Ontogeny of rake mark scarring on common dolphins (Delphinus delphis): insights to aggression and affiliation?

Aggressive and affiliative interactions shape resource allocation, social structure and reproduction in social species. In delphinids, rake marks (parallel scars from tooth raking) indicate social interactions. When examined alongside ontogeny, demographic traits and scar position, rake marks can inform social dynamics. We assessed rake marks on common dolphins (Delphinus delphis) in Aotearoa New Zealand (2006-2024; n = 102) during post-mortem examinations to explore drivers of social behaviour. Using a zero-inflated generalized linear mixed model, we assessed rake mark occurrence (probability of rake density > 0) and prevalence (rake density, rake marks dm-2) across the body (n = 101; dorsal/ventral, cranial/caudal, left/right) in relation to sex, age, total body length (TBL), sexual maturity, body condition (n = 101) and female reproductive status (n = 51), to infer confrontation, avoidance and lateralization. Females showed higher rake mark prevalence but lower occurrence than males, suggesting infrequent but prolonged interactions, possibly sexual coercion. Rake prevalence and occurrence increased with TBL, potentially related to increased social interactions and surface area in larger individuals. Age, sexual maturity, body condition, and female reproductive status were not strong predictors of rake mark occurrence or prevalence. Our findings highlight rake marks as potential indicators of social dynamics.