Seal vs. Sea Lion: Your Guide to Knowing the Difference

As the world’s largest marine mammal hospital, The Marine Mammal Center cares for an extraordinary number of animals—not just in the number of patients, but also in the variety of species and medical conditions. Seals and sea lions of multiple species are our most rescued animals. They may be orphaned, diseased, injured or entangled in ocean trash.

Seals and sea lions are both pinnipeds, which means they have front and rear flippers. While these sleek, flipper-footed marine mammals may look similar at first glance, they are distinct families of animals with unique characteristics. From how they look and behave in the wild to how we care for patients at our hospital, learn how you can tell the difference between seals and sea lions. Let’s dive in … 

Sea lions and seals can be found all over the world, with different species adapted to live in different climates and habitats. Along 600 miles of California coastline, the Center rescues and cares for animals in the otariid family such as California sea lions, Steller sea lions, northern fur seals and threatened Guadalupe fur seals. Within the phocid family, we rescue true seals including Pacific harbor seals and northern elephant seals.  

On Hawai‘i Island and Maui, we are also the lead responder for endangered Hawaiian monk seals. In fact, we operate the only hospital dedicated to this species, Ke Kai Ola. The Hawaiian monk seal is one of the most endangered seal species in the world, and conservation efforts are critical to their survival. 

Similar to a human hospital, our expert animal care staff and volunteers provide the highest quality health care for our marine mammal patients. Every animal that comes through our hospital doors receives an individualized treatment plan based on their medical and health needs, and in consideration of their species, age and body condition.  

Animals are admitted to our hospital with a range of ailments, and a difference between seals and sea lions is the prevalence of certain diseases. For example, the majority of our patients suffering from leptospirosis, domoic acid toxicosis and cancer are California sea lions. 

In fact, our veterinarians may suspect leptospirosis in a sea lion even before laboratory tests confirm this diagnosis due to some distinctive behavioral symptoms, which include the animal drinking water and folding its flippers over its abdomen. Patients diagnosed with leptospirosis are treated with antibiotics, fluids and other supportive care. 

Many of the physical and behavioral differences between seals and sea lions inform not only how we rehabilitate our patients, but also the research we conduct into marine mammal health and emerging diseases.  

Our research has also shown that nearly 25 percent of adult California sea lions are developing cancer. In order to study this cancer, we collect samples from each patient, fostering greater understanding of what might be causing the alarming cancer occurrence in sea lions—including environmental and genetic factors. 

While there is more to be learned about the complex factors that play into the development of this disease, what we learn from these sea lions contributes to research that could eventually lead to cures for humans. 

Each animal has a story to tell, and we are able to take what we learn from the hundreds of seals and sea lions we rescue each year to gain valuable insight into ocean health. Together, this information helps us better understand how to protect these animals and our shared ocean.

To ensure our patients are physically and mentally prepared to thrive in the wild, the Center incorporates animal enrichment into our care protocols. Our experts design innovative enrichment for specific species, as well as items that are safe for both seals and sea lions. As an educational tool during rehabilitation, enrichment encourages species-typical behaviors while helping our patients develop crucial problem-solving and survival skills. 

As we observe the intricacies of seal and sea lion behaviors, differences in foraging strategies come to light when these animals engage with certain items. For example, when introduced to the “honeycomb” enrichment, a sturdy box covered in holes and stuffed with fish, our patients use a number of unique tactics to get the fish out. 

Pacific harbor seals and northern elephant seals show similar strategies like sticking their noses in the holes, pushing the honeycomb around, swimming on top of it, and flipping it over and around. Harbor seals also use their front flippers to claw and scratch the holes while elephant seals are a little less active. 

But when California sea lions and Steller sea lions interact with the honeycomb, everything moves fast. The sea lions swirl around the honeycomb, seemingly assessing the fish inside and calculating their strategy for getting them out. 

While sea lions also use tactics like poking in their noses and flipping or pushing the honeycomb around the pool, their agility and strength allow them to utilize additional strategies like pushing the box to the bottom of the pool so they can move the fish toward the holes and pull the fish out. 

The differences in how seals and sea lions interact with enrichment are likely due to how these species hunt for food in the wild. For example, while elephant seals feed on bottom-dwelling creatures and may not need to know how to finagle fish out of a rock crevice, sea lions utilize a wider variety of tactics to find and catch food. 

As our experts continue building new pinniped enrichment, designs for sea lions may need to be more complex because they have more foraging strategies in their mental toolbox that should be practiced. 

Now that you know how to recognize seals and sea lions, learn how you can help protect them. Impacts from human activity—such as climate change, plastic pollution and unsustainable fishing—threaten marine ecosystems vital to marine mammal health and our own health. The greatest threats to seals and sea lions are caused by people, but we can also be their greatest champions.  

You see, it’s people like you who make it possible for sick and injured animals to get the critical care they need to be successfully returned to their ocean home. Your contribution goes a long way to help individual patients as well as support scientific research that will help ensure a healthy ocean future for marine mammals and humans alike. 

Give today to help seals and sea lions