Background/Objectives Determine population size of Lake Mead razorback sucker. Document Lake Mead habitat use and life history characteristics. Document use of known spawning sites. Conduct sampling efforts for all life stages. Conduct long-term monitoring (1996-2012). Search for new population concentrations (i.e., Colorado River Inflow Area). WILD FISH!
Methods Sonic telemetry (active and passive) Trammel netting Larval sampling Nonlethal age determination (fin rays) Population estimate
2011 Long-term Monitoring 67 total net-nights (January–April 2011) 86 total captures, 14 recaptures (16.3%) = 72 new/wild captures 600+ captured and tagged to date 73 individuals aged 360 aged to date 72.6% (n = 53) were 7 years or younger Strong year-class for 2005 Total of 4,288 larval razorback collected from long-term monitoring sites 5 wild juveniles
To date: 107 wild, young, sexually immature (subadult) razorback sucker collected at Lake Mead. The trend: 1996–1997 (2 years) = 4 subadults 1998–2005 (8 years) = 17 subadults 2006–2011 (6 years) = 86 subadults
Recruitment nearly every year! Strong recruitment pulse around 2005; these fish are now adults. Expect recruitment to continue past 2008.
Lake Mead Conditions, 2005 and 2011 Heavy winds and Large woody debris, bad for props
Lake Mead Conditions Started at 1,092 ft. Jan 2011 and rose to 1,134 ft. Strong year class for 2011? Hope for the future!
Colorado River Inflow First Rapid Second Rapid North Beach “Lunch Cove” 2011 spawning area 2010 spawning area
Sonic-tagged fish enhanced our ability to capture wild razorback suckers, helped identify the 2011 spawning area, and increased our efficiency. Limited upstream movement - fish stocked upstream returned to the lake. Radio technology was useful but became irrelevant. Telemetry Summary
CRI Adult Sampling Total of 187 net nights (600% increase from 2010). Total of 15 razorbacks (8 recaptured, 7 new wild fish). Total of 7 hybrids [razorback x flannelmouth] (1 recaptured, 6 new wild fish). Total of 112 flannelmouth (39 recaptured, 73 new wild fish). 0.08 razorback/net night (0.04 new, wild fish/net night). Single bluehead sucker also captured.
CRI Larval Collections Total of 265 sampling events for a total of 146 light hours. First larval razorback sucker collected (Feb 14, 2011; temp 11.5° C). Total catch of 65 larval razorback suckers (350% increase from 2010). Captured 11 flannelmouth larvae for a CPM of 0.0013. Catch per minute (CPM) value for razorback sucker larvae similar to those observed initially at MR/VR inflow. CRI important spawning location for native suckers.
Razorback Sucker Aging Ages ranged from 6 to 11 (2000 – 2005)
CRI Conclusions Successful spawning has been documented and confirmed for the past two field seasons. Wild, ripe razorback suckers were captured at different locations for two consecutive field seasons in the CRI. Sonic-telemetry techniques can be used as an effective tool to help document razorback sucker habitat use in understudied areas of Lake Mead. Hybridization of native sucker species has been documented.
Why Lake Mead? Unique population Young, recruiting, resilient Population estimate ~ 1000 fish Unique habitat Inflows – cover Unique opportunity Study recruitment (subadult fish) The importance of cover Positive outlook for an endangered species