Pacific white-sided dolphins in the Salish Sea

Pacific white-sided dolphins (Lagenorhynchus obliquidens) are found in the colder offshore waters of the North Pacific, but they also occasionally occur in inshore waters of the Salish Sea, and more rarely, Puget Sound. They make use of cooperative foraging techniques, and feeding at night in dark conditions means their finely tuned sonar or echolocation serves them well.

A pair of dolphins leaping out of water side by side.
Two Pacific white-sided dolphins from a large school of several hundred jump in the wake of a research vessel off the coast of Washington, showing their lovely color patterns. Photo: Thomas A. Jefferson (taken under NMFS Permit #22306).

Overview

Pacific white-sided dolphins (commonly known as “lags” among marine mammal enthusiasts) are endemic to the North Pacific Ocean and adjacent waters. These graceful and beautifully-marked dolphins are well known to mariners in the colder offshore waters of the North Pacific, but they also occasionally occur in inshore waters of the Salish Sea – the Strait of Juan de Fuca, Georgia Strait, and more rarely, Puget Sound. The large schools that characterize them in offshore areas are not common in the Salish Sea, where they usually occur only in small groups. However, when they do show up, their handsome color patterns and spectacular behavior make them a welcome sight. The scientific name of the Pacific white-sided dolphin, Lagenorhynchus obliquidens, was given by Theodore Gill in 1865, when he described the species for the first time. The genus name refers to the bottle- or flask-shaped beak, and the species epithet refers to the obliquely-angled teeth.

Status, trends & events

Pacific white-sided dolphin numbers along the west coast of the US vary somewhat from year to year, but so far there has been no significant long-term trend identified (Carretta et al. 2023). In fact, the species distribution model suggests a very stable population from 1996-2018.

The animals that occur in the US portion of the Salish Sea are members of the California/Oregon/Washington stocks of Pacific white-sided dolphins, which were estimated to contain a total of 34,999 (CV=0.22) individuals in 2018 (Carretta et al. 2023). The two stocks (a northern and a southern one) are currently not able to be reliably distinguished based on external appearance. The number of animals in US waters fluctuates with varying ocean conditions, but so far there have been no trends identified in their numbers (Carretta et al. 2023).

Pacific white-sided dolphins are not considered to be an endangered species and are not listed as Threatened or Endangered under the US Endangered Species Act. While fisheries by-catch does occur in both the US and Canada, these animals have never been exploited in significant numbers along our coast, and therefore the populations are generally considered healthy.

 

A single dolphin leaping above water.
A Pacific white-sided dolphin porpoises out of the water as it moves along with a fast-moving school that included a smattering of northern right whale dolphins as well. These two species are frequent associates off the west coast of the US. Photo by the author (photo taken under NMFS Permit #22306).

Natural history

 

Map showing the global distrubtion of Pacific white-sided dolphins
Pacific white-sided dolphin global range (map by Nina Lisowski, from Jefferson et al. 2015).

The Pacific white-sided dolphin occurs only in the North Pacific Ocean and adjacent seas, from the southern Gulf of California and central China to just north of the Aleutian Islands in the Bering Sea (Brownell et al. 1999). The dolphins are much more common and more abundant in the northern portions of their range than in the southern parts. They are a coldwater species, and their main habitat is offshore waters of the continental shelf and slope, although they do also occur in very deep oceanic waters. The Washington and British Columbia (BC) records suggest an inshore movement in winter and an offshore movement in summer (Pike & MacAskie 1969).

