US Army Corps of Engineers
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Process overview: reproduction

Picture of bird and chickReproduction is the generation of offspring, which maintains plant and animal populations. Caspian terns (at right) rely on nesting habitat in the Columbia River estuary (photo courtesy Keith Larson, OSU). In 2002, nearly 10,000 breeding pairs nested on East Sand Island, which comprises approximately two-thirds of the west coast population of breeding adults (Myers et al. 2004).


Caspian terns feed on small fish, in particular juvenile salmonids leaving the estuary. The tern population in the Columbia River estuary was moved from Rice Island (river mile 21) to East Sand Island (river mile 5) in 2000 because studies indicated that the terns were consuming 10-12% of all young salmon that reached the estuary each year (Roby et al. 2003). This proximity to the mouth of the river has resulted in a shift in the terns diets to marine forage fish, with a 50% reduction in salmonid smolt mortality due to tern predation.


Structures that affect reproduction:

  • Scrub-shrub forest
  • Emergent marsh
  • Mud / sand flats
  • Submerged aquatic vegetation 

Ecosystem functions that are affected by reproduction:

  • Aesthetics / recreation
  • Biodiversity maintenance
  • Salmonid production
  • Other fish production
  • Avifauna production
  • Wildlife production

Contact information

Ronald Thom, Ph.D

Marine Research Operations, PNNL
1529 W. Sequim Bay Rd.
Sequim, WA 98382