Orca mothers endure a lengthy pregnancy of one and a half years, followed by up to two years of nursing, and then continue to provide for their adult offspring, who remain with them for life.
These maternal responsibilities take a toll on orca mothers, as highlighted by Sharon Kay, a biologist and author of recent research published in the journal Scientific Reports. The study delves into the physical effects of motherhood on orcas, focusing on body fat levels, a crucial indicator linked to survival in these marine mammals.
The research reveals that the speed at which mothers regain body fat after pregnancy is dependent not on the number of births but rather on the number of offspring that they continue to care for.
Experts emphasize that these findings shed light on the societal pressures faced by orcas, amidst ongoing human disturbances in their habitat.
Examination of Northern Resident Killer Whales
The study focuses on northern resident killer whales, whose habitat stretches from Alaska through the coastal waters of British Columbia to northern Washington. These whales are categorized as threatened under Canada’s Species at Risk Act.
Amy Rowley, a biologist with the Raincoast Conservation Foundation and a co-author of the study, explains that after giving birth and initiating nursing, orca mothers experience a significant decline in body fat levels. This decline persists for about three years, with some mothers struggling to return to their pre-pregnancy condition.
To assess the changes in body fat levels, the research team utilized drones to capture images from 30 meters above the whales, focusing on the fat reserves located behind their heads.
The analysis involved scrutinizing the white patches above the whales’ eyes pixel by pixel to track fluctuations indicating their body condition.
Rowley explains, “A whale with outward-angled eye patches signifies a healthier, fatter state, whereas parallel or inward-angled patches suggest lower fat reserves and potentially poor health.”
Impact of Offspring on Body Fat Levels
By studying 66 adult female whales, the researchers identified that the number of living offspring has the most significant impact on body fat levels. (Nearly half of killer whale calves do not survive beyond the first year.)
Kay notes, “It’s not just the act of nursing and reproducing that takes a toll on the mothers, but also the lifelong responsibility of finding and sharing food with their offspring.”
Hannah Myers, a marine ecologist at the University of Alaska Fairbanks, commends the study for contributing valuable insights into the social dynamics of these creatures, made possible through long-term monitoring programs and innovative technologies.
