UW Aquatic & Fishery Sciences Quantitative Seminar
UW Aquatic & Fishery Sciences
Seasonal and Annual Variation in Body Condition of Western Gray Whales off Northeastern Sakhalin Island, Russia
The western gray whale population (Eschrichtius robustus) is critically endangered and its potential for recovery is uncertain. Along with other natural and anthropogenic threats, western gray whales are susceptible to nutritional stress, known from regular observations of individual whales in compromised body condition. Thus, the ability to visually quantify the relative body condition of free-ranging western gray whales and evaluate how this condition varies seasonally and annually is needed. A photo-identification study of western gray whales on their feeding ground off the northeastern coast of Sakhalin Island, Russia, produced a large dataset of digital, film, and video images of 149 identified individuals from 1997 to 2005. These images were utilized to visually assess the body condition (good, fair, or poor) of western gray whales by evaluating the relative amount of subcutaneous fat in three body regions presumed to reflect reductions in body condition. Findings from a qualitative exploration of the visual body condition determinations indicate that: 1) the body condition of whales varied annually and seasonally throughout the study period; 2) the body condition of whales generally improved during each field season; 3) lactating females were typically in compromised (fair or poor) body condition nursing calves that were almost always in good condition; and 4) individual variation in the body condition of both male and female whales is high. Logit models that can account for the multinomial response (body condition) and the correlated observations (individual whales) are currently being examined for use in the quantitative analysis. Investigating the causes and consequences of compromised body condition in western gray whales is important for understanding the health and viability of this population.