The Harp Seal (Pagophilus groenlandicus) is a marine carnivore inhabiting the cold waters of the North Atlantic and Arctic Oceans. These seals undertake extensive migrations, driven by the pursuit of food and suitable breeding conditions. Their ability to thrive in a harsh, variable environment stems from a highly adaptable, opportunistic diet that capitalizes on seasonal and regional prey availability. Understanding the Harp Seal’s feeding habits requires examining the wide variety of fish and invertebrates it consumes, along with the behavioral and environmental factors that shape its foraging strategy. The specifics of its diet reflect its position as a major predator in the dynamic Arctic and Subarctic food webs.
The Core Diet: Fish, Crustaceans, and Other Prey
The diet of an adult Harp Seal is dominated by fish, but they consume a remarkably wide array of prey. The most significant staple species is the Capelin, a small schooling fish that is energy-rich and often forms dense, localized populations. Other frequently consumed fish include:
- Arctic Cod
- Polar Cod
- Herring
- Sand Lance
- Greenland Halibut
- Redfish
- Plaice
Crustaceans form a substantial part of the seal’s diet, especially for younger individuals and during certain seasons. These invertebrates include small, fat-rich organisms like Euphausiids (krill) and various species of pelagic amphipods, such as Themisto libellula. Decapods, including shrimp and prawns, are also consumed, providing a reliable source of protein and fat. The consumption of crustaceans is particularly important in northern feeding grounds and for seals that are still developing their hunting skills.
Harp Seals are opportunistic feeders. While fish and crustaceans make up the majority of their intake, they occasionally consume other marine life. Cephalopods, such as squid, are a secondary food source taken when locally abundant. The seals’ diet is ultimately a reflection of which organisms are most accessible and energy-dense in their immediate foraging area.
Foraging Behavior and Seasonal Dietary Changes
Harp Seals are accomplished divers, using their specialized physiology to hunt prey throughout the water column. They routinely dive to depths of 100 to 200 meters, but they are capable of reaching depths of over 400 meters and can remain submerged for up to 16 minutes. When hunting smaller fish like Capelin, the seals often swallow their prey whole underwater, only bringing larger catches to the surface for consumption.
The seals’ diving behavior changes significantly between age groups, which influences their early diet. Juvenile seals initially perform much shallower and shorter dives, averaging around 40 meters for 2.5 minutes. This limited capability forces weaned pups to rely on smaller, slower-moving pelagic crustaceans like krill and amphipods until their diving physiology and skill improve.
Dietary shifts are pronounced throughout the year, driven by the seals’ massive annual migration and corresponding biological events. Following the high-energy demands of breeding and molting in spring, the seals feed intensely through the summer and autumn, targeting lipid-rich prey to build up blubber reserves. For example, in the Barents Sea, their late summer diet often consists mainly of krill and Polar Cod, switching to a more fish-centric diet of Capelin and Herring as they migrate south during winter. This strategic feeding ensures they have the energy stores necessary to sustain them through periods of fasting.
The Influence of Arctic and Subarctic Habitats
The existence of three distinct Harp Seal populations—in the Northwest Atlantic, the Greenland Sea, and the White Sea—is directly linked to the availability and movement of their prey. Their annual cycle involves extensive north-south migrations that can cover over 5,000 kilometers, dictated primarily by the distribution of schooling fish like Capelin and the formation of sea ice. The seals follow the ice edge, which often concentrates prey and provides a reliable platform for resting and birthing.
Sea ice is a prerequisite for reproduction, as it provides a stable platform for birthing and nursing pups. Its presence strongly influences where seals must forage nearby. The location of the ice edge during the feeding season is also where prey species like krill and Capelin are often most abundant, creating localized feeding hotspots. This dependency means that the seals’ access to food is tied to the health and extent of the ice habitat.
As a major predator, the Harp Seal plays a significant role in the food web dynamics of the North Atlantic, consuming large volumes of fish and invertebrates annually. Changes in ocean temperature and circulation patterns, often linked to climate change, can dramatically affect the distribution and abundance of their prey, particularly ice-dependent species like Capelin. Shifts in these fish stocks force the seals to alter their foraging patterns, sometimes leading to longer migrations or a reliance on less energy-dense food sources. This sensitivity to environmental changes makes the Harp Seal an indicator species for monitoring the overall stability of the Arctic marine ecosystem.