State of the North Sound and Straits: Marine Mammals and Birds

Lauren Mulroy is a graduate of Huxley College and served as a RE Sources intern. Robyn du Pré served as the North Sound Baykeeper and coordinated water programs at RE Sources for eight years. She currently teaches field-based environmental studies for the Audubon Expedition Institute.

Part Four

Editor’s Note: This is the fourth of a multi-part series on the health of northern Puget Sound and Georgia Strait. It was first published under the title, “State of the North Sound and Straits,” by RE Sources and North Sound Baykeeper in October of 2002.

Nine mammalian species are commonly found throughout the sheltered inland waters of the North Puget Sound and Strait of Georgia, along with some occasional visitors. (Shepard)

Of the cetaceans in Puget Sound, orcas are the most well-known. Both resident and transient populations can be found in area waters. Transient orcas feed predominantly on harbor seals and other large marine animals, while the diet of resident orcas consists primarily of salmon.

Being top-level predators, orcas bioaccumulate fat-soluble toxins in their bodies. Blubber taken from orcas off the coasts of Washington and British Columbia was found to have very high concentrations of PCBs. Orcas are among the most contaminated marine mammals in the world.

This poses a serious threat when food supply is limited and orcas are required to utilize their fat reserves (Blue Voice, 2002). PCBs, and other fat-soluble toxins can weaken the immune system, cause skin diseases, reproductive failure, liver damage, nervous system disorders and cancer.

Orca populations are once again in serious decline. Between 1995 and 2000, the number of resident orcas of the inland marine waters of Washington and British Columbia dropped from 98 to 78 individuals. Scientists suggest a combination of factors have led to this precipitous decline, including dwindling salmon stocks, heavy boat traffic and toxic contamination. (Shepard)

A petition for listing the South Puget Sound resident orca population under the Endangered Species Act was submitted to the National Marine Fisheries Service (NMFS), but was denied in July 2002. NMFS contended that it is an “insignificant” population and is instead considering listing the population as “depleted” under the Marine Mammal Protection Act (MMPA). This would provide less protection than a listing under the ESA. (Environmental News Service, 2002)

Dwarfing the orca, gray whales are the largest visitors to the region. They feed on bottom-dwelling crustaceans, small schooling fish and ghost shrimp. Once hunted to near extinction, the gray whale population has rebounded, and evidence suggests there is now a summer resident population in Washington waters that forego the migration to the Bering Sea (CMC, 1998).

Gray whales visit Chuckanut Bay, and have been sighted in Bellingham Bay in recent years (Anchor, 2000). The gray whales’ presence can be linked to the health of the marine habitat that produces their prey.

Gray whales feed by diving to the ocean bottom and scooping up large amounts of sediments and bottom-dwelling organisms into their mouths. They then filter out the sediment through baleen (screen-like plates on the side of the mouth) while keeping the crustaceans and fish inside.

This feeding style lessens competition with other whales but puts gray whale populations in jeopardy if the sediment is contaminated. A decline in ghost shrimp or destruction of their sand-flat habitat could also pose serious threats for gray whales. Other threats include net entanglements, boat collisions, orca attacks and starvation.

Minkes are the smallest and most numerous baleen whales in the world. At least twenty individuals have been counted in the region during all months of the year, pointing to the possibility of a resident population. They primarily feed on squid, herring and other small fish that they filter out of the water column through their baleen.

Because Pacific herring are a primary food source, the decline of herring populations and of the eelgrass upon which herring spawn, are a threat to the minke population. Currently, minkes are not listed under the ESA, but are classified as protected under the Marine Mammal Protection Act. The small population in area waters appears healthy and stable.

Dall’s porpoises are the fastest cetaceans in the inland waters, being clocked at up to 30 knots (Osborne, 1988). They are present year-round and breed in local waters. Harbor porpoises are also year-round breeding residents of inland Washington and British Columbia waters (Marine Ecosystem Health Program [MEHP], 2002). Both porpoises have a similar diet of squid, shrimp, and small schooling fish. Harbor porpoises were once considered common, but now are rarely seen.

The decline in harbor porpoise populations makes them a candidate for an ESA listing in Washington State (MEHP, 2002). More research is needed to pinpoint causes for their population decline, but they are generally boat-shy and, therefore difficult to study. Entanglement in fishing nets is the most significant known threat to Dall’s and harbor porpoises. In addition, increased ship traffic drives harbor porpoises out of our waters (Osborne, 1988).

Year-round resident harbor seals make up the largest population of marine mammals in the Northwest Straits. They have made an impressive comeback from their decimated numbers prior to implementation of the Marine Mammal Protection Act in 1977.

A 1999 census indicated that approximately 14,600 harbor seals lived in Puget Sound and the Strait of Juan de Fuca. There has been an apparent slowing of harbor seal population growth in the Sound (PSWQAT, 2000). This slowing of population growth suggests the harbor seal population may have reached the limits that can be supported by the ecosystem.

Because they are higher-level predators, there are concerns about bioaccumulation of toxics in seals. A recent study compared the levels of Persistent Organic Pollutants in harbor seals throughout the Puget Sound and Northwest Straits. It shows that harbor seals in southern Puget Sound have higher levels of Polychlorinated Biphenyls (PCBs) than those of the Strait of Georgia.

Conversely, the harbor seals in the Strait of Georgia showed higher levels of dioxins and furans, both of which are by-products from pulp and paper mills in British Columbia (Transboundary GB-PSEIWG, 2002). Further research is needed to determine the effects of these pollutants on seal populations.

