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Marine Mammals That Eat Fish

Marine mammals, together with certain large fish and birds, are at the top of the marine food web. The diet of select marine mammals, such as dolphins and porpoises, is made up principally of fish, while that of others, such as polar bears, includes a much smaller percentage of fish. Certain predators of fish, such as the killer whale, which is a member of the dolphin family, represent one of the most noteworthy of ocean hunters.

Killer Whales
- This black and white, toothed whale is a significant ocean predator. The diet of killer whales is varied and also differs from one area to another. Killer whales in Antarctic waters eat a higher percentage of fish than those found in the Bering Sea. Fish makes up 67 percent of the diet of Antarctic killer whales and only 65 percent of the diet of killer whales in the Bering Sea. Resident killer whales also eat a higher percentage of fish than transient killer whales, which prey mainly on other marine mammals, including other killer whales. Killer whales tend to cooperate with each other during a hunt and eat up to 4 percent of their body weight daily.
Dolphins
- Dolphins are powerful marine predators and eat a varied diet, including a variety of fishes. The actual diet of dolphins is dependant on the creature's geographic location. Dolphins hunt in groups known as pods and each individual animal plays a significant role within the group. These fast and sleek marine predators often herd fish into a compact school before swimming through the mass of fish and feeding on them. Dolphins will also chase fish into shallow water, where they can be easily captured. Dolphins also prey on large, non-schooling fish species and frequently stun them by hitting them with their tail flukes. Dolphins swallow fish head first, to prevent spines from lodging in their throat.
Polar Bears
- These white bears are found along coastal areas that border the sea in the Arctic. They are powerful swimmers which can attain speeds of six miles per hour. Polar bears close their nostrils while swimming, but keep their eyes open. Polar bears feed mainly on the fat of seals, but eat fish when other marine mammal prey is not available. The stomach of a polar bear can hold between 15 and 20 percent of its body weight in food. These large and powerful marine mammals can use up to 84 percent of the protein that they feed on.
Harbour Porpoise
- The harbour porpoise is found throughout the temperate and boreal waters of the northern hemisphere. This species prefers coastal waters, but harbour porpoises have been sighted in deep water as well. Harbour porpoises tend to remain in an area for extended periods of time and are generally sighted in small groups of up to three individuals. This porpoise feeds on small schooling fish, including cod, hake, herring, salmon, eelpouts and sandlance.

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