Researchers from the University of Washington have reported a troubling pattern among southern and northern orcas off the coast of British Columbia. The study suggests that female matriarchs in the southern group are fewer in number and less able to lead their kin, a factor that may help explain why the northern population is increasing while the southern group declines. Findings were published in the journal Behavioral Ecology.
The northern killer whales inhabit the northern waters of British Columbia in Canada, whereas the southern population ranges farther south. In recent years, the southern group has faced high rates of miscarriage and calf mortality, with only a small portion of pregnancies resulting in viable offspring. Current estimates place the southern population at around 73 individuals, making it one of the most vulnerable orca groups in the region.
In contrast, the northern population has continued to grow, with more than 300 individuals recorded. The two groups share many ecological features: comparable habitat conditions and a diet that centers on salmon. Yet their fates diverge sharply, prompting researchers to consider social and reproductive dynamics as a key driver of population trajectories.
Both populations are organized into clans led by elder females who have passed reproductive age and who actively support the hunting efforts of adult offspring. This social structure appears to influence feeding success and group coordination, reinforcing the importance of matriarchs across the species. In the observed period, scientists tracked changes in hunting efficiency and prey intake among individuals from 2009 through 2014, using longitudinal observations to capture shifts in behavior and success rates.
Among adult males in the south, hunting efficiency for salmon averaged higher than that of southern females, suggesting that male-assisted hunting might play a critical role for the southern group. Conversely, in the expanding northern population, the opposite pattern emerged: northern females captured significantly more salmon per hour than males, indicating a possible reinforcement of matriarchal influence as the population grows. This shift hints at evolving social dynamics tied to the availability of prey and reproductive pressures within each population.
The interpretation of these results points to potential differential access to prey for southern females. The data indicate that southern females may experience greater competition for food and, in some cases, direct predation pressure from males. In a subset of observed calves born to southern females, researchers found that successful provisioning by the mother was notably rare, underscoring the vulnerability of new offspring in environments with heightened competition for resources.
Experts emphasize that while the study highlights correlations between matriarch presence, hunting patterns, and calf survival, it does not fully establish causation. Ongoing observations are planned to determine whether the observed behavioral differences reflect a historical imbalance in female leadership within the southern clan and whether changes in matriarchal structure could influence future recovery or further decline for these orcas. The researchers stress the need to consider social organization alongside habitat quality and prey abundance when evaluating the prospects for both populations and when designing conservation strategies for northern British Columbia waters.