An Elephant Seal's Maiden VoyageMarch 1 2018
Elephant seal pups begin their first migration in the Pacific Ocean, learning to navigate and dive without any parental instruction. How do pups find their way home in a seemingly featureless ocean with no map or compass?
By gluing trackers to seal pups, we will learn how they navigate and dive during their first ocean exploration.
This week, I have the privilege of attending 2018 SACNAS: The National Diversity in STEM Conference in San Antonio, Texas to present our project on northern elephant seal tracking!
We wanted to know how accurate light-level geolocation tags are in comparison to ARGOS satellite tags. ARGOS satellite tags are known as the gold standard for animal tracking because of their high levels of accuracy; however, they cost about 3-10x more than geolocation tags. These geolocation tags use light levels to estimate geographic location instead of common methods like GPS and ARGOS. But because these tags rely on light level data, it’s very difficult to use them on animals like elephant seals because they often dive to very dark ocean depths.
As part of the long-term monitoring effort by Dan Costa and the researchers in his lab, 238 female northern elephant seals have been instrumented with both ARGOS and geolocation tags. For my project, we worked on a method that uses day and night patterns to show where each seal was throughout the trip. We found that the geolocation track was within 280 km (2.29º latitude and 1.01º longitude) of the ARGOS track. This means light-level geolocation can be used to track long-ranging and deep-diving animals like elephant seals! This is exciting because we can use light-level geolocation to track animals for a portion of the cost and size of a satellite tag—meaning more animals can now be studied and more questions can be answered.
Using this method, we’ll figure out where the weanlings went during their first trip at sea!
Thanks for tagging along on our adventure!
Take a look at how we mark individual seals! These hair dye marks help us keep track of individual seals.
While the seal pups are out at sea, we are working hard on some other exciting research projects! Last week Diana presented her summer internship project at the UC Santa Cruz Summer Research Symposium. Diana wanted to find out whether drone photos can be used to estimate body mass of elephant seals. She traced the outlines of 14 adult female seals in drone photos and compared those “footprint” measurements to the seals’ measured masses. She found a strong relationship between actual mass and mass measured from drone images – the average error was only 5% of body mass. It looks like drone images can be used to estimate body mass of adult female elephant seals! This is exciting for us because it means we can estimate mass without disturbing animals or carrying around heavy weighing equipment. Great job, Diana!
See photos below for Diana presenting her poster (right) and censusing sea lions on Año Nuevo Island (left).
Meet seal E352, a third elephant seal pup out on her very first migration! She was born in late January 2018 at Año Nuevo State Park and was first seen without her mom on February 28th, 2018.
Her mom, seal GU256, was born in February 2007 and has been seen a total of 98 times since then! She is 11 years old now and was last measured to beat 289 cm long (which is about 9.5 feet!) long and weighed to be 449 kg-- that’s about 990 pounds!
In 2013, researchers wanted to study this seal mom’s migration and tagged her with a time-depth recorder (also called a TDR), a satellite tag and a jaw accelerometer tag. TDR tags help us find out when and how deep a seal dives, whereas and satellite tags show us where she went during her migration. A jaw accelerometer is a small tag that goes right under the chin and measures jaw motion-- this can help us figure out when and where GU256 feeds and what she’s feeding on! You can check out our previous posts for actual TDR dive data and satellite tracks from other seal moms, GT19 and X58!
Have you ever wondered what it might be like to dive and feed in the ocean? Deep dive with U256 and explore where she went in 2013 with this fun 3D dive track! If you look closely in each picture below, you can see some of her individual dives throughout her migration!
Last week, we had the opportunity to visit Año Nuevo Island. Located just 1/2 a mile from the mainland, the Island is not accessible to members of the public - it has been set aside as dedicated wildlife habitat (no one has lived there for over 70 years!). There are about 100 elephant seals and 10,000 sea lions on the Island right now, along with thousands of birds. Landing the boat on the Island is sort of like stepping foot in a modern day Jurassic Park - it's wild and exciting! We spent the day looking for individually marked/tagged sea lions and, of course, keeping an eye out for the weanling seals with trackers. Take a look at the video below to see what it's like to be a researcher out at Año Nuevo!
Want us to make more videos like this? Write a comment and let us know what you'd like to see!
Meet seal D540, another seal pup out on her first migration! If you look really closely at the image below, you can see the dye mark “D540” on her left side, just below her trackers. She was born in mid-January 2018 at Año Nuevo State Park and officially became a weanling when she was first seen without her mom on February 17th, 2018.
Her mom, seal GT19, was born in 2005 and is about 13 years old now! GT19 has been seen almost every year since 2005 and has had six pups in her lifetime-- D540 is her newest pup! This seal mom has been tracked a total of three times to study her migration and dive patterns—once in 2011 and twice in 2016. Check out a day of her diving from 2011 in the image below! The top of the image is the ocean surface, so you can see that she regularly dives down to 500 meters underwater. On that day, she did a total of 68 dives going as deep as 764 meters (that’s 2,507 feet!). To do this, GT19 had to hold her breath for 15-37 minutes each dive! How long can you hold your breath? If you’ve ever tried exercising while holding your breath, you know it’s quite challenging. Seals are experts at exercising while holding their breath!
