Animal personalities and their degree of plasticity have been demonstrated to be adaptive and associated with ecologically important traits. While the concept is well established in a broad range of species, studies with free-ranging pinnipeds remain rare. Here we use a long-studied but declining population of Galápagos sea lions to demonstrate the existence of behavioural axes related to boldness in pups with respect to intrinsic and maternal traits. These sea lions reside in a habitat characterized by unpredictable environmental perturbations, which may select for differences in personality between individuals. We tested individual pups during two reproductive seasons (2017 and 2018) and elicited diverse yet repeatable responses to a novel object, which were associated with sex and age but not body mass differences. Responses to novel object and human approach tests were positively associated: pups that approached a novel object were also more likely to stay near humans. Maternal age and body size also affected variation in pups’ responses, suggesting that fitness-relevant characteristics of mothers may influence pup personality. To determine how traits changed across time and contexts, we repeated the novel object test 1 year later in pups born in 2017 and with their mother present during both years. These traits remained repeatable and stable within the first year of life; however, shy pups showed plasticity by increasing their tendency to approach when with mothers, potentially due to maternal social support. We propose that personality in this species is likely to be relevant for coping strategies during later life history events within a changing environment.