Harbor seals are common marine mammals found along temperate coastal regions of North America, Europe, and Asia. As opportunistic predators, they adapt their diet based on available food. These seals play a role in coastal marine ecosystems, feeding primarily on marine and estuarine animals. They can also be found in rivers and freshwater lakes, adapting their foraging to these diverse habitats.
Primary Prey
The diet of harbor seals is diverse, consisting mainly of fish, shellfish, and crustaceans. They consume a variety of fish species, including rockfish, herring, flounder, salmon, hake, and sand lance. Beyond fish, harbor seals also prey on invertebrates like squid and octopus.
Their diet varies significantly depending on the season and geographical location. For instance, in Alaskan waters, their diet frequently includes walleye pollock, Pacific cod, capelin, eulachin, Pacific herring, Pacific salmon, sculpin, and various flatfish. Studies in the Salish Sea have identified Pacific Herring, Pacific Sand Lance, and Northern Anchovy as significant portions of their diet, with salmonids and herring being particularly important for biomass consumed.
Foraging Behavior
Harbor seals are adept hunters, utilizing both shallow and deep dives to capture prey. They can remain submerged for extended periods, even sleeping underwater and surfacing for air approximately every 30 minutes. Harbor seals typically swallow prey whole or tear it into smaller chunks. However, they possess strong back molars to crush the shells of crustaceans and mollusks.
When hunting in dark or murky conditions, harbor seals rely on their sensitive whiskers, known as vibrissae, to detect prey. These whiskers sense vibrations in the water, helping seals locate food even when visibility is poor. While they often forage alone, their hunting behavior can also be influenced by factors like specific haul-out locations.
Dietary Influences
Several factors influence the diet of harbor seals, highlighting their adaptability. Environmental elements, such as their habitat (estuaries, open coasts, rivers, or lakes), play a role in determining prey availability. The seasonal abundance of certain prey species also dictates what seals consume. Geographical location causes regional variations in their diet, as different marine ecosystems offer different food sources.
Biological factors also contribute to dietary variations. A seal’s age, size, and reproductive status can influence its energy needs and, consequently, its food choices. For example, studies indicate that diet can vary between males and females, and between breeding and non-breeding individuals. This adaptability ensures harbor seals maintain their energy intake across different life stages and environmental conditions, consuming approximately 5-6% of their body weight, or about 4.5-8.2 kg (10-18 lb.), each day.