Idaho Department of Fish and Game

1
EVALUATE AND CONTROL BROOK TROUT POPULATIONS IN
NORTHCENTRAL IDAHO WATERSHEDS
ADDRESSING IMPACTS OF COMPETITION AND
HYBRIDIZATION WITH BULL TROUT

• Idaho Department of Fish and Game
• Clearwater Region
• Lewiston Idaho

2
ISSUES

• Brook trout may effectively displace or replace
  native bull trout through competition, predation,
  and hybridization.
• Downstream brook trout invasions may be the
  single most important negative impact to native
  bull trout in protected watersheds.
• Threats associated with hybridization may be more
  prevalent and important than previously
  documented.

3
PROTECTION OF NATIVE BULL TROUT

• Suppression of brook trout may be vital in
  protecting threatened bull trout in relatively
  protected watersheds

4
Are introduced, mountain lake populations of
brook trout negatively affecting downstream
populations of bull trout in watersheds of
northcentral Idaho?
5
OBJECTIVES

• Suppression of brook trout in mountain lakes and
  headwater tributaries.
• Document the distribution and abundance of bull
  and brook trout in Clearwater River drainage.
• Document hybridization of bull trout populations
  with brook trout.

6
Suppression Techniques
Sterile Tiger Muskies
Electrofishing
7
APPROACH

• Implementation and monitoring of suppression
  techniques.
• Snorkel survey methodologies to document
  distribution and abundance.
• Collection of genetic samples (using
  mitochondrial and nuclear DNA) to document
  hybridization.

8
WHAT WE KNOW TO DATE

• 50 headwater mountain lakes have naturally
  reproducing populations of brook trout.
• 40 of these lakes, are located within the
  Selway-Bitterroot Wilderness.
• Downstream invasions and colonization of brook
  trout is occurring.
• The distribution and abundance of both species is
  limited and uncertain.

9
PRODUCT

• Prioritization and development of brook trout
  suppression efforts.
• Documentation of introduced and native species
  distribution and interactions.
• Documentation and assessment of hybridization
  threats.
• Protection of native salmonids.