Year: 2004
Type: article
Abstract: The southern resident population of killer whales declined dramatically in the late 1990s. The number of animals in the population dropped from 97 in 1996 to 78 in 2001, a 20% decline in just five years. Although the reasons for this decline are unknown, external factors such as contaminant exposure, vessel interference, and low prey availability may contribute to the poor health and eventual mortality of the animals. My analysis examines two trends in southern resident mortality. Part 1 uses the percentage of mature males in a population as a surrogate for adult survival and compares the percentage of mature males in the southern resident population versus that of other populations of killer whales. My results indicate that the proportion of the southern resident population that is adult males is significantly lower than the percentage of adult males in the fourteen other populations sampled. I speculate that the high contaminant levels and increased\nnutritional stress of southern resident males led to this male-biased mortality. In the\nsecond part, I develop a method for visually assessing killer whale body condition using\nphotographs. Through 30 years of study, ten southern residents died as a result of\nemaciation. Of these, two individuals were characterized as “extremely thin” prior to\ndeath and four were described as “very thin.” Preliminary results indicate that conditions\ndescribed as worse than “thin” predict mortality. However, body condition of all\nmembers of the population fluctuates over time, suggesting that some population-wide\nfactor such as prey availability may influence body condition. Both of these techniques enable managers to track changes in the population over time, thus advancing our understanding of the fluctuating population dynamics of the southern resident\ncommunity.
Source: DukeSpace (Duke University)
Author: Kelsey Abbott
Language: English
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W192110957