Animal personality (consistent inter-individual behavioural differences) is a focus of ecological and evolutionary researchers due to its influence on individual fitness, and therefore the evolution of a species. Strong, single gene associations with personality traits occur, such as the dopamine receptor gene, DRD4, which has been associated with the bold-shy personality trait. Typical of otariids, the New Zealand sea lion (Phocarctos hookeri) breeds polygynously in high-density breeding colonies. Males physically compete for access to the breeding harem, resulting in a strong male reproductive success skew. Male size is thought to explain differences in male breeding success, but observations of similarly-sized adult males within and outside of the breeding harem suggest that size alone may not adequately explain male reproductive success. Here we propose that animal personality plays an important role in harem access and hence, male reproductive success. We hypothesize that if personality traits influence reproductive success, selection will act upon these traits to produce consistent genetic differences at personality-associated genes, and these genetic differences will be associated with a male’s reproductive success. We screened genetic variation at personality-associated candidate genes (DRD4) in male NZ sea lions at the Sandy Bay breeding colony on the NZ subAntarctic Aucklands Islands. Using a proxy for male personality (male access to the harem, which assumes males that access the harem are bolder personality types), we examined the association between male personality and genetic variants at the candidate genes. Our study will provide insight into the factors that influence reproductive success in otariids.