Seals are fascinating marine mammals that live all over the world. If you’ve ever seen them balancing balls on their noses or clapping their flippers, you may have wondered – what do seals eat? Are seals herbivores that only eat plants or do they eat other things too?
If you’re short on time, here’s a quick answer: Seals are carnivores that mostly eat fish, squid, crustaceans, and sometimes birds or other small marine mammals to survive. They are not herbivores.
In this approximately 3000 word article, we’ll take an in-depth look at the diets of different seal species. We’ll cover what seals eat, how much they eat per day, how they hunt and catch their prey, how their teeth and digestive systems are adapted for eating meat, and compare their nutrient requirements to those of herbivorous animals.
An Overview of Seal Classification and Species
Pinnipeds and Seal Taxonomy
Seals belong to a group of marine mammals called pinnipeds, which also includes sea lions and walruses. Pinnipeds are further divided into three families:
- Otariidae – the eared seals, including sea lions and fur seals
- Odobenidae – the walrus
- Phocidae – the earless seals, or true seals
There are 33 species of true seals, including harbor seals, leopard seals, and elephant seals. True seals are well adapted to their marine environment with streamlined bodies, flippers, and external ear flaps.
Key Seal Species and Where They Live
Some of the major true seal species and their geographic ranges include:
- Harbor Seal – found in coastal waters of the northern Atlantic and Pacific Oceans
- Gray Seal – found in coastal waters of the northern Atlantic Ocean, Baltic Sea, and Sea of Okhotsk
- Harp Seal – found in the northern Atlantic Ocean and Arctic Ocean
- Ringed Seal – found in the Arctic Ocean and some northern Atlantic and Pacific Oceans
- Leopard Seal – found around Antarctica
- Weddell Seal – found in Antarctica
- Mediterranean Monk Seal – found in the Mediterranean Sea
- Hawaiian Monk Seal – found in Hawaii
- Southern Elephant Seal – found in coastal areas around Antarctica
- Northern Elephant Seal – found in coastal areas of the eastern Pacific Ocean
Seals live everywhere from tropical climates to polar regions. Some species, like the harbor seal, have adapted to live in both open ocean and coastal habitats. Species like the leopard seal and elephant seal live exclusively in polar regions around Antarctica.
Seal Diets – What Do Seals Eat?
Fish
Piscivorous seals like fur seals, sea lions, and gray seals primarily feed on fish, which make up 50-80% of their diet. Some commonly eaten fish include cod, hake, herring, capelin, sand lance, and Arctic cod. Their fish consumption varies by location, season, and seal species.
For instance, Antarctic fur seals at South Georgia eat mostly lanternfish and squid in the winter but switch to Antarctic krill in the summer. Pinnipeds locate prey with their exceptional eyesight and hearing before using their speed and agility to capture fish.
Cephalopods
Cephalopods like squid, octopuses, and cuttlefish are another key component of seals’ diets. The importance of cephalopods varies across seal species, comprising over half the diet of elephant seals but only 5-10% for ringed seals.
Seals especially target cephalopods in areas of upwelling where nutrient-rich water supports abundant squid populations. their flexible bodies allow them to access hard-to-reach crevices where cephalopods hide.
Crustaceans
Some phocid seals like harp, ringed, and bearded seals consume a considerable proportion of crustaceans, especially krill and amphipods. For example, a study in Antarctica found that 85% of crabeater seals’ diet consisted of Antarctic krill.
These small shrimp-like crustaceans form vast swarms during the productive summer months. Seals locate and prey on krill patches using their exceptional long-distance vision. Some species also eat larger crustaceans like lobsters, shrimps, isopods, barnacles, and crabs.
Birds and Other Prey
While fish, cephalopods, and crustaceans make up the majority of seals’ diets, they exhibit some opportunistic feeding behavior on other prey like sea birds, arctic terrestrial animals, and even marine mammals.
Leopard seals are most notorious for such predation, feeding on penguins and even small seal pups. Other species like elephant seals may occasionally scavenge dead sea birds or even whales. However, seals derive little overall nutritional value from such episodic predation events.
Seal Hunting and Feeding Behaviors
Foraging and Hunting Techniques
Seals employ various foraging and hunting techniques to catch their prey. They primarily feed on fish, crustaceans, and cephalopods. When hunting, seals rely on their excellent underwater vision and vibrissae (whiskers) to locate prey.
Some species, like leopard seals, are pursuit predators that chase down agile prey like penguins and other seals. Other types, like elephant seals, are ambush predators that hide and explode out to grab passing fish and squid.
