Atlantic cod individual spatial behaviour and stable isotope associations in a no-take marine reserve

Foraging is a behavioural process and, therefore, individual behaviour and
diet are theorized to covary. However, few comparisons of individual
behaviour type and diet exist in the wild. We tested whether behaviour
type and diet covary in a protected population of Atlantic cod, Gadus
morhua.  Working in a no-take marine reserve, we could collect
data on natural behavioural variation and diet choice with minimal
anthropogenic disturbance. We inferred behaviour using acoustic telemetry
and diet from stable isotope compositions (expressed as δ13C and δ15N
values). We further investigated whether behaviour and diet could have
survival costs. We found cod with shorter diel vertical migration
distances fed at higher trophic levels. Cod δ13C and δ15N values scaled
positively with body size. Neither behaviour nor diet predicted survival,
indicating phenotypic diversity is maintained without survival costs for
cod in a protected ecosystem. The links between diet and diel vertical
migration highlight that future work is needed to understand whether the
shifts in this behaviour during environmental change (e.g. fishing or
climate), could lead to trophic cascades.