Predators and distance between habitat patches modify gap crossing behaviour of juvenile Atlantic cod (Gadus morhua, L. 1758)

When habitat refugia is fragmented and limited, movement of potential prey animals between patches of protective habitat may be driven by biotic factors including foraging opportunities, risk of predation mortality, as well as density effects. However, few studies have examined these factors in marine landscapes. We examined gap crossing behaviour of juvenile Atlantic cod, Gadus morhua L. 1758, a species with high mortality throughout its juvenile stage. We examined the effect of inter-patch distance, fish length, group size, and the presence of a predator on gap crossing behaviour by juvenile cod in a 12 × 3 m experimental arena. Habitat patches consisting of artificial eelgrass were positioned within the arena with inter-patch distances of 3.0 m and 7.5 m. We observed a 37% reduction in frequency of gap crossing movements at larger distances compared to small ones. At the greater inter-patch distance, fish delayed departing a patch, depending on average group size. Juvenile fish released into a patch with a nearby predator moved across gaps 75% less frequently than fish originating in a predator-free patch. We also found that the presence of a predator delayed fish departure from a patch, again depending on group size. Our study demonstrates a suite of complex behavioural mechanisms that juvenile cod may exhibit to reduce predation risk as they navigate a landscape of fragmented habitat patches.

► We studied the movement of juvenile Atlantic cod between two habitat patches.
► We explore the potential effects of inter-patch distance and predator presence.
► Increased inter-patch distance reduces movement frequency as does predator presence.
► Interactive effects influence fish movement between patches.