Columbia River Estuary

The numbers of double-crested cormorants nesting in the Columbia River estuary have increased dramatically in the last two decades. During the period 1997-2010 the cormorant colony on East Sand Island increased 170% to ca. 13,600 breeding pairs, the largest known breeding colony for the species in western North America. Although juvenile salmonids represented only ca. 10% of the diet of cormorants nesting on East Sand Island in 1999-2010, estimated smolt consumption by the cormorant colony (19.2 million smolts; 95% c.i. = 14.6–23.8 million) is now greater than that of the Caspian tern colony on East Sand Island. The large numbers of smolts consumed by the East Sand Island cormorant colony are due to both the larger size of the cormorant colony and the greater food requirements of cormorants relative to Caspian terns. The double-crested cormorant colony on East Sand Island has experienced high nesting success in recent years (2.1 young raised/breeding pair in 2001-2010), perhaps contributing to the increase in colony size and its current and future impacts on smolt survival.

Resource management agencies have decided that management of the large colony of double-crested cormorants on East Sand Island in order to reduce losses of ESA-listed juvenile salmonids in the Columbia River estuary warrants consideration. Reduction in the size of the cormorant colony on East Sand Island is one management option under consideration. Feasibility studies to test techniques for dissuading double-crested cormorants from nesting on a portion of the East Sand Island colony have met with some success.