Abundance, habitat selection and potential for fish predation by Common Mergansers on the Trinity Ri

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Abundance, habitat selection and potential for
fish predation by Common Mergansers on the
Trinity River.
C. John Ralph, Sherri Miller and Pablo Herrera
USFS Redwood Sciences Laboratory
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MAINSTEM - TRINITY RIVER 63-KM Restoration Area
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? Raft or Kayak 30 km / day ? May Oct, One
survey per month ? Scale 16 reaches, survey
300 m sections of 40 miles below dam ? Species
Age --Count Activity Perch Location
relative to water
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Photos by Peter LaTourrette
WE DETECT gt80 OF BIRDS ALONG RIVER --- WE
ACCOUNT FOR FLUSHING
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Generalized Aquatic Bird Life Cycle
Quality and quantity of food fish and
invertebrates and amphibians. Human activities
construction, disturbance, avoidance.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov
Dec
Quality and quantity of nest substrate/site, nest
cavities. Human activities construction,
disturbance, avoidance.
Quality and quantity of food fish and
invertebrates and amphibians. Human activities
construction, disturbance, avoidance. Predator
density raptors, mammalian.
Quality and quantity of food fish and
invertebrates and amphibians. Predator density
raptors, mammalian. Quality and quantity of
habitat water, dense willows, aquatic edge cover.
Quality and quantity of food fish and
invertebrates and amphibians. Predator density
raptors, mammalian (Merganser-flightless
period).
Quality and quantity of food fish and
invertebrates and amphibians. Predator density
raptors, mammalian (Merganser-flightless
period).
Quality and quantity of food fish and
invertebrates and amphibians. Quality and
quantity of habitat water, dense willows,
aquatic edge cover.
Overwinter survival
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YOUNG OTHERS AND ADULTS
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ABUNDANCE OF HABITAT ALONG RIVER
RUN RIFFLE POOL
LENGTH (KM)
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PERCENT OF HABITAT ALONG RIVER
RUN RIFFLE POOL
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POTENTIAL FISH TAKE BY MERGANSERS IN TRINITY RIVER

• MERGANSERS REQUIRE 220-750 g / DAY 500 g
• IF AVERAGE FISH IS 10-20g, ABOUT 20-50 FISH /
  DAY TAKEN PER BIRD
• ALLOWING FOR MISSED MERGANSERS, ABOUT 200-400
  BIRDS IN 40 MILES OF RIVER AT ONE TIME
• TOTAL DAILY TAKE ABOUT 2,000-8,000 FISH
• TOTAL FISH PER SEASON TAKEN IS 1 TO 3 MILLION
  OVER NINE MONTHS
• IF INCLUDE REST OF TRINITY, IMPACT IS DOUBLE

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POTENTIAL FISH TAKE BY MERGANSERS IN TRINITY RIVER

• MERGANSERS REQUIRE 220-750 g / DAY 500 g
• IF AVERAGE FISH IS 10-20g, ABOUT 20-50 FISH /
  DAY TAKEN PER BIRD
• ALLOWING FOR MISSED MERGANSERS, ABOUT 200-400
  BIRDS IN 40 MILES OF RIVER AT ONE TIME
• TOTAL DAILY TAKE ABOUT 2,000-8,000 FISH
• TOTAL FISH PER SEASON TAKEN IS 1 TO 3 MILLION
  ANNUALLY.
• INCLUDE REST OF TRINITY AND WINTER, IMPACT IS
  MORE THAN DOUBLE THIS PERHAPS 5 MILLION

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Next Steps to Improve Model

• ? Model relationships between abundance and river
  and riparian habitat characteristics.
• Acquire fish abundance and seasonal changes,
  including hatchery releases, for analyses
• Examine annual and seasonal trends as the
  monitoring continues through the restoration
  construction and management
• Determine where in river is largest take of
  young fish
• Determine percent of various fish species taken
  using stable isotopes and other methods
• Need population estimates of mergansers in spring
  and when smolt leaving in spring

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Next Steps to Improve Model

• ? Model relationships between abundance and river
  and riparian habitat characteristics.
• Acquire fish abundance and seasonal changes,
  including hatchery releases for analyses
• Examine trends as the monitoring continues
  through the restoration construction and
  management
• Where in river is biggest danger to young?
• Food habits, look for percent of species in
  droppings
• Need population of mergansers when young fish
  overwinter and leaving in spring