Recovering Whales to Save Seabirds?

Recovery of Gray Whales may Halt Seabird Declines in Puget Sound

Oct 6, 2009

As Gray Whales on the Eastern Pacific Coast recover, their feeding activities have been shown to have positive and previously unnoticed effects on threatened seabirds.

For a long while the whale has been the poster child of conservation. However, shifts in population numbers often have unexpected effects on the local animal community, reminding us the the whale is not just a pretty face, but part of a functioning ecosystem.

Numbers of Eastern Pacific Gray Whales have increased so much in recent years that they were recently removed from the protection under the U.S. Endangered Species Act. And it turns out that this population boom isn't only good news for the whales.

Recovering Gray Whales Feed in a Unique Way That Kicks off the Ocean Food Chain

All whales disturb fish and crustaceans at the surface allowing opportunistic seabirds to catch an easy snack, but Gray Whales go one further in providing supper for their avian friends. Gray Whales are unique in being solely benthic feeders, meaning they only eat on the sea floor. The whales turn on their sides to scoop up huge mouthfuls of sediment from the bottom and use their baleen plates to sieve out small crustaceans, such as ghost shrimp. As they suction feed they throw up mud plumes, which mix vital nutrients into the surrounding waters, kicking off the planktonic food chain, and bringing up bottom dwelling life for birds to pick off. They also alter the sea floor by leaving behind large pits.

Conservation of Gray Whales Increases the Health of Declining Seabirds, Such as Scoters

Research by Eric Anderson and James Lovvorn (of the University of Wyoming at the time) suggests that protection of the Gray Whale population may be important for marine life, conserving the ocean food chain and providing food for certain declining seabirds, such as Scoters.

Anderson and Lovvorn's study showed that these 'whale pits' play an important part in the local ecosystem of Puget Sound, a complex of inland marine waterways in the northwestern part of Washington, U.S. Each year Gray Whales make a ten thousand mile migration between calving grounds in Baja California and their summer feeding grounds in the Arctic. Every year some of them break off their northern migration to come into shallow waters of Puget Sound to feed.

As the whales feed they dislodge and expose previously inaccessible invertebrate fauna in the sediment. This in turn attracts a host of invertebrate scavengers which remain abundant in these areas for extended periods. This increases the richness of these excavations as feeding grounds for bottom feeding sea birds, such as scoters (migratory sea ducks, which dive for crustaceans and molluscs). These make heavy use of Puget Sound as a winter feeding ground and numbers have been in decline.

Anderson and Lovvorn noted that scoters increased in whale feeding areas shortly after Gray Whale arrival in March and that certain species lost condition when the areas they inhabited were not well utilised by whales. This suggests that recent increases in whale feeding activity in Puget Sound could enhance feeding opportunities for scoters and other declining benthic feeding birds during the critical spring period, when energy for both migration and reproduction is paramount.

E. M. Anderson & J. R. Lovvorn (2008) Gray Whales may increase feeding opportunities for avian benthivores, Marine Ecology Progress Series 360: 291–296.

The Seadoc Society Website, "Recovering Gray Whales Could Help Declining Marine Birds" (February 2008).

The copyright of the article Recovering Whales to Save Seabirds? in Marine Conservation is owned by Sophie Morgan. Permission to republish Recovering Whales to Save Seabirds? in print or online must be granted by the author in writing.