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Identifying and Mapping Potential Kokanee Spawning Habitat in Lake Pend Oreille

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Kokanee, the land-locked form of sockeye salmon (Oncorhynchus nerka), were introduced to northern Idaho’s Lake Pend Oreille in the 1930s. For over 30 years, kokanee supported a highly productive commercial and sport fishery and became an important forage species for, among other predators, the threatened native bull trout (Salvelinus confluentus). Since the 1960s, the kokanee population in the lake has declined sharply because of spawning habitat loss and other factors. In 2000, the kokanee harvest was closed.

Kokanee in Lake Pend Oreille, Idaho
Kokanee (Oncorhynchus nerka) in Lake Pend Oreille, Idaho. Photo by USGS.

How the USGS Helps

The objectives of this project are to:

  • Survey the lakebed in the spawning habitat
  • Determine the particle size of spawning habitat
  • Determine the embeddedness of gravels and cobbles on the lakebed
  • Create bathymetric maps using geographic information systems (GIS)
  • Compute the area of mapped “clean” gravel available for kokanee spawning
  • Evaluate the methods used to determine their viability for mapping the rest of the lake

Key Findings

  • Based on general spawning substrate preferences, areas of lakebed with embeddedness of greater than 15 percent were classified as the geologic unit Qsltsd, “embedded lakebed.”
  • Substrate characteristics assumed to be most preferred by spawning kokanee may be found in the geologic unit Qfmg, “fine-medium gravel lakebed,” where very-fine-to-medium gravel composes more than 50 percent of the lakebed with or without lesser amounts of coarse gravel and cobble
  • Kokanee also may find suitable spawning substrate in the geologic unit Qcg, “coarse-gravel lakebed,” where coarse and very coarse gravel compose the largest percentage of clasts in this unit
  • Substrate characteristics that spawning kokanee may avoid are in the geologic unit Qc, “cobble lakebed,” where cobble and coarse gravel compose the largest percentage of the clast size
  • Lakebed with significant amounts of both fine-medium gravel and coarse gravel and cobble were mapped as the undifferentiated, geologic unit Qgcu

Products

Barton, G.J., and Dux, A.M., 2013, Bathymetry, morphology, and lakebed geologic characteristics of potential Kokanee salmon spawning habitat in Lake Pend Oreille, Bayview and Lakeview quadrangles, Idaho: U.S. Geological Survey Scientific Investigations Map 3272, 1 sheet.