where blasting would occur. All other species were considered to be rare visitors to the Neah Bay area and therefore likely outside the impact range of the blast shock waves. Methods are available to both reduce the force of the shock waves and reduce the chances of marine mammals occurring in the study area at the time of blasting. Potential long-term impacts on marine mammals of operation of a log export facility and small boat harbor include: 1) disturbance from increased boat and vessel traffic, 2) degradation of water quality, and 3) decreased prey availability. These potential long-term effects of Neah Bay development appear unlikely to occur at a level detrimental to marine mammals in the vicinity. The most important problems are potential blast-related impacts on California sea lions, that are abundant in Neah Bay, and gray whales, which are classified as endangered by the state and the federal government. Some additional research is recommended on these two species. 


Calambokidis, J., G.H. Steiger, and J.C. Cubbage. 1987. Marine Mammals in the Southwestern Strait of Juan de Fuca: Natural History and Potential Impacts of Harbor Development in Neah Bay. Final report for Contract No. DACW67-85-M-0046 from Corps of Engineers, Seattle, Washington. 103pp.

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