Razorback Sucker in Lake Mead, Arizona and Nevada: young , resilient, and recruiting

1. Razorback Sucker in Lake Mead, Arizona and Nevada: young, resilient, and recruiting Zachary Shattuck, Brandon Albrecht, Ronald Kegerries, Ronald Rogers, and Paul Holden

2. Acknowledgements Lake Mead Workgroup

3. Objectives • Habitat use and life history characteristics • Sampling efforts for all life stages • Population size and age structure • Use of known spawning sites (long-term monitoring) • Search for new population concentrations (Colorado River inflow)

4. Overview and Background • Long-term monitoring study (LTM) • 15 years of study (1996-2011), in 16thyear (2012) • Through 2011: 814 captures, 325 recaptures • Through 2011: 367 aged, 2-36 years old • Established reproduction in: • Las Vegas Bay (LB) • Echo Bay (EB) • Virgin River/Muddy River inflow (OA)

5. Overview and Background • Colorado River inflow study (CRI) • 2 years of study (2010-2011), in 3rd year • Through 2011: 30 captures, 8 recaptures • Through 2011: 12 aged, 6-11 years old • Established reproduction in: • Colorado River inflow (CI)

6. Methods and Study Area • Sonic telemetry • Trammel netting • Larval sampling • Age determination • Population estimation LTM CRI

7. Lake Mead Conditions • 1,092 ft – January 2011, 1,131 ft – March 2012

8. Lake Mead Conditions 2005/2011 • Heavy winds and Large woody debris, bad for props

9. Sonic Telemetry 2010-2011 LTM • 351 active contacts (13 individuals) • 8 new sonic-tagged individuals stocked 1/2011 (4-LB, 4-OA) • 5 from 2008 individuals • 2 passive contacts by 2 SURs • Difficulties with tracking inflows • Las Vegas Wash, Virgin River/Muddy River inflow • Demonstrated connectivity between LTM and CRI sites

10. Sonic Telemetry 2010-2011 CRI • 302 active contacts (18 individuals) • 4 new sonic-tagged individuals stocked 1/2011 • 9 from 2010 individuals, 1 from 2008 individuals • 42,206 passive contacts by 2 SURs • Tracking inflow with CART tags • 4 new sonic/radio-tagged individuals used to track movement in Colorado River • Heavy seasonal use of river/lake interface, limited upstream movement in river • Helped identify 2011 spawning area

11. Adult Sampling 2010-2011 CPUE Colorado River Inflow

12. Adult Sampling 2010-2011 LTM • 67 net-nights = 86 total captures (14 recaptures) • Las Vegas Bay (24 net-nights, 9 captures [1 recapture]) • 50% F, 50% M, 5 subadults • 2011 CPUE = 0.43 fish/net-night • Echo Bay (24 net-nights, 15 captures [6 recaptures]) • 26.67% F, 73.33% M • 2011 CPUE = 0.63 fish/net-night • Overton Arm (21 net-nights, 62 captures [7 recaptures]) • 53.23% F, 46.77% M • 2011 CPUE = 2.82 fish/net-night, record high CPUE • 2 flannelmouth suckers (*LB, OA)

13. Adult Sampling 2010-2011 CRI • 187 net-nights = 15 total captures (8 recaptures) • 40% F, 60% M • 2011 CPUE = 0.08 fish/net-night • Razorback sucker x flannelmouth sucker hybrids • 7 captures (1 recapture) • Flannelmouth sucker • 112 captures (39 recaptures) • 1 bluehead sucker* • Success of a variety of efforts in river have been limited

14. Adult Sampling 2010-2011 • Green River = 2.2 mm/year1 LTM Wild = 19.3 mm/yearLTM Stocked = 35.5 mm/year Lake Mead = 24.7 mm/year CRI Wild = 12.4 mm/yearCRI Stocked = 34.4 mm/year • Lake Mohave = 5.0 mm/year2 1Tyus 1987; 2Minckley 1983

15. Larval Sampling 2010-2011 LTM • 4,288 collected from combined sites • Las Vegas Bay (449 collected in 1,590 min) • CPM = 0.282, • majority on S shore (2/24 – 4/12 at 15-21°C) • Echo Bay (3,818 collected in 2,577 min) • CPM = 1.482, • majority on N shore (3/1 – 4/26 at 12-19°C) • Overton Arm (21 collected in 1,596 min) • CPM = 0.013, • majority on NW point of Meadows area (3/22 – 4/27 at 14-20°C)

16. Larval Sampling 2010-2011 CRI • 65 razorback sucker larvae collected in 8,760 min • CPM = 0.0074 • First collected 2/14/11 at 11.5 °C • majority in Lunch Cove (4/14 – 4/27 at 13-19°C) • Similar CPM for inaugural seasons at OA • 11 flannelmouth sucker larvae collected • CPM = 0.0013

17. Aging & Recruitment LTM • 367 individuals aged to date, 73 aged in 2011 • 72.6% (n = 53) were 7 years or younger • Remaining (n = 20) were aged 8-12 years • Oldest individual (12 years), TL = 574mm • Youngest individuals (3 years), TL = 383 mm • Strong year-class for 2005

18. Aging & Recruitment CRI • 10 individuals aged to date, 7 aged in 2011 • Ranged in age from 6-11 years • Age classes correspond closely with lake-wide recruitment • Oldest individual (11 years), TL = 659 mm • Youngest individuals (6 years), TL = 545 mm

19. Aging & Recruitment

20. Aging & Recruitment

21. Discussion • 2011 was exceptional for both LTM and CRI • Record adult catch rates in OA • Increases in effort at CRI greatly improved catch rates • Successful spawning at CRI, 2nd consecutive year • Unique population at Lake Mead • young, recruiting, and resilient • Potential for other population aggregates at Lake Mead • 2011 population estimate increasing, ~1000 • EB & OA: 737-1568 • LB: 107-167 • Lake-wide: 733-1038

22. Discussion • Recruitment occurs at a variety of lake levels • Presence of new, wild individuals near annually • Hybridization of native sucker documented at CRI • The potential effects of hybridization to the Lake Mead razorback sucker population is unknown • Opportunity with subadults • With potential for increased recruits, it could be an advantageous time to study this life stage • 2005 year-class • Ideal conditions for strong recruitment in 2005, 2011? • Exponential increase in numbers of potential recruits for 2017?

23. To date: 108 wild, young, sexually immature (subadult) razorback sucker collected at Lake Mead 1996-1997 (2 yrs) = 4 subadults 1998-2005 (8 yrs) = 17 subadults 2006-2011 (6 yrs) = 86 subadults 2012 = 1 subadult thus far

24. 2011-2012 Update • Subadult sonic-tagging • Pilot study to describe habitat use and seasonal movement of this life stage • 1 wild subadult has been tagged and is being monitored with hopes for additional subadults • Use of inundated vegetation as cover in turbid areas of Gypsum Wash and Las Vegas Wash • LTM 2012 = 41 captures (16 recaptures) • CRI 2012 = 23 captures (13 recaptures)

25. Thank You!