The conundrum of counting Steller sea lions

Searching for innovative solutions to count Steller sea lions

ksweeney

March 23, 2017
Katie Sweeney
Biologist

 

The images you’re viewing on Steller Watch are from the remote cameras we placed at the westernmost reaches of the U.S., where Steller sea lions have declined dramatically. The remote cameras along with marking the animals are two research projects that are part of our mission to pinpoint why Steller sea lions in the western half of the Aleutian Islands are not rebounding like they are to the east.

link_ottersurv
The NOAA Twin Otter flying over Yunaska Island to capture image of Steller sea lions.

In addition to Steller Watch, we just launched an effort to develop a program to automate the yearly Steller sea lion population count, our biggest and perhaps most important research project of the year. We partnered with Kaggle to accomplish this. Kaggle connects people to coders who compete to find a solution to big data challenges, saving organizations time and money. The project called NOAA Fisheries Steller Sea Lion Population Count is now live and runs through the end of June. This story was shared by the Alaska Fisheries Science Center if you’d like to read more.

Counting the Steller sea lion population is vital to monitoring the species and staying on top of abundance trends. Each summer, we head to Alaska and gear up for weeks at sea on a research vessel. Summer is best because it’s when Steller sea lions go on land, which biologists call hauling out. During the rest of the year, sea lions spend a lot of time in the open ocean.

So, how do we count? We use a handful of methods depending on the situation.

The summer months are a busy time for Steller sea lions – females give birth, begin rearing their pups and adults breed. Aggressive males stay on land and fast for months to defend their breeding territories. Even non-breeding juveniles and sub-adult males (males that are not yet sexually or socially mature) haul-out with greater consistency during the breeding season. There’s a flurry of activity at sea lion sites and scientists from the Alaska Fisheries Science Center are closely monitoring as much as possible while we count the population.

hexacopterSo, how do we count? We use a handful of methods depending on the situation. At smaller sites with fewer sea lions, we can count on land or by boat, either on the research vessel itself or by launching small skiffs to get a closer look. At large sites, we take aerial images from a plane or an unoccupied aircraft system, or hexacopter drone. During our 2016 survey, we collected over 20,000 aerial images that we counted 29,427 sea lions from, back at the office.

It takes two biologists up to four months to look through those aerial photos. And in those pictures, there are tens of thousands of individual sea lions, and we count and identify the age and sex of each one we count. We hope computer scientists will connect with us on Kaggle to create an innovative algorithm that can recognize sea lions in aerial photos. Automation, or partial automation, would make counting more efficient and give us biologists more time to focus on other important Steller sea lion research studies.

In our next blog, one of our biologists will share what it’s like to conduct aerial surveys in the traditional way, using a small plane.


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.

We’d also like to know what you’d like to hear about. Head to our Talk forum to post a Question for Biologists and your question could be selected for a future blog post!

You are what you eat

The not-so-glamorous way we investigate Steller sea lion diets

lowell

March 15, 2017
Lowell Fritz
Biologist

 

You are what you eat. That’s the basic philosophy behind monitoring the diets of wild animals. In the case of Steller sea lions, we can’t see what they are eating since they feed at-sea, so we have to investigate their diet in other ways. The most common way to find out what Steller sea lions are eating is to — wait for it — collect and analyze their feces. That’s right, we go onshore to sea lions sites, where they have hauled out and pick up after them. Here’s a picture of a group of us ready to collect scat.

landing
Check out that male sea lion on the right! He’s has not quite grown to start competing with larger males for a breeding territory.

Collecting scat is just like cleaning up after your dog, if your dog weighed over 2,000 pounds! We use gallon size bags for samples. A good collection of many scat samples from one site might weigh 60 lbs.

saracollecting
Welcome to the not-so-glamorous world of being a field biologist!

What can we learn about their diet from analyzing their scat? Well, quite a bit. Sea lions can swallow many fish, squid and octopus whole. Fish bones and squid and octopus beaks from their mouth parts, gradually make their way through the sea lion’s digestive tract. We can isolate these hard parts in the scat to identify individual prey species from just a few bones.

In the lab, the scats are washed in sieves and the hard debris left behind is cleaned and studied further under a microscope. Each solid bit is compared to other parts kept in our reference collection of known sea lion prey species.  As you can imagine, it takes a lot of skill and time to make identifications from small fragments.

Aside from cataloging hard parts, we can also analyze prey DNA found in the soft parts of the scat. This technique is especially good at detecting prey that don’t have very many hard parts (invertebrates like squid and octopus), fish that are very large and may not always be consumed whole (like Pacific cod), and fish that have small and fragile bones (like smooth lumpsucker) that may not make it through the digestive track undamaged. But DNA studies are expensive, so, we use this technique to supplement the traditional studies of hard parts, such as a recent description of the late winter diet of sea lions in the Aleutians.

