Rate of movement of juvenile lemon sharks in a novel open field, are we measuring activity or reaction to novelty?

Personality differences are widespread throughout the animal kingdom and can have important ecological and evolutionary consequences. Despite a rapidly increasing body of literature, large (marine) vertebrates remain underrepresented in personality research. Given their unique life history traits (e.g. slow growth rate, slow reproduction rate, long life span) and their pivotal role in ecosystem processes, this is an important gap in our current knowledge. Here we investigated consistency and plasticity in movement behaviour of wild juvenile lemon sharks, Negaprion brevirostris, by repeatedly subjecting sharks to open field tests. First, we investigated the presence of interindividual differences in movement behaviour in a novel open field. Second, we investigated the effect of trial repetition on movement behaviour to understand whether movement in a novel open field reflects a reaction to novelty, or general activity. Third, we estimated individual differences in habituation/sensitization rates over trial repetition and studied how the habituation rate was predicted by the initial movement rate. We found consistent individual differences in movement behaviour during the open field tests. Sharks showed habituation in movement behaviour (i.e. decrease) over repeated trials indicating that the movement behaviour during the first trials is a reaction to novelty, and not general activity. Individuals, however, differed in their rate of habituation (i.e. plasticity) and this rate was negatively related to an individual's movement behaviour in the first open field trial. In addition to showing individual differences in consistency and plasticity in juvenile lemon sharks, our study emphasizes the importance of examining the validity of personality tests when adapting them to new species.