POPULATION CHARACTERISTICS OF THE CRITICALLY ENDANGERED WESTERN GRAY WHALE Amanda L. Bradford A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2011 Program Authorized to Offer Degree: School of Aquatic and Fishery Sciences
University of Washington Graduate School This is to certify that I have examined this copy of a doctoral dissertation by Amanda L. Bradford and have found that it is complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made. Chair of the Supervisory Committee: Glenn R. VanBlaricom Reading Committee: André E. Punt Glenn R. VanBlaricom David W. Weller Date:
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University of Washington ABSTRACT POPULATION CHARACTERISTICS OF THE CRITICALLY ENDANGERED WESTERN GRAY WHALE Amanda L. Bradford Chair of the Supervisory Committee: Associate Professor Glenn R. VanBlaricom School of Aquatic and Fishery Sciences The western population of gray whales (Eschrichtius robustus) has not recovered from past exploitation and is listed as critically endangered. Current anthropogenic threats and environmental conditions may be limiting western gray whale recovery, warranting an examination of the magnitude and influence of these factors. Estimates of demographic parameters are also needed to characterize the population and quantify its status. Western gray whales have been monitored since 1997 on their primary feeding ground off the northeastern coast of Sakhalin Island, Russia. This effort resulted in a large dataset of photo-identification images of 169 individual whales that was used to quantify anthropogenic scarring, visually assess body condition, and estimate markrecapture and other population parameters of western gray whales. In total, 24.3% (n=41) of identified individuals were determined to have been previously entangled in fishing gear at least once and 1.8% (n=3) were found to have survived at least one vessel collision. Body condition improved significantly as each feeding season progressed, but years of significantly better and worse body condition were identified. The body condition of lactating females was significantly worse than that of other whales at all times, but the body condition of their weaning calves exhibited no temporal variation and
was consistently good. A significant male-bias in the calf sex ratio could not be linked to observations of maternal condition and other reproductive characteristics, but differential pre- or postnatal mortality of female calves could account for the sex ratio bias and lack of explanatory power. The first observed values of western gray whale age at first reproduction are seven and 11 years. Non-calf survival did not differ between males and females and was estimated as 0.973 (SE=0.007, 95% CI=0.954-0.984), with calf survival significantly lower at 0.717 (SE=0.063, 95% CI=0.579-0.824). Abundance estimates revealed that a maximum of 140 whales were associated with the Sakhalin feeding area by 2007. Recent movements of some Sakhalin individuals into the eastern Pacific suggest that this value may overestimate the number of gray whales that migrate and breed in Asian waters. That is, the critically endangered western gray whale population may be even smaller than presently recognized.
TABLE OF CONTENTS Page List of Figures... iv List of Tables... vi Chapter 1: Anthropogenic scarring of western gray whales...1 Introduction...1 Methods...3 Results...7 Inter-rater agreement...7 Anthropogenic scarring...8 Expert review...9 Discussion...10 Inter-rater agreement and expert review...10 Anthropogenic scarring...11 Significance...16 Chapter 2: Chapter 3: Chapter 4: Comparing observations of age at first reproduction in western gray whales to estimates of age at sexual maturity in eastern gray whales...23 Introduction...23 Methods and results...25 Discussion...26 Leaner leviathans: body condition variation in a critically endangered whale population...34 Introduction...34 Methods...39 Whale sighting data...39 Body condition assessment...40 Statistical analysis...43 Results...44 Discussion...46 Do observations of maternal condition explain the male-biased calf sex ratio of western gray whales?...66 Introduction...66 Methods...70 Individual whale and body condition data...70 Statistical analyses...72 Calf sex ratio bias...72 i
Associations between maternal condition and calf sex...72 Sex-specific reproductive costs...74 Reproductive female body condition dynamics...75 Reproductive tendencies of individual females...76 Results...77 Discussion...79 Chapter 5: Chapter 6: Survival and abundance of western gray whales off Sakhalin Island, Russia...97 Introduction...97 Methods...101 Photo-identification surveys...101 Mark-recapture analyses...102 Non-calf and calf survival...103 Male and female survival...105 Abundance estimation...106 Analytical assumptions...108 Results...109 Non-calf and calf survival...109 Male and female survival...111 Abundance estimation...112 Discussion...113 Survival estimation...113 Abundance estimation...117 Application of estimates...119 Using barnacle and pigmentation characteristics to identify gray whale calves on their feeding grounds...130 References...141 Appendix A: Summary of updated anthropogenic scarring results, which incorporate 2006-2007 into the 1994-2005 time series....161 Appendix B: Report of an inter-rater agreement study that evaluated the comparability of results produced by two trained researchers using the body region scoring protocol developed to assess western gray whale body condition...162 Appendix C: Overview of sensitivity analyses conducted to confirm that month was an appropriate and feasible scale at which to collapse the numerical body region condition scores for the assessment of western gray whale body condition....165 ii
Appendix D: Monte Carlo simulation exercise conducted to examine if the exact trend test comparisons of western gray whale maternal condition, calf sex, and other reproductive parameters were robust to stochastic variation in sample observations...173 Appendix E: Comparison of models (n = 70) used to estimate western gray whale non-calf and calf survival from 1997 to 2007....178 Appendix F: Comparison of models (n = 28) used to estimate western gray whale male and female non-calf survival from 1997 to 2007....180 Appendix G: Yearly numbers of whales identified (n), estimates of individuals using the study area each year (N), temporary emigration probabilities (γ), and total population sizes associated with the study area (N o ) for whales 7-yr-old and <7-yr-old from 1997 to 2007 based on the robust design model φ(gc) γ(g7) p(t+res)....181 Appendix H: Yearly numbers of whales identified (n), estimates of individuals using the study area each year (N), temporary emigration probabilities (γ), and total population sizes associated with the study area (N o ) for whales 4-yr-old and <4-yr-old from 1997 to 2007 based on the robust design model φ(gc) γ(g4+t) p(t+res)...182 iii