Nocturnal Haul‐Out Behavior of Rehabilitated Gray Seal Juveniles ( Halichoerus grypus ) in the Baltic Sea

ABSTRACT

Haul‐out behavior is a key component of the behavioral ecology of pinnipeds and serves essential resting functions. Various intrinsic and extrinsic factors have been shown to determine the occurrence of haul‐out events. However, in the Baltic Sea, a nontidal, semi‐enclosed shelf sea, the drivers of haul‐out behavior in seals are not well characterized, especially in juveniles. In this study, 14 rehabilitated juvenile gray seals ( Halichoerus grypus ) were equipped with Argos satellite transmitters to enable post‐release monitoring and to investigate the spatial and temporal aspects of haul‐out behavior. The animals dispersed widely in the Baltic Sea and hauled out along coastal areas that largely overlapped with sites used by wild conspecifics. Seals tended to haul out during evening and night hours, with peak activity occurring after sunset. Both the probability and duration of haul‐out events showed a tendency to increase with longer nights. No seasonal patterns or effects of sex or release year were identified. The association between haul‐out behavior and nighttime suggests a possible link to prey activity patterns but does not preclude additional factors such as physiological rhythms, potential effects of rehabilitation, or inherited behavioral tendencies shaped by historical hunting pressure. Our findings indicate that such patterns may emerge early in life, independent of prior experience.