Seals have also been observed using coordinated hunting strategies, working together to herd fish into bait balls for easy feeding.
Seals locate prey patches by sensing vibrations, smells, and electrical fields. They can dive over 1,000 meters deep and remain submerged for over an hour in search of food. Their flexible bodies allow for rapid bursts of speed to capture prey.
Seal teeth are adapted for holding onto slippery fish and squid, making it easy to gulp down food under the waves. Some species have developed specialized feeding behaviors, like the gray seal which often sucks the calories rich livers out of fish and leaves the rest behind.
Daily Food Intake Requirements
The daily caloric requirements of seals varies greatly by species, age, sex and whether they are nursing pups. For example, a mature elephant seal bull needs nearly 10% of its body weight in prey daily, about 27 kg, when fueling up for breeding season.
In contrast, a harbor seal only requires 5-8 kg of fish and squid each day to meet its energy needs.
Nursing seal pups have exceptionally high daily feeding requirements. For instance, a baby grey seal pup consumes nearly 10 liters of its mother’s fat rich milk per day while nursing. This allows the pup to quadruple its body weight before being weaned.
After weaning, young seals must intensify their foraging efforts to continue meeting their high caloric needs for development and growth. Their daily food intake gradually decreases as they near full adult size.
Seal Digestive Systems and Dentition for Eating Meat
Stomach Compartments and Intestines
Seals have a multi-chambered stomach and long intestines adapted for digesting meat and fish. Their stomach has 3-4 compartments that allow for thorough breakdown of protein-rich foods. The first compartment, called the cardiac stomach, stores and pre-digests the food.
The next compartments, the fundic and pyloric stomachs, further digest and absorb nutrients. Seals have long small intestines, around 3-5 times their body length, which allows for full absorption of fats and proteins. This intestinal length is similar to other carnivorous mammals like dogs and cats.
The seal’s gastrointestinal system is designed for efficiently utilizing energy from fatty marine animals like fish, squid, and octopus.
Seal Teeth for Gripping Slippery Prey
Seals have sharp teeth ideal for snatching slippery fish and aquatic prey. Their molars interlock to allow gripping and tearing flesh. The teeth near the front are pointed for spearing, while rear teeth are blade-like for shearing meat.
Seals swallow food whole or in large chunks, so they don’t need extensive chewing teeth. Instead, their teeth function for grasping wiggling prey in the water. For example, leopard seals have long fang-like canines for snagging penguins and other prey.
In contrast, crabeater seals have elaborate, dense post-canine teeth forming a sieve for filtering krill out of the water. Other seals like fur seals have pointed molars curving backwards to catch prey and prevent escape.
A seal’s teeth represent its unique hunting style and favored prey in the marine environment.
Nutrient Needs of Seals vs. Herbivores
Macronutrients for Carnivores
As carnivores, seals have high protein requirements to support their muscle mass and active lifestyles. The main macronutrients seals need are protein, fat, and minimal carbohydrates. Their diets are high in protein from fish, providing amino acids for building and repairing tissues.
Seals also need dietary fats for energy, insulation from cold temperatures, and forming cell membranes. Compared to herbivores, seals require almost no carbohydrates since they get ample glucose from protein through gluconeogenesis.
Vitamins and Minerals
The fish-based diet of seals supplies abundant vitamins and minerals like vitamins A, D, B12, iron, selenium, and zinc. Vitamin A supports vision, bone growth, immunity and reproduction. Vitamin D aids calcium absorption and bone health, important for growing seal pups.
Iron carries oxygen through the bloodstream to muscles during dives. Zinc assists with wound healing, immunity, and enzyme function. Unlike strict herbivores, seals easily meet their vitamin and mineral needs from nutrient-dense animal foods without gut fermentation.
In comparison to vegetarian animals, seals are well equipped as carnivores to utilize high protein foods. Their streamlined vitamin and mineral intake echoes their simple digestive system, allowing seals to thrive on a strictly meat-based diet.
Conclusion
In conclusion, seals are clearly well-adapted predators and carnivores, not herbivores. Their diets mainly consist of meat from fish, squid, crustaceans, and sometimes sea birds. Seals have sharp teeth for catching slippery animals and digestive systems tailored to processing high-protein foods, not plant material.
They hunt using their speed and stealth in the water to surprise prey. While some seals may occasionally eat algae or aquatic plants, they cannot survive healthily without large quantities of meat in their diets every day.
Their nutritional needs for protein, vitamins, minerals, and fats are very different from grazing herbivores. So next time you see seals at the aquarium or in wildlife shows, keep in mind – these are powerful marine hunters and meat-eaters through and through!