If you look at the dive image, do you notice that mom GT19 dived shallower at night than during the day? This is called a diel vertical migration, where zooplankton move deeper in the water column during the day so their visual predators (like seals) can’t see them as easily when the sun is out. At night, the zooplankton move shallower in the water column to feed on phytoplankton that are near the ocean surface. When zooplankton move up, the fish follow the zooplankton and seals follow the fish! These elephant seals can help us learn so much about the ocean environment! We wonder if seal pup D540 will dive as deep as her mom during her first year at sea. Hopefully she will return soon so we can find out!
Remember seal D521, our weanling from the last post? Check out where her mother, seal X58, was feeding on this day in 2015 (red flag in image below)! How do we know where she was? In 2015, our researchers glued a satellite tag to the fur on her back in order to study her migration.
Did you know that northern elephant seals have one of the longest independent migrations (not following mom or dad, no group travel) of any mammal? They have two migrations per year and can travel 7,000 miles into the ocean! Northern elephant seals spend about 8 months of the year out at sea foraging for food and only return to land twice per year—once to breed and give birth, and once to molt (shed their skin and fur).
This seal mom, X58, was a weanling back in 2010, and she has been observed every year since—a total of 171 times! She is about 8 years old now and has had four pups, including our weanling D521. We can’t wait to find out if her migration path is similar to D521!
Meet the (animal) team
We’ve deployed our first set of instruments! World, meet seal D521, one of the pups out at sea right now on her first migration! She was born on February 1st 2018 right here at Año Nuevo State Park. At 5 weeks old, she already weighed 132 kilograms (which is about 290 pounds!) and was 164 centimeters from head to tail – that’s 5 feet 5 inches! Is this 5-week-old pup taller than you?
D521 was seen with her mom a total of 12 times from February 5th until March 1st, when she was first observed without her mom (officially weaned, so we can call her a “weanling”!). On March 20th, we found D521 on the beach and quickly glued our tracking devices to the fur on her back. In the picture below, you can see a time-depth recorder tag on her back and a unique hair dye marking on her left side (if you want to know how we mark our seals, check out the video in one of the previous post below!). Where do you think she is right now? Do you think she’s near Oregon or Washington or maybe even Alaska?! We hope to find out soon!
Photo credit: Patrick Robinson
Meet the team!
Dr. Patrick Robinson (top left) is leading the field efforts on this project. He is the Director of the University of California Reserve System’s Año Nuevo Natural Reserve and teaches an undergraduate course called Field Methods in Large Marine Vertebrates. Patrick is an avid photographer and also likes to find other neat critters, like the western fence lizard in the photo below!
Dr. Dan Costa (top right) is a co-investigator on this project and leads the elephant seal program at Año Nuevo. He is a Distinguished Professor at the University of California Santa Cruz and has studied seals and sea lions around the world – from Antarctica to the Galapagos to the Falkland Islands to the Bering Sea – for the past few decades.
Dr. Roxanne Beltran is a co-investigator on this project and will lead the data analysis component of this project. She is a National Science Foundation Postdoctoral Research Fellow and also enjoys mentoring students, teaching classes, and sharing her work with other scientists.
Diana Alvarado is a STEM Diversity program Packard Fellow working on the elephant seal tracking data for her summer internship project. She is interested in comparing the accuracy of different tagging technologies.
How do we decide which seals we want to study? Luckily for us, the seals at Año Nuevo have been studied for the last 50 years. Año Nuevo is both a University of California natural reserve and a California State Park, so the beach is protected from the public and the seals are relatively undisturbed. Each year, about 300 of the newborn pups are given flipper tags that have a unique number, so we have a record of who their mom was, when and where they were born, and each time we see them on the beach. Because the tags are small and hard to see in a big group of seals, we use hair dye to mark each individual seal with a large number. See the video below for some information about marking seals! We have a database with ~40,000 of these tagged seals, each seal’s history at Año Nuevo can help us identify good seals to target for this study. In addition to simply figuring out where these seal pups go and how deep they can dive on their first ocean migration, we also want to know whether their abilities are innate (passed on genetically from mom) or learned (through trial and error). To do this, we can deploy trackers on seal pups that were born to previously-tracked mothers. Comparing the pup’s diving and navigation abilities to the mom’s will allow us to ask some really exciting research questions! We created a list of target seals and we’ll walk across the entire beach next week looking for those flipper tags or marks. Wish us luck!
Our 24 tags have arrived! They are Wildlife Computers MK9 tags and we have programmed them to record diving depth, ocean temperature, and ambient light every 4 seconds. The diving capabilities of these elephant seal pups are a mystery, but we hope they don't dive deeper than the tag limitation of 1,000 meters!
Many species undertake long ocean migrations, but it remains a mystery how young individuals learn to navigate without parental instruction on their first journey. Elephant seals can travel 7,000 miles in the open ocean, but we don't know where the pups go or how deep they can dive. We are tracking 24 elephant seal pups from their first day in the ocean through their first year of life. Our biggest curiosity is whether the navigation and diving abilities of seal pups is innate; in other words, are a pup’s abilities related to those of her mother? Each of the tracked pups has a mom that has already been tracked, and we will compare the mom’s track to that of her pup. We are excited to learn out how these elephant seal pups explore the ocean during their first migration!
Photo credit: Dan Costa
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