In Puget Sound and the Salish Sea, Pacific white-sided dolphins have traditionally been considered relatively uncommon (Everitt et al 1979; Angell and Balcomb 1982; Stacey and Baird 1991; Calambokidis and Baird 1994). The Strait of Juan de Fuca, which connects to the open sea is the place one is most likely to find them (Everitt et al 1979). The seasonality of their appearance in inshore waters has been somewhat controversial, but most reports mention fall as a peak season. Gaydos and Pearson (2011) considered their occupancy of the Salish Sea to be low in winter, spring, and fall, and rare in summer. Osborne et al. (1988) stated that lags are regular summer/fall visitors to the Strait of Juan de Fuca, around Race Rocks and off San Juan Island. When observed further south into Puget Sound proper, it is usually just singles or pairs that are seen, with dolphins sometimes stranding. There are indeed stranding records in Puget Sound, with some as far south as the area between Olympia and Tacoma, though these appear to be uncommon (Norman et al. 2004). Shuster et al. (2018) stated that lags were the only species of dolphin commonly found in the inshore waters of Washington State. However, in 35,102 km of aerial surveys for marine mammals, covering all four seasons, and the entire Puget Sound in 2013-2016, lags were not observed (Smultea et al. 2017), so their occurrence might be considered sporadic. Further north, in the inshore waters of British Columba, while previously considered rare, they have been sighted (and stranded) with increasing frequency in recent decades, and they are now frequent visitors to BC’s inshore channels and passes (Ford 2014).

Feeding

Feeding is mainly on small schooling fishes that occur in the upper and middle zones of the ocean, including lanternfish, anchovies, sauries, horse mackerel, and hake, as well as cephalopods (e.g., market squid). They almost certainly make use of cooperative foraging techniques and much of their feeding may be on deep scattering layer (DSL) organisms, which perform daily vertical migrations, reaching near-surface waters at night. Feeding mainly at night and in dark conditions means that the dolphins would not have to dive as deep to access prey, and their finely tuned sonar or echolocation would serve them well in these dark waters (Brownell et al. 1999; Heise 1997).

Biology

The Pacific white-sided dolphin is a medium-sized dolphin. Adults in the Eastern North Pacific reach about 2.5 m in length (males) and 2.4 m (females), and newborns are about 92–100 cm long. Maximum weight is about 198 kg. They are rather stocky, with a very short, but well-defined, beak. The color pattern has various shades of black, white, and gray, but is complex. It is dark gray on the back and white on the belly, with a large thoracic patch of light gray on the side. The sides and belly are separated by a distinct black line, and the dorsal fin is bicolored (dark on the leading half and white on the latter). Several anomalous color patterns have been observed, including melanistic and leucistic ones, but the most frequent of these has a very dark thoracic patch surrounded by a distinct and wide white border. This latter form is called the “Brownell-type.”

These dolphins often occur in large schools of hundreds or even thousands in offshore waters, but inshore they are usually encountered in much smaller groups of just a few dozen or even less. They are often seen porpoising out of the water, rising up and down in unison, as they move rapidly along the surface in broad ranks. Aerial behavior (e.g., breaches, flips, flipper and fluke slaps, etc.) is frequent, and these dolphins are avid bow riders, preferring to ride on ships moving at moderate speeds. Bow riding may have been an adaptation of their “snout riding’ behavior on the pressure waves pushed forward by the heads of large whales, such as blue and fin whales.

Like most other species of dolphins, Pacific white-sided dolphins produce a wide variety of whistles, clicks, and burst-pulse sounds – they are a highly vocal species. The clicks are mainly used in echolocation to navigate, locate objects and other animals, and find prey. Whistles and burst-pulse calls (a variety of which have been called squeeks, squeals, and squawks) are likely used mainly in communication with members of the same species, and there is some evidence of the use of a signature whistle, such as those well known for bottlenose dolphins (Tursiops truncatus).

The main predator of the Pacific white-sided dolphin is Bigg’s killer whale (Orcinus orca rectipinnus). Although it appears that killer whales prefer other marine mammal prey (such as harbor porpoise, Dall’s porpoise, and pinnipeds), there are records of these predators attacking and killing dolphins of several species, including Pacific white-sided dolphins. Marks from presumed killer whale attacks are 8 times more common than marks from anthropogenic sources in the Broughton archipelago (north of the Salish Sea in BC waters), suggesting that killer whale predation is a major factor in lag population status there (Ashe 2015; Ashe et al. 2021). Sharks may occasionally attack them as well, but they do not appear to be important predators. Beside predatory interactions, these dolphins also occur in mixed groups with other species of marine mammals, most commonly northern right whale dolphins (Lissodelphis borealis), and Risso’s dolphins (Grampus griseus).

