Markus Horning Dept. Fisheries & Wildlife Marine Mammal Institute Oregon State University

1. Chronicle of a death re-told:quantifying predation on juvenile Steller sea lions in the Gulf of Alaska Markus Horning Dept. Fisheries & Wildlife Marine Mammal Institute Oregon State University Jo-Ann Mellish University of Alaska Fairbanks Alaska Sea Life Center

2. Wanted for Steller sea lions:life-long, spatially & temporally explicit data on: • forage (dive) effort • survival • emigration • causes of mortality in individuals • Impact of predation on near apex mesopredators is ‘empirically intractable’ • Williams et al. “Killer Appetites” Ecology 2004 • The Life History Transmitter (LHX tag) • Horning & Hill IEEE J. Oceanic Engineering 2005 (with Wildlife Computers, Redmond, WA)

3. The Life History Transmitter

4. The Life History Transmitter implanted records data through entire life of animal

5. Host has died, where, when, why, cumulative weekly dive effort Dual tagging: - to determine failure rate- derive correction factor

6. Results of control & validation studies 25 sea lions released with LHX tags since 2004 - 4 Z. californianus (TMMC, California) - 21 E. jubatus (ASLC, Alaska)Horning et al. BMC Vet. Res. 2008 Captive period clinical responses: ↑ lympho- & monocytes, globulins, haptoglobins ↓ baseline by ≤ 45 daysMellish et al. JEMBE 2007 Post-release external tracking 2-6 months: - No differences in diving, ranging behavior - Min. confirmed post-procedure survival for 264d (72 - 932 n=15 E.j, sem 72.3)Thomton et al. End. Spec. Res. 2008

7. Preliminary Results • 21 juvenile Steller sea lions in PWS / KF – 8492 days • n=12 male juveniles →6 tags from 4 animals in 4898 days • 1 xmit from each event + 2 beach recoveries: 0.25 ≤ Pf ≥ 0.5 1 undetected mortality for 4 detected events → 5 deaths • Estimated MSR Yr 1-3: 35.7% (0.15-0.86)Yr 1-4: 31.1% (0.12-0.84) (Mayfield Wilson Bull. 1961 - Johnson Auk 1979) • Brand re-sight based MSR for Seal Rocks – PWS NMML data (L. Fritz, R. Towell) 143 males x 4 yrs (2001-05) Yr 1-3: 36.5%(0.25 - 0.49) Yr 1-4: 29.0%(0.17 - 0.43) • Within limits of n, d:no mortalities missed; no mortalities caused

8. Preliminary Results • LHX tag DATA from 4 events • one event with incomplete data

9. Preliminary Results

10. Preliminary Results (calc.: Henssge 1988 Forensic Sci. Int.)

11. Preliminary Results • LHX tag DATA from 4 events • one event with incomplete data • three events likely acute / traumatic death: - temperature profiles - onset of transmissions at next opportunity - two data sets: ‘normal’ divinguntil date of death - one animal ‘normal’ appearance, movement (remote video) • at least 3 of 4 detected mortalities: Predation – likely by killer whales is single greatest cause of mortality for juvenile Stellers in PWS-KF • 51.5% of females (42.7–59.6) consumed before primiparity(predation of 3/4 @ age 2 -20% p.a. & NMML ASR data)

12. Consummate and consumed predators • Impact of killer whale predation on Steller sea lion population trajectories? • Dependent on prevalence of predationin relation to productivity! • The predator pit conceptual framework- based on density dependent type III functional response- assumes prey shifting • C. S. Holling Can. Entomol. 1959 • A. Bakun Progr. Oceanog. 2006 • Horning & Mellish Frontiers in Ecology & Environment - in Review

13. Consummate and consumed predators

14. Consummate and consumed predators • How applicable is the predator pit conceptual framework? • Has substantial qualitative explanatory power! ↔ ↕ • Suggests that western SSL are in refuge of predator pit: • 20% of peak abundance • Neutral population trajectory • Recent increases in juvenile survival • Predation rates may have been higher, may re-occur • Recent decrease in natality may relate to: • 1) High former juvenile predation → 2) reduced recruitment→ 3) shift in age structure to older femalesReproductive senescence?Natality from pup / non-pup ratios could be due to 1) & 3) • Lunn et al. J. Anim. Ecol. 1994; Beauplet et al. OIKOS 2006 • Holmes et al. Ecol. Applications 2007

15. Consummate and consumed predators • Future directions: • Needs - spatially explicitdata for multiple species on: • Mortality & predation • Productivity • Predator prey habits • LHX tags are spatially explicity viable tool for 1 (2)

16. Acknowledgements • Roger Hill (Wildlife Computers) • Marty Haulena (TMMC, Vanc Aq), Pam Tuomi (ASLC) • Lowell Fritz, Rod Towell (NMML) • Funding through: • North Pacific Marine Research Program • Pollock Conservation Cooperative Research Program • Steller Sea Lion Research Initiative (NOAA) • Alaska Sea Life Center • North Pacific Universities Marine Mammal Research ConsortiumNMFS Permits # 1034-1685 & #881-1668/1890