The effect of age, sex, and resource abundance on patterns of rake markings in resident killer whales (Orcinus orca)

Abstract

Fluctuations in aggressive behavior of group‐living species can reflect social conflict and competition for resources faced by individuals throughout their lifespan and can negatively impact survival and reproduction. In marine mammals, where social interactions are difficult to observe, tooth rake marks can be used as an indicator of received aggression. Using 38 years of photographic data, we quantified the occurrence of tooth rake marks on wild resident killer whales (Orcinus orca), examining the effects of age, sex, and prey abundance on rake density. Our analysis revealed sex and age effects, with males exhibiting higher rake density than females and rake density declining significantly with age. Contrary to predictions, we observed an increase in rake density across the population as the abundance of their primary food resource, Chinook salmon (Oncorhynchus tshawytscha), increased. These results provide indirect evidence of fluctuations in received aggression from conspecifics across the lifespan of an individual, possibly reflecting changes in patterns of social conflict which may be mediated by resource abundance. Our findings highlight the need for further research to examine the fitness consequences of aggression in killer whales and to understand the proximate mechanisms by which resource abundance influences rates of aggression in the population.

Season, age, sex, and location impact the density of tooth rake mark and dorsal fin notch ofIndo‐Pacifichumpback dolphins (Sousa chinensis) in the northern South China Sea

“…Males exhibited the highest density of rakes and notches followed by unknown-sex dolphins and females, respectively. Such age-and sex-related patterns have previously been reported in other odontocete species, including killer whales (Grimes et al, 2022) and bottlenose dolphins (Lee et al, 2019;Marley et al, 2013). In addition, similar sex-related patterns have already been reported for IPHDs in Hong Kong and Taiwan (Wright et al, 2017).…”

“…Regarding prey availability, unexpectedly, Grimes et al (2022) reported an increase in rake density in killer whales as the abundance of their primary food resource increased. In addition, since dolphins hunt for mobile prey that is typically swallowed quickly and whole, they are not expected to compete for nor to share food (Mann & Sargeant, 2003).…”

Epidemiology of skin changes in endangered Southern Resident killer whales (Orcinus orca)

“…Alternatively, compensatory epidermal hyperplasia in response to the superficial lesion may facilitate virus replication. If either of these mechanisms are valid, the lower point prevalence in older females could be associated with older Southern Resident killer whale females having lower density of rake marks than other female age classes [ 56 ]. The rake-associated stage-class hypothesis, however, is not substantiated for calves.…”

“…The rake-associated stage-class hypothesis, however, is not substantiated for calves. Female Southern Resident killer whale calves experienced significantly higher rake density than all other female age categories [ 56 ] and male calves and male juveniles exhibited over twice the rake density of subadults and three times that of adult males [ 56 ]. While Geraci et al [ 93 ] suggest black pinpoint, grey and other lesions in dolphins are all progressions of poxvirus infection, currently, there is insufficient data to infer an etiology for these cutaneous lesions in Southern Resident killer whales.…”

Play fighting revisited: its design features and how they shape our understanding of its mechanisms and functions

“…During serious fighting, an attack is countered by a defense and if the combatants are equally matched in skill, few, if any, attacks reach their target (Geist, 1978), so much so, that the seeming rarity of injury often leads to serious fights being labeled as "ritualized" contests (Archer and Huntingford, 1994). However, the presence of combat-induced injuries has likely been underestimated (e.g., Geist, 1986;Huntingford and Turner, 1987;Ham et al, 2021;Grimes et al, 2022), and detailed analyses of actual combat reveals that when the opponent's defenses are breached, a combatant will not hesitate to deliver a potentially injurious attack (Geist, 1965, Geist, 1967Geist, 1971;Pellis et al, 2013). Moreover, if the recipient of an attack successfully wards off the offensive maneuver, it can deliver an offensive attack of its own.…”