Human impacts on Pacific white-sided dolphins appear to be less severe than they are for many other species of marine mammals. They have never been hunted in significant numbers along our coasts, though they are sometimes taken in drive fisheries in Japan. Pike (1960) mentions some taken by hand harpoon in the Strait of Juan de Fuca but does not say when or why the animals were taken (for research, sport, or food?). He was probably referring to a dolphin mentioned by Scheffer and Slipp (1948), which was harpooned from the oceanographic research vessel Catalyst in 1936. The main impact from humans these days is probably from by-catch in various gillnet and driftnet fisheries in both the US and Canada, but at present these takes do not appear to be endangering populations. Climate change is undoubtedly affecting the distribution of these animals, with their southern limits being pushed to the north as waters warm, but there is little evidence that this is a serious threat to these animals at present.

There have been no dedicated studies on Pacific white-sided dolphins in the Salish Sea or Puget Sound waters, and most or all of what we know comes from opportunistic observations. However, further north in the Broughton archipelago, Pacific white-sided dolphins have been studied for several decades by Alex Morton, and more recently by Erin Ashe. Lag occurrence there increased from 1984-1998 and peaked in the months of October through January. Morton (2000) photo-identified 675 individuals, with 214 of them resighted, and this photo-ID work has been extended by the work of Ashe (Ashe 2015; Ashe et al. 2021). If these animals continue to be found in Salish Sea waters, perhaps some dedicated researchers will take up more directed studies on them and help resolve some of the uncertainties about these fascinating animals.

Data sources & gaps

Most status information in this report comes from Carretta et al. (2023). While some monitoring and information gaps for this species exist, there is generally adequate information to determine the status and trends of this species along the West Coast. Information specific to the Salish Sea or Puget Sound, however, is largely lacking.

Methods & statistics

Methods of determining the population status of the California/Oregon/Washington stock of Pacific white-sided dolphins mostly comes from vessel-based line-transect analysis, and habitat-based species distribution modeling (see Carretta et al., 2023).

References

Angell, T., & Balcomb, K. C. (1982). Marine Birds and Mammals of Puget Sound: Puget Sound Books.

Ashe, E. (2015). Ecology of Pacific White-Sided Dolphins (Lagenorhynchus obliquidens) in the Coastal Waters of British Columbia, Canada. (Ph.D. thesis). University of St Andrews, St Andrews, Scotland.

Ashe, E., Williams, R., Morton, A., & Hammond, P. S. (2021). Disentangling Natural and Anthropogenic Forms of Mortality and Serious Injury in a Poorly Studied Pelagic Dolphin. Frontiers in Marine Science, 8. doi:10.3389/fmars.2021.606876

Brownell, R. L., Walker, W. A., & Forney, K. A. (1999). Pacific white-sided dolphin Lagenorhynchus obliquidens Gill, 1865. In S. H. Ridgway & R. Harrison (Eds.), Handbook of Marine Mammals, Volume 6: The second book of dolphins and the porpoises (pp. 57-84): Academic Press.

Calambokidis, J., & Baird, R. W. (1994). Status of marine mammals in the Strait of Georgia, Puget Sound and the Juan de Fuca Strait and potential human impacts. In R. C. H. Wilson, R. J. Beamish, F. Aitkens, & J. Bell (Eds.), Review of the marine environment and biota of Strait of Georgia, Puget Sound and Juan de Fuca Strait (Vol. 1948, pp. 282-303): Canadian Technical Report of Fisheries and Aquatic Sciences.

Carretta, J. V., Oleson, E. M., Forney, K. A., Weller, D. W., Lang, A. R., Baker, J., . . . Brownell Jr., R. L. (2023). U.S. Pacific marine mammal stock assessments: 2022. NOAA Technical Memorandum NMFS-SWFSC, 684, 404 pp.

