Seals and sea lions: What’s the difference?

There are a few tricks to tell the difference between these two animal groups


September 13, 2017
Katie Sweeney



Now that we have started seeing reports of northern fur seal sightings from citizen scientists in our remote camera images on Steller Watch, I thought this would be the perfect time to discuss the differences between seals and sea lions! Northern fur seals add a bit confusion as they have “seal” in their name but, are they true seals? The short answer is, “no!”

Pinnipeds can be found in waters all over the world, even some lakes!

Here’s the long answer…

Pinnipeds (or suborder pinnipedia, which means “feather-” or “flipper-footed”) include three different groups of animals: walrus (the Odobenidae family), seals (Phocidae family), and sea lions (Otariidae family). The walrus is the only species alive in the Odobenidae family and can be found throughout the arctic (North Pacific and North Atlantic Oceans). They are one of the largest pinnipeds and actually have air sacks in their chest that they can inflate to help them float, much like a life jacket (reference: Marine Mammal Center)!

Generally accepted classification of the carnivora order. These sorts of classifications can change over time as new fossil and DNA evidence becomes available.

Seals, or ‘phocids’ (sounds like “faux-sids”), are often referred to as true seals or earless seals. They do in fact have ears though no external ear flaps, just small holes on either side of their head. Phocids also have small front flippers and while on land, galumph, or “inchworm”, to move around. At-sea, they use their hind flippers to propel themselves.

This is a great infographic showing different phocid species. Created by Peppermint Narwhal (via Facebook).

Sea lions, or ‘otariids’ (sounds like “oat-a-ry-ids”), are often referred to as eared seals include both sea lions and fur seals. Otariids have external ear flaps and large front flippers that they can rotate around and down in order to stand upright and “walk” on land. At-sea, they mostly use their large front flippers to propel themselves through the water. Fur seals do differ a bit from their fellow sea lion otarrids in that they have longer flippers and thicker fur. So, both northern fur seals and Steller sea lions are otariids and not phocids, or “seals”! Check out the images below of a northern fur seal pup and Steller sea lion pups showing those external ear flaps and upright posture and rotated flippers.

Pinnipeds can be found in waters all over the world, even some lakes! You may notice that there aren’t many species that inhabit warm tropical areas around the equator, though there are a few.

National Geographic infographic of pinniped species worldwide distribution (1987).

We will be sharing more about these northern fur seals in Alaska that many of you may start to see at Cape St. Stephens (Kiska Island) in remote camera images. There is an interesting project happening right now that I will share more about in our next blog post!

I have been a biologist in NOAA Fisheries Alaska Fisheries Science Center studying Steller sea lion population abundance and life history for over 10 years. I am an FAA certified remote pilot and have been flying marine mammal surveys with our hexacopter since 2014. I earned my B.S. in Aquatic and Fishery Sciences at the University of Washington and my Master in Coastal Environmental Management at Duke University. 

The fastest aerial survey of them all!

Check out the blog written by our aerial survey team

Josh Cutler                 Lowell Fritz                   Katie Luxa

Here is the blog from AFSC’s Dispatches from the Field written by this year’s aerial survey team—and featured Steller Watch bloggers—during the 2017 Steller sea lion aerial survey they conducted from June 27th to July 6th.

How Many Steller sea lions are there?

June 21, 2017—It is impossible to know exactly how many Steller sea lions are in the ocean. Luckily, the sea lions converge every summer on shore to give birth, mate, and rear newborn pups. For us researchers, this is a fantastic opportunity to count how many are on shore every year.

However, we must conduct our survey within a three week window. The timing has to be just right to ensure females have given birth. Wait too long and the animals (including newborn pups) will begin to disperse.

On top of the time constraint, we have 2,500 miles of coast to survey, from southeast Alaska through the Aleutian Island chain.


Collecting Information from the air

With the help of NOAA’s Aircraft Operations Center, we fly over the Steller sea lion rookery (where most of the pups are born) and haul-out sites in a Twin Otter plane.

This year we are going to fly over southeast Alaska, Prince William Sound, the Kenai Peninsula, and Kodiak Island. We will start our survey in Sika on June 26 and end near Kodiak on July 10.


Cameras mounted to the belly of the plane take high-resolution images of the sites below. Because it would take more than three weeks to survey all of the beaches, islands, and offshore rocks of Alaska, we alternate between the eastern (southeast Alaska through Kodiak) and western (the western Gulf of Alaska and Aleutian Islands) halves each year.

Technology helps us cover more ground

Our group also uses unmanned aircraft to survey Steller sea lions, primarily in hard-to-reach sites of the Aleutian Islands. This survey is done off the U.S. Fish and Wildlife research vessel M/V Tiĝlâx when we are surveying from the Twin Otter. See this link for more information.

Analyzing collected data

At the end of the survey, two scientists will independently count every sea lion in the 1000’s of high-resolution images that we took.


