Graduate Thesis Or Dissertation
 

Body Condition and Hormone Assessment of Eastern North Pacific Gray Whales (Eschrichtius robustus) and Associations with Ambient Noise

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  • Anthropogenic activities have posed many threats to the oceans and marine life. Understanding how individuals are affected and physiologically respond to these threats is crucial and allows for management and conservation applications. I evaluated the overall health condition of a subpopulation of gray whales (Eschrichtius robustus) along the Oregon coast, United States, throughout three consecutive foraging seasons (2016-2018). I used an innovative and multifaceted approach, assessing gray whale body condition through drone photogrammetry and stress responses through fecal hormone metabolite (glucocorticoids - GCm) analysis. I also assessed individual identification and steroid and thyroid hormone metabolites (progestins - Pm, androgens – Am, and thyroid - Tm) to account for confounding factors (i.e., age, sex, reproductive state) and investigate inter-relationships between hormone metabolites. I investigated possible associations between gray whale body condition and upwelling remote sensing data (as an oceanographic proxy for prey) and between hormone metabolite concentrations and body condition. Additionally, I also explored possible associations between hormone metabolite concentrations and ambient noise and vessel traffic. A total of 171 individuals were photo-identified, 289 drone flights were conducted, 158 fecal samples were collected, and 1,128 hours of acoustic data were recorded. Gray whale body condition changed according to demographic units, time and upwelling conditions. Calves and pregnant females displayed the best body condition while lactating females exhibited the poorest. Gray whale body condition was significantly better in 2016 compared to 2017 and 2018 when overall body depletion was observed. Relatively low upwelling conditions were detected in 2016 and 2017 when compared to the previous three years or 2018. I hypothesized that the period of poor prey availability caused carry-over effects between foraging success and body condition in subsequent years. As for the hormone metabolites (HM), higher mean Pm concentrations were observed in postweaning and pregnant females while mature males displayed the highest mean Am, GCm and Tm concentrations. All HM, with exception to Am varied by year. Positive correlations were observed between Pm and Am, and between GCm and Tm. I also estimated putative thresholds that indicate pregnancy, maturity in males, active reproduction in males, and stress-related concentrations in gray whales. When investigating possible associations between mature whale body condition (i.e., non-pregnant and non-lactating females) and HM concentrations associated with stress (cortisol) and energy allocation (cortisol and thyroid hormones), I observed that GCm concentrations were explained by body condition, sex, year, and Tm, while Tm concentrations were explained by body condition, sex, year, and GCm. I described a negative correlation between GCm and body condition, which indicates that a poor nutritional condition increases stress-related hormone concentration in gray whales. I also described a positive correlation between GCm and Tm, which may indicate an involvement with common metabolic activities, such as carbohydrate utilization. Lastly, I described a strong correlation between ambient noise and vessel traffic along the coasts of Newport and Depoe Bay, OR. Then, I compared vessel traffic at different temporal scales with GCm concentrations, while accounting for confounding factors. I demonstrated that vessel counts from the previous day of the sample collection and sex displayed significant effects on GCm concentrations. All of these physiological findings and associations to changes in the environment address data gaps on the field and advance our knowledge on baleen whale physiology. Furthermore, these findings can ultimately be used to inform decision-making policies regarding the management and conservation efforts.
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  • Pending Publication
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  • 2020-03-27 to 2022-04-28

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