Otters are semi-aquatic mammals belonging to the Mustelidae family, which also includes weasels and badgers. These animals spend a significant portion of their lives hunting in freshwater and marine environments. Their reliance on aquatic habitats raises questions about their food sources, particularly whether they incorporate vegetation into their daily intake.
Otters Are Not Herbivores
Otters are definitively classified as carnivores, meaning their diet consists almost entirely of animal matter. Their biological order, Carnivora, reflects a physiology adapted to consume and process meat, not plants. This classification applies to all 13 existing species, from the smallest Asian small-clawed otter to the largest giant otter.
While they may occasionally ingest small amounts of plant material, such as aquatic vegetation, roots, or berries, this consumption is accidental or incidental. Plant matter is typically consumed only when accidentally swallowed with prey or when other food sources are scarce. The energy derived from these occasional plants is insignificant to their overall sustenance.
The Staple Otter Diet
The energy otters require to maintain their high metabolism comes from aquatic prey. The specific composition of an otter’s diet varies significantly based on species, habitat, and local food availability. This varied hunting strategy ensures they secure the substantial amount of protein needed to survive.
River Otters
River otters, such as the North American species, are generalist carnivores that primarily consume fish. They are opportunistic hunters and also prey on crayfish, crabs, and amphibians like frogs. They will also hunt birds, their eggs, and small terrestrial mammals when available.
Sea Otters
Sea otters have a diet specialized for the marine environment, focusing heavily on marine invertebrates. Their preference includes sea urchins, abalones, clams, mussels, and crabs. These specialists are known for using rocks as tools to crack open the hard shells of their prey.
Digestive System Adaptation
The otter’s anatomy provides the clearest evidence of its carnivorous nature, particularly in its specialized digestive system. Like all true carnivores, otters possess a relatively short and simple alimentary canal. This short gut is highly efficient at processing protein and fat, which are quickly broken down and absorbed.
The short length of the digestive tract is poorly suited for the complex task of breaking down cellulose and other structural carbohydrates found in plant cell walls. Herbivores and omnivores require much longer guts, often with specialized chambers, to extract nutrients from vegetation. For a river otter, food can pass through the entire system in as little as one to four hours.
Their dentition is also specifically adapted for a meat-heavy diet. Otters possess sharp canine teeth for gripping slippery prey and specialized cheek teeth, known as carnassials, for shearing flesh. Even the wide molars of the sea otter, which are built for crushing the hard shells of mollusks, are optimized for processing animal tissue rather than grinding fibrous plant material.