Seals, marine mammals belonging to the group called pinnipeds, exhibit activity patterns that vary significantly across species. The timing of their most active periods depends on a complex interplay of environmental factors, such as light and tides, and biological necessities, including foraging and their annual reproductive cycle. Understanding when seals are most engaged requires looking at both their daily routines and the major seasonal events that dictate their yearly energy expenditure.
Daily Cycles: Foraging and Feeding Times
A seal’s daily activity is primarily driven by the need to forage and is often synchronized with the movements of their prey. Many seal species are nocturnal or crepuscular hunters, meaning they are most active during the night or twilight hours around dawn and dusk. This pattern is directly linked to diel vertical migration (DVM).
During DVM, small fish and invertebrates, the seals’ primary food source, ascend from deeper waters to the surface layers to feed under the cover of darkness. This vertical movement makes the prey more accessible to seals at night, allowing them to expend less energy on deep dives. For example, the Weddell seal in the Antarctic shifts its diving behavior from nocturnal during the summer to diurnal for the rest of the year, reflecting changes in prey availability under the extreme light regimes of the poles.
The light intensity in the water column acts as the primary cue for this daily migration, and seals exploit the resulting concentration of prey near the surface. Conversely, some seals, like the Baltic grey seal, exhibit more focused foraging dives during midday. This suggests a species-specific variation in feeding strategy, perhaps targeting less migratory prey or capitalizing on different local conditions.
The time a seal spends at sea foraging can vary dramatically, ranging from short trips of a few hours to multi-day excursions. An individual seal must balance the energetic cost of a hunt against the potential caloric return. The specific timing of feeding is a dynamic decision influenced by local prey distribution, water clarity, and the presence of aquatic predators.
Seasonal Peak Activity Periods
The highest levels of energy expenditure and most intense activity for seals occur during their annual reproductive and molting cycles. These seasonal peaks demand maximum output, often involving long periods without feeding and intense social interaction. The breeding and mating season is one of the most active times, with males engaging in fierce competition to secure access to females.
Male grey seals, for example, arrive at traditional breeding sites, called rookeries, ahead of the females to establish and defend territories. This intense social activity and territorial defense can lead to noisy clashes as they compete for a harem of up to ten females. For the females, the pupping season immediately preceding mating is the most demanding time, requiring high activity for nursing and protecting their young.
The timing of pupping is species-specific and geographically variable. Common seals typically give birth in late spring or early summer, while grey seals in the UK generally pup from late August into January. During this period, mother seals are highly active, making frequent foraging trips while rapidly building up their pup’s blubber reserves.
Following the pupping and mating season, many seals undertake long-distance migrations to reach optimal feeding grounds. Grey seals, for instance, travel over 100 kilometers on foraging trips, representing a massive energy output. This movement ensures they can recover the energy lost during the breeding season.
Hauling Out and Rest Periods
When seals are not actively foraging or engaged in seasonal life events, they spend time hauling out, which means leaving the water to rest on land or ice. Hauling out is a critical part of their daily routine and represents a period of reduced activity. The timing of this rest is influenced by several external factors.
One primary reason for hauling out is thermoregulation, as seals use the land or ice to warm up or cool down. It is also important for predator avoidance, as being ashore removes the threat from aquatic predators like orcas or large sharks. Molting, the annual shedding of their fur, is another significant trigger, as remaining hauled out elevates skin temperature and helps speed up hair and skin regrowth.
For many coastal species, the most consistent factor influencing hauling out is the tidal cycle. Harbor seals, for example, often choose to haul out on exposed sandbars or rocks during low tide, which provides easier access and a safer distance from terrestrial disturbances. Peak counts of hauled-out seals often center on low tides that occur during the middle of the day, maximizing rest and minimizing travel energy.
The amount of time seals spend hauled out also varies seasonally, with peak numbers observed during the molting period in late summer. Although they may appear inactive, the decision to haul out and the duration of their stay are carefully timed behaviors necessary for maintaining overall health and energy balance.