Abstract 134 – Temporal Dynamics of Canine Breakage and Intraspecific Injuries in Western Hudson Bay Polar Bears (Ursus maritimus)

Simonne Tremblay, David McGeachy, Nicholas J. Lunn, Evan Richardson, Andrew E.
Derocher

Canine teeth are essential components of carnivore anatomy as they are utilized in prey
apprehension and behavioural displays; however, this tooth type has high incidences of injury
which may reduce survival. Polar bears (Ursus maritimus) typically have polygynous mating
systems where males compete for access to females. Injuries, especially to the canines, are
frequent in these encounters and can be used as proxies for mating system dynamics. The
western Hudson Bay (WHB) subpopulation has been experiencing decline in recent decades
which may impact characteristics of their mating system. We examine the overall patterns of
canine breakages and its temporal dynamics within the WHB using field data from 1981-2023
(n=3493) through non-parametric statistical analyses and linear mixed effect models. We found
differing rates of mean breakage and coinciding intraspecific injury between males and females;
proportions of maximum breakage are similar between the sexes until approximately ten years
of age, where males then begin accruing more serious damage to their canines. The interactive
effect between the age of an individual and the year of observation was a significant predictor
in mean breakage suggesting that breakage is beginning to increase over time. The comparative
results of canine breakage occurrences and related injuries between the sexes reveal WHB
males to be under more intensive intraspecific pressures than females within the
subpopulation, which aligns with previous research regarding canine breakage and its use in
understanding mating systems of polar bears. The presence of a relationship between year and
canine breakage in both sexes suggests that there may be increased intraspecific competition
occurring within the subpopulation, however continued investigation into the temporal
dynamics is required as stronger causal relationships are likely to arise as decline continues in
the subpopulation.