A study explores how additive mortality events affect social systems of killer whales. Sociality among highly social top predators tends to enhance group member survival by improving fitness and foraging opportunities, but such social systems can be disrupted by catastrophic events. Marine Busson and colleagues analyzed the social networks of 221 killer whales encountered on 6,087 occasions between 1987 and 2014 and assessed how severe mortality due to interactions with illegal fishing vessels between 1996 and 2002 affected killer whales of the Crozet Islands in years following the end of illegal fishing. The loss of individuals from a group resulted in weaker associations among surviving individuals, compared with associations detected from the pre-illegal fishing period. The authors also found a positive correlation between survival probability and social group size, although association strength was a stronger indicator of survival. Following the seven-year period of severe mortality, 98 individuals from social groups known prior to the illegal fishing period did not re-associate in stable social groups. The whales' survival rate declined, leading to a population decline from 98 individuals to 37 individuals. The findings suggest that the disruption of social groups caused by human-induced additive mortality events may result in long-term negative consequences, according to the authors.
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Article #18-17174: "Role of sociality in the response of killer whales to an additive mortality event," by Marine Busson et al .
MEDIA CONTACT: Marine Busson, University of La Rochelle, FRANCE; tel: +33-674410064; email: marine.busson94@gmail.com ; Paul Tixier, Deakin University, Melbourne, AUSTRALIA; tel: +61-484122796; email: p.tixier@deakin.edu.au
Proceedings of the National Academy of Sciences