Otters are semi-aquatic mammals belonging to the Mustelidae family, which also includes weasels and badgers. Otters are classified as carnivores, meaning their specialized digestive systems are designed to process animal matter. Their diet consists almost entirely of the meat of other creatures, a predatory nature characteristic of all 13 recognized otter species.
The Primary Aquatic Prey
The vast majority of an otter’s food intake comes from aquatic sources, making them skilled hunters in rivers, lakes, and coastal areas. Fish constitute the staple of the diet for most otter species, providing necessary protein and fat content. Otters are adept at catching a variety of fish, often preferring slower-moving species.
Crustaceans, particularly crayfish, crabs, and shrimp, form a significant part of their carnivorous menu. The availability of these invertebrates often dictates local feeding habits and seasonal shifts in the diet. Amphibians, such as frogs, are also regularly hunted in freshwater environments. Occasionally, otters opportunistically hunt small reptiles, insects, or even ground-nesting birds and their eggs.
Specialized Diets of Key Species
River Otters
While all otters are carnivores, the exact composition of their diet varies dramatically between species and environments. River otters, such as the North American river otter, are generalist carnivores. They rely heavily on the fish and amphibians readily available in freshwater systems. Their powerful swimming and agility allow them to pursue prey like trout and suckers in rapid currents.
Sea Otters
In contrast, the Sea Otter has developed a highly specialized diet tailored to its marine environment, focusing on hard-shelled invertebrates. These otters routinely consume sea urchins, clams, mussels, and abalone. Accessing the soft meat inside requires specific techniques; the Sea Otter is one of the few mammals known to use tools, often employing rocks to break open tough shells. Marine otters prioritize high-calorie shellfish over the fish that dominate the menu of their river-dwelling relatives.
High Energy Demands
The otter’s predatory lifestyle is driven by the necessity of maintaining a high core body temperature in cold water. They do not possess a layer of insulating blubber like many other marine mammals. Instead, they rely on incredibly dense fur and a high metabolic rate. This metabolic demand is approximately two to three times higher than that of a similarly sized terrestrial mammal.
To sustain this elevated metabolism, an otter must consume a remarkable volume of food every day. Most otters, especially sea otters, need to eat between 15% and 25% of their total body weight daily just to survive. This high-volume consumption explains why they spend a significant portion of their day actively hunting and feeding. Their need for a continuous supply of meat dictates their behavior and ecological role as aquatic predators.