Everitt, R. D., Fiscus, C. H., & DeLong, R. L. (1979). Marine mammals of northern Puget Sound and the Straits of Juan de Fuca. NOAA Technical Memorandum ERL-MESA, 41, 141 pp.

Ford, J. K. B. (2014). Marine mammals of British Columbia. Royal British Columbia Museum, Victoria, British Columbia, Canada. 460 pp.

Gaydos, J. K., & Pearson, S. F. (2011). Birds and mammals that depend on the Salish Sea: A compilation. Northwestern Naturalist, 92, 79-94.

Heise, K. (1997). Diet and feeding behavior of Pacific white-sided dolphins (Lagenorhynchus obliquidens) as revealed through the collection of prey fragments and stomach content analysis. Reports of the International Whaling Commission, 47, 807-816.

Jefferson, T. A., Webber, M. A., & Pitman, R. L. (2015). Marine Mammals of the World: A Comprehensive Guide to Their Identification: Academic Press/Elsevier.

Morton, A. (2000). Occurrence, photo-identification and prey of Pacific white-sided dolphins (Lagenorhynchus obliquidens) in the Broughton Archipelago, Canada 1984-1998. Marine Mammal Science, 16(1), 80-93.

Norman, S. A., Bowlby, C. E., Brancato, M. S., Calambokidis, J., et al. (2004). Cetacean strandings in Oregon and Washington between 1930 and 2002. Journal of Cetacean Research and Management, 6(1), 87-100.

Osborne, R., Calambokidis, J., & Dorsey, E. (1988). A Guide to Marine Mammals of Greater Puget Sound: Island Publishers.

Pike, G. C. (1960). Pacific striped dolphin, Lagenorhynchus obliquidens, off the coast of British Columbia. Journal of the Fisheries Research Board of Canada, 17, 123-124.

Pike, G. C., & MacAskie, I. B. (1969). Marine mammals of British Columbia. Bulletin of the Fisheries Research Board of Canada, 171, 54 pp.

Scheffer, V. B., & Slipp, J. W. (1948). The whales and dolphins of Washington State, with a key to the cetaceans of the west coast of North America. American Midland Naturalist, 39, 257-337.

Shuster, L., & D. Anderson, J. L. H., A. B. Douglas, N. Harrison, J. Calambokidis & S. Berta. (2018). Dolphins in the Salish Sea: Are warmer water species expanding into our region? Unpublished conference presentation.

Smultea, M. A., K. Lomac‐MacNair, G. C., S. S. Courbis, & Jefferson, T. A. (2017). Aerial survey of marine mammals conducted in the inland Puget Sound waters of Washington, summer 2013–winter 2016. Final Report. Final report to the US Navy.

Stacey, P. J., & Baird, R. W. (1991). Status of the Pacific white-sided dolphin, Lagenorhynchus obliquidens, in Canada. Canadian Field-Naturalist, 105, 219-232.

Links

Caretta, James V, et al. DRAFT U.S. Pacific marine mammal stock assessments: 2023. NOAA Technical Memorandum NMFS-SWFSC-XXX. https://www.fisheries.noaa.gov/s3/2024-01/Draft-2023-Pacific-MMSARs.pdf

Puget Sound dolphin and porpoise species identification video. Cascadia Research Collective. https://cascadiaresearch.org/project_article/puget-sound-dolphin-and/

Pacific white-sided dolphins in Eastsound. SeaDoc Society. https://youtu.be/o6UM7eRnOFY?si=3d8UyVl4kN7x5Uj4

Acknowledgements

The author thanks the University of Washington Puget Sound Institute and the Environmental Protection Agency for funding this overview, and also the Puget Sound Ecosystem Monitoring Program's Marine Mammals Working Group for helping to facilitate the production of this chapter.

Licensing & attribution

Data and products from the PSEMP Marine Mammal Work Group are governed by a Creative Commons BY-NC-SA license. Attribution should be to: “PSEMP Marine Mammal Work Group” with a link back to https://psemp.net/mmwg.

About the Author: 
Thomas A. Jefferson is the director of Clymene Enterprises and is also an independent researcher at NOAA's Southwest Fisheries Science Center.