Counts of Steller sea lions during the breeding season are a consistent proportion of the total population (since some are at-sea when our images are taken). However, when compared across years, these counts allow us to track population trends.

A lot of ground covered in under two weeks

July 14, 2017—The 2017 Steller sea lion aerial survey went by so fast that we did not have a chance to send out an update until it was over! We had nearly perfect weather for flying and aerial photography: low winds, little precipitation, and high clouds. In 2015, this survey took 17 days to complete. We completed the 2017 survey in 10 days. There were only 3 “down days” – days we could not fly due to weather – during the survey period. Over the course of the 7 days in the air, we surveyed 196 sites , took 22,184 photographs, and traveled almost 6000 miles in approximately 40 hours of flight time. This includes 23 bonus sites in the Shumagin Islands, an area we did not plan to survey until the 2018 Aleutian Islands survey. The weather in the Shumagins is often poor and dangerous, so we took advantage of our extra time and unusually good weather to survey the islands this year.


What we saw

We saw sites with 1 or 2 lonely males, and sites with thousands of sea lions packed on a beach. We will know how many sea lions were actually at those sites in the next couple of months after two scientists independently count every sea lion in the images we took.

We even saw some of our marked sea lions from our survey altitude of 750 feet. You can read about the valuable information we learn from marked sea lions, and you can even help us find marks in the western Aleutian Islands at Steller Watch.

September 1st: =34 and =35

Sea Lion of the Month

Many of you have reported sightings of humans at Hasgox Point (Ulak Island) in the newest set of remote camera images hosted on Steller Watch. One of our favorites is the picture of our Steller Watch biologist Katie collecting scat! These images were captured of us during our last fall female capture trip in October of 2015. You can read more about these types of trips in this blog post by biologist Brian Fadely.

This is how you carefully weigh a 800+ Ib (363+ kg) sea lion!

We visited Hasgox Point on October 5, 2015, and darted and captured two adult females: a feat that we had never accomplished before! These captures were conducted one after the other on different parts of this large site — not at the same time — to insure the safety of the animals and our scientific crew. Since seeing this activity, we thought it would be fitting to feature these two adult females as our Sea lions of the Month for September!

The first female we captured was marked as =34. She was the largest female we have ever captured! She weighed about 839 Ibs (380.5 kg), was almost 9 ft (268 cm) long, and measured almost 6 ft (177.5 cm) around her torso (measured just under her front flippers). Based on the wear and tear of her teeth, it seems she was an older female, which could explain her large size.


When we first came upon =34, she was spotted nursing a juvenile. We spotted her at Hasgox Point the following year (2016) during our research cruise. We observed her nursing a juvenile. We’re not sure but this juvenile could be the same that we saw in 2015 (making it a two year old), or it could have been a new pup she had delivered in 2015 that we just didn’t see during our visit. This mystery will hopefully be solved by your observations of the remote camera images! This year, we saw her again at Hasgox Point but we didn’t get a good enough look to see if she had a new pup or juvenile.

Working up an anesthetized adult female sea lion, =35.

The second female that we captured was marked as — you guessed it — =35. Interestingly, this female was the smallest female we have ever captured. She weighed 492 Ibs (223 kg), was almost 8 ft (235 cm) long, and measured almost 5 ft (142 cm) around her torso. Because she was smaller and her teeth weren’t very worn, it’s more likely that she is a younger female. Since we saw her nursing a pup, we can can assume she is no younger than 5 or 6 years old. We didn’t see her in 2016 during our research cruise but hopefully our remote cameras captured images of her! We did see her this year during our visit to Hasgox Point, nursing her new pup!


The main goal of capturing these females was to glue satellite tags onto their heads so we could track their foraging (or feeding) behavior over winter. The satellite tag on =34 transmitted for 227 days (orange trackline in image below, right)! Shortly after her release she headed to Amchitka Island for awhile and in May 2016 made a brief visit to Hasgox Point. She returned to Amchitka Island shortly after where the tag stopped transmitting. Then, we saw her in early July 2016 at Hasgox Point during our research cruise nursing that mystery juvenile.

When we captured =35, she had been actively molting, or shedding her coat of fur. This usually occurs in the early fall which is why we plan our female capture trips in early October, hopefully after molting but before the weather gets worse. Because she was molting, her tag only lasted 16 days. In that time we saw that she stuck around Ulak Island and to the southeast of Ulak (red trackline in image above, right).

Keep an eye out for these two marked females — you’re likely to see glimpses of them and maybe you can tell us what =35 was up to after her tag stopped working!

Curious about other pinnipeds (seals and sea lions)? Check out our neighbors in the Pacific Islands to the south, the monk seals of the Northwest Hawaiian Islands. The Pacific Island Fisheries Science Center features their own Monk Seal of the Month!

We will share the story of one marked sea lion each month. Be sure to check our Sea Lion of the Month page on the 1st of every month to learn about our featured Steller sear lion. You may nominate a sea lion by submitting their full mark on the Sea Lion of the Month nomination forum. Thank you all for your nominations!