Caspian Tern Management Plan

In 2008, the U.S. Army Corps of Engineers (USACE) began implementing the Caspian tern management actions outlined in the January 2005 Final Environmental Impact Statement (FEIS) and November 2006 Records of Decision (RODs) for Caspian Tern Management to Reduce Predation of Juvenile Salmonids in the Columbia River Estuary. This management plan, which was developed jointly by the USACE, the U.S. Fish and Wildlife Service, and NOAA Fisheries, seeks to redistribute a portion of the Caspian tern colony on East Sand Island in the Columbia River estuary to alternative colony sites in interior Oregon and the San Francisco Bay area by 2015. The goal of the plan is to reduce Caspian tern predation on out-migrating juvenile salmonids (salmon and steelhead) in the Columbia River estuary, and thereby enhance recovery of salmonid stocks from throughout the Columbia River basin. Thirteen of 20 evolutionarily significant units (ESUs) of Columbia Basin salmonids are currently listed as either threatened or endangered under the U.S. Endangered Species Act (ESA).

The Caspian Tern Management Plan called for the creation of approximately 7-8 acres of new or restored Caspian tern nesting habitat (islands) in interior Oregon (specifically Fern Ridge Reservoir, Crump Lake, and Summer Lake) and the San Francisco Bay area (specifically Don Edwards National Wildlife Refuge, Hayward Regional Shoreline, and Brooks Island) and to actively attract Caspian terns to nest at these sites. As alternative tern nesting habitat is created or restored, the available tern nesting habitat on East Sand Island will be reduced from its current size (approximately 5 acres) to 1.0 -1.5 acres.

Creation of tern nesting habitat at alternative colony sites and the reduction of nesting habitat at East Sand Island was planned to occur in phases, at a ratio of two new acres of habitat provided for each acre of habitat reduction on East Sand Island. Once fully implemented, the management plan was expected to reduce the East Sand Island Caspian tern colony from its current size (approximately 10,000 nesting pairs) to about 3,125 – 4,375 nesting pairs, or a reduction in colony size of 60% - 70%. A reduction in the size of the East Sand Island Caspian tern colony to 3,125 – 4,375 pairs was estimated by NOAA Fisheries to increase the annual population growth rate of three ESA-listed ESUs of Columbia Basin steelhead by 1% or greater. Steelhead were the focus of NOAA Fisheries’ analysis because previous studies had indicated that Caspian tern predation rates on juvenile steelhead exceeded those of other salmonid species in the Columbia Basin. The planned reduction in the size of the Caspian tern colony at East Sand Island was expected to reduce annual consumption of juvenile salmonids (smolts) from the Columbia River basin by about 3.0 million fish. Annual consumption of juvenile salmonids by Caspian terns during the period 2000-2009 has averaged approximately 5.5 million smolts per year.

The potential for reduction in Caspian tern nesting habitat at East Sand Island to 1 acre is addressed in the 2006 RODs. Before nesting habitat on East Sand Island could be reduced below 1.5 acres, however, additional alternative sites for tern nesting would need to be developed (the criteria for selection of alternative sites were described in Appendix G of the FEIS). Two additional sites in northeastern California, Tule Lake National Wildlife Refuge and Lower Klamath National Wildlife Refuge, were recently identified as part of this on-going process and environmental assessments were prepared for each site prior to island construction late in 2009 and early in 2010. A reduction in the size of the East Sand Island tern colony to 2,500 - 3,125 pairs could eventually be accomplished with development of these alternative tern colony sites.

The USACE and its state and federal partners have so far completed construction of eight islands (a total of 7.3 acres) specifically designed for Caspian tern nesting as part of the Caspian Tern Management Plan. Two one-acre islands were built prior to the 2008 breeding season (Fern Ridge Reservoir and Crump Lake), two half-acre islands were built prior to the 2009 breeding season (East Link Management Unit and Dutchy Lake in Summer Lake Wildlife Area), and four additional islands were built prior to the 2010 breeding season (a half-acre island at Gold Dike impoundment in Summer Lake Wildlife Area, a one-acre island at Orems Unit and a 0.8-acre island at Sheepy Lake in Lower Klamath NWR, and a two-acre island at Tule Lake Sump 1B in Tule Lake NWR). A minimum of six of the eight islands constructed to date (6 total acres of nesting habitat) will be available for tern nesting during the 2011 breeding season; the islands at Gold Dike (Summer Lake Wildlife Area) and  Orems Unit (Lower Klamath NWR) may not be surrounded by water in 2011 and therefore would not be unsuitable for tern nesting during that year. As stipulated in the FEIS and RODs, the amount of habitat prepared for tern nesting on East Sand Island will be reduced from 3.1 acres in 2010 to 2 acres in 2011.

In 2010, Caspian terns quickly colonized the new 0.8-acre floating island at Sheepy Lake in Lower Klamath National Wildlife Refuge, where 258 pairs raised 168 young. Nineteen terns that had been banded in the Columbia River estuary were re-sighted at the Sheepy Lake tern island. We continued to monitor four other alternative colony sites constructed by the USACE in interior Oregon in 2008 and 2009. No Caspian terns successfully nested at three of these four islands and the fourth (East Link Management Unit in Summer Lake Wildlife Area) experienced very low nesting success, apparently due to adverse weather conditions and low forage fish availability during the 2010 nesting season. The diet of Caspian terns nesting at these sites consisted of > 80% tui chub, crappie, and bass.

Future Caspian Tern Management Actions

In partnership with East Bay Regional Parks, the USACE plans to enhance the habitat on an existing island in a former salt pond at Hayward Regional Shoreline prior to the 2012 nesting season, in order to create an additional one acre of suitable nesting habitat for Caspian terns in southern San Francisco Bay. Construction of a tern island at Malheur National Wildlife Refuge is also in the early planning stages and may be completed in the coming years. 

The main driver behind the plan to relocate a majority of the Caspian terns that currently nest at the colony on East Sand Island in the Columbia River estuary is to increase the survival of juvenile salmonids from throughout the Columbia River basin. There are, however, significant benefits to the Pacific Coast population of Caspian terns that may be realized by implementation of the Caspian Tern Management Plan. Currently, approximately two-thirds of all Caspian terns belonging to the Pacific Coast population nest on East Sand Island. Consequently, the tern population is more vulnerable to local catastrophes (for example, storms, disease outbreaks, oil spills, predation events, human disturbance) than it would be if it were distributed over a broader geographic area and a larger number of nesting sites. Redistributing the existing breeding population of Caspian terns to a number of smaller colonies over a larger geographic area will reduce risks to both terns and Columbia Basin salmonids. Close monitoring of this plan throughout its implementation is necessary to determine whether the intended benefits to both salmonids and terns are realized and, if not, what adaptive modifications to management actions may be warranted to achieve desired results.