North Puget Sound and the Strait of Georgia are at the northern range of California sea lion habitat. In the past twenty years, they have become more abundant and can be seen in winter months hauled out on rock ledges in the region. This might be due to warmer ocean temperatures and a northern migration of some of their prey.

California sea lions feed primarily on hake and herring. California sea lions are classified as wildlife of state significance. Little research has been done to assess their population status in regional waters.

Stellar (or northern) sea lions are similar in appearance and behavior to the California sea lion. Their diet consists of squid, octopus, cod, rockfish and other fish. Due to declining population levels, Stellar sea lions have been listed as threatened under the Endangered Species Act.

The population in British Columbia waters is low, but stable. The most immediate threat to sea lions is entanglement in fishing nets and injury while eating fish off of long lines. While salmon make up just ten percent of their diet, some fishermen still consider sea lions a problem and kill them illegally (CMC, 1998).

River otters are the only Mustelids found in area waters, with the rare exception of a visit from the ocean-dwelling sea otter. River otters depend on healthy intertidal and coastal habitats for the many small crustaceans and other invertebrates upon which they feed. They also eat amphibians, fish and birds.

Little research has been done on river otters in Washington, but declines in the closely related European river otter populations have sparked some concern. Habitat loss, decreased water quality, and increased pollution are potential threats to otters (MEHP, 2002). River otters are included on the “watch list” in British Columbia, but have no listing status in the United States.

Serious Trouble: The drastic decline in our resident orca population points to alarmingly high levels of toxic contamination in the waters of north Puget Sound and the NW Straits. Declining populations and bioaccumulation of toxic substances in the fat of many other marine mammals point to an ecosystem-wide problem. However, rebounding populations of harbor seals and gray whales show us that these species can come back, even after serious population declines.

The health and abundance of seabirds, shorebirds and waterfowl are key indicators of health in the north Puget Sound marine ecosystem. Changes in critical habitat, entanglements in fishnets and human disturbances have all led to the decline of marine birds in the area. Of the 116 species of marine birds that utilize area waters, some populations appear relatively stable. Several species, however, are in danger.

Scoters are a common visitor to the area and represent the largest diving duck population in Puget Sound. Various species can be found in the winter months on the saltwater around Point Roberts, Birch, Lummi and Bellingham Bays, the outside of Semiahmoo Spit, Drayton Harbor, at Point Whitehorn and along the eastern shoreline of Georgia Strait, where they forage on herring spawn in the spring (Wahl, 1995).

In Skagit County, they can be found off of March Point at Fidalgo Bay, Washington Park in Anacortes and Rosario Head at Deception Pass (Skagit Audubon 2002). Department of Fish and Wildlife scientists have concluded that overwintering scoter numbers in greater Puget Sound have declined by 57 percent over the last 20 years (Getchell, 2002). During that same period, populations of 13 out of 18 other marine diving bird species in Puget Sound and the Northwest Straits declined as well.

Western grebe populations appear to have fallen even more precipitously over the last 20 years, showing an alarming 95 percent decline. Large flocks winter on Bellingham Bay and Boundary Bay, and smaller numbers winter in Drayton Harbor, Birch Bay, Lummi Bay and Chuckanut Bay (Wahl, 1995).

In 1978-79, 38,000 western grebes were present in greater Bellingham Bay (Wahl et al, 1981). Yet between 1993 and 1999, the Puget Sound Ambient Monitoring Program (PSAMP) conducted aerial surveys and never recorded more than 5,700 birds in that area. While we do not have such detailed data for Skagit County, this trend appears to hold throughout the Puget Sound region.

Other declines in area marine bird populations include scaup—down by 72 percent, long-tailed ducks—down by 91 percent, and marbled murrelets—down by 96 percent. In contrast, harlequin duck populations are up by 190 percent (Getchell, 2002).

A variety of human activities have led to the decline in numbers of many marine birds. Habitat loss and shootings have both contributed to the decline of western grebe and scoter populations. Oil spills and reductions in prey base have detrimental effects on various species of seabirds and waterfowl.

A surprising number of birds are killed each year via entanglements in fishing nets. Diving birds, such as the threatened murrelet, are especially prone to entanglement and drowning in fishnets. In 1994, the Washington State Department of Fish and Wildlife estimated that 3,569 seabirds were caught in commercial fishing nets, with 90 percent taken around the San Juan Islands (WDFW, 2002).

Habitat disturbance is a major threat to marine birds and waterfowl. Changes in habitats occur because of physical alterations to the land, various types of pollutants, and from increasing human activities, such as recreational and commercial vessel traffic.

Recreational boaters can be a particular problem as growing numbers of Washingtonians take to the water each year. Certainly, motorized vessels such as motorboats and jet-skis, are great disturbances to waterfowl. But even kayakers who paddle too close to resting and nesting flocks can pose a disturbance. (Wahl, 2002)

Dwindling numbers of forage fish at many over-wintering sites might be a contributing factor to the decrease in marine bird populations. Bird species that either eat fish or depend upon specific spawning events of Puget Sound forage fish appear to have declined more than bird species that have a more generalized diet.

Serious Trouble: In general, marine bird populations are declining, some precipitously. Destruction of habitat, reductions in food sources, entanglement in fishing gear, and disturbances by boaters all contribute to the continued decline of marine bird populations in area waters. §

Next Month—Part Five