Collecting scat is just like cleaning up after your dog, if your dog weighed over 2,000 pounds!

Steller sea lions target fish that aggregate near the bottom of the ocean or in the middle the water column. While sea lions can dive a lot deeper than humans, they aren’t considered deep divers compared to other marine mammal species. Most of the prey they target live on the continental shelf in waters less than 650 feet deep — that’s still a little deeper than the Space Needle in Seattle is tall.

Steller sea lions in the Aleutian Islands have a diverse diet. In the Aleutians, there are almost 300 species of fish alone, plus dozens of species of squid and octopus. Steller sea lions consume about 50 different species, usually whatever is the most abundant fish in the area.

Here are some of the most common prey items we see in the Aleutian Islands:

Atka mackerel: 

atkamackereAtka mackerel is one of the most abundant yearlong resident fish in the Aleutians Islands, and it also sustains the largest commercial fishery in the region. During the summer, Steller sea lions feed on enough Atka mackerel to make up more than half of their diet.  In winter, the fish make up about a quarter of their diet.

Pacific cod: cod

Like Atka mackerel, Pacific cod are year round residents and since they grow up to 43 inches long and weigh up to 37 pounds they are probably the biggest fish that sea lions eat in the Aleutian Islands. Pacific cod are consumed more often in winter than summer. In winter, Pacific cod make up about one quarter of the sea lion diet.

redirishlordSculpins: 

Sculpins are bottom-dwelling (demersal) fish that are widely distributed on the continental shelf. Steller sea lions eat mostly red Irish lords based on our DNA analyses. They eat sculpins mostly in winter, when they make up about 15 percent of their diet.

Salmon: salmon

Salmon aren’t considered year round residents of the Aleutian Islands. Steller sea lions eat mostly pink and sockeye salmon based on our DNA analyses, and they eat salmon mostly in summer.

Smooth lumpsuckers: 

smoothlumpsuckerThese funny little guys are an enigma. Not much is known about their abundance and distribution, but Steller sea lions eat them far more often in winter (10 percent of their diet), when lumpsuckers aggregate to spawn, than in summer. Lumpsuckers are named for their pelvic fins that have evolved to form an adhesive disk that enables them to latch onto rocks in areas with a lot of current, like the Aleutian Islands.

Squid and octupuses:octopus

Cephalopods are a group of invertebrates that includes both squid and octopus. Based on DNA evidence in scat, we know Steller sea lions more commonly prey on giant Pacific octopus. Cephalopods make up about 10 percent of the sea lion diet in winter.


I have been studying Steller sea lions since 1990 with NOAA Fisheries Alaska Fisheries Science Center in Seattle.  My primary research interests are sea lion population dynamics, demographics, and interactions with commercial fisheries.  I’ve also worked on fish during my career with NOAA, particularly species eaten by sea lions, like Atka mackerel, walleye pollock (you may know them as fish sticks and imitation “krab”), and Pacific cod.   I graduated from Bucknell University (B.A. Biology, 1976) and College of William and Mary (M.S. Marine Science, 1982), and started my science career in 1982 at Rutgers University as a Research Associate.  At Rutgers, I worked at the Haskin Shellfish Research Laboratory in Bivalve, NJ (down the road from Shellpile… you can’t make this up) studying the shells of mollusks living in habitats ranging from freshwater lakes and streams to deep-sea hydrothermal vents. I even had the opportunity to go down in the Alvin submersible!

*Images of Aleutian Island sea lion prey were borrowed from other NOAA Fisheries programs. 

March 1st: ~26

Sea Lion of the Month

Our very first Sea Lion of the Month is ~26! She’s the ‘cover girl’ featured on the About  project page. This sea lion was one of the first to be marked in 2011, when this project began. She weighed 67 pounds and was a little over 3.5 feet long—a very healthy pup!

5c7e489e-9b48-42e3-8ab8-b7dfc36972f6
We have seen her quite often in our remote camera images and in person during our research cruises in 2012, 2013, and in 2015—when we took the picture above.

marchShe seems to be staying local, near her birth place at Gillon Point (star, map left) on Agattu Island. We have also seen her  at Cape Sabak (on the same Agattu Island) and nearby on Alaid Island (circled stars).

We didn’t see her during our summer 2016 research cruise but don’t worry, it seems she can be elusive since we didn’t see her in 2014 either. She would be just over 5 years old which means the next time we see her, she could have a pup. Keep an eye out for her in the images!


If there is a sea lion you keep seeing and would like to know more, head to the Sea Lion of the Month Nomination forum to submit the full marking and we will try to feature that sea lion and share what we know of their story on the first of the month.