ARGOS USER STORIES
Written by: Josh London, Michael Cameron, and Dave Withrow
Edited by: Thomas Gray (CLS America)
Alaska Fisheries Science Center's Marine Mammal Laboratory
Polar Ecosystems Program
Note: All research conducted and photos collected under the authority of MMPA Permit No. 19309. Full story and blogs located here.
The Alaska Fisheries Science Center's Marine Mammal Laboratory conducted an ice-associated seal research survey in the central Bering Sea from April 2-29, 2016 aboard the NOAA Ship Oscar Dyson. The species being studied are ribbon, spotted, bearded and ringed seals.
The key objective of the project is to attach Argos satellite-linked tags on ribbon and spotted seals, which spend time either on or in the proximity of sea-ice during this time of year. Scientists plan to use data collected from the satellite-linked tags, together with information collected during similar surveys since 2005, to learn more about the timing of when these seals "haul out," that is come out of the water onto the ice. This information is critical for calculating abundance estimates from aerial surveys. Scientists also hope to learn more about dive behavior and seasonal movements (useful in identifying important habitat).
Eight biologists are on our field team: Gavin Brady, Michael Cameron, Shawn Dahle, Josh London, Dave Withrow and Heather Ziel from the Center, Charles Littnan from NOAA's Hawaiian Monk Seal Research Center and Markus Horning from the Alaska SeaLife Center. Our veterinarian is Deborah Fauquier from NOAA Fisheries' Office of Protected Resources. A typical day begins with transiting along the edge of, and within the, marginal pack ice looking for seals to tag.
We timed the survey to coincide with the whelping, nursing, and pup maturation season. Ribbon and spotted seals give birth to pups on the ice. Pups are nursed for 25-35 days before being weaned.
Seals prefer thicker, stronger ice floes that remain stable for this activity. However, at this time of the year, much of the marginal ice zone consists of young, thin ice formed late in the winter that is easily broken up and dissipated by ocean swells. This makes it difficult for seals to find stable places to haul out and challenging for our research team to capture them for tagging.
One way we find spotted seals is to look for a "triad." Adult male spotted seals will often find a mother and her pup on the ice and remain with them until the female is ready to breed. Collectively they are called a "triad."
To tag seals we attach satellite transmitters to their hind-flippers (SPOT tags, Wildlife Computers, Redmond, WA). These tags provide long-term movement data and haul-out timelines. However, the tags only transmit data when the seal is hauled-out and their flippers are exposed.
We will also try to attach head or back-mounted tags (SPLASH, Wildlife Computers, Redmond, WA) to most of the seals. This will provide more detailed information about locations at sea and seal diving behavior. These tags are adhered to the hair with super glue. Adult spotted and ribbon seals undergo an annual molt in May and June and so the SPLASH tags are expected to provide data for only a few weeks or months before being shed. In addition to location estimates, the SPLASH tags provide important behavioral data. Diving is an indicator of foraging activity and long periods at the surface indicate haul-out and resting behaviors.
The sampling for each seal typically includes morphometrics (i.e., length, girth and mass measurements) and the collection of numerous tissue and fecal samples for studies of pathology, genetic population structure, blood chemistry, diet, contaminants, health and condition. These samples will begin to form a reference against which future impacts of climate disruption and loss of sea ice can be assessed. -Michael Cameron
You can read more about the research conducted by the team along with all of the blog entries and images here (http://www.afsc.noaa.gov/Science_blog/IceSealEcology_main.htm).
We wanted to share the intoduction, above, and a snapshot of the data gleamed from the tags, below, to give you a general idea of the processes these teams go through in order to research these polar-based seals. The text, graph, and images below are all courtesy of NOAA Fisheries and written by Josh London.
Working up a seal with a portable ultrasound. Image: Dave Withrow
A spotted seal with an Argos transmitter atop its head. Image: Dave Withrow
The team is gluing the tag to the seal's head. Image: Josh London
A young ribbon seal. Image: Dave Withrow
The dive plotted grap, above, belongs to a sub-adult ribbon seal captured early in the cruise. For the first few days, the seal was diving to about 140 meters. This is the approximate depth of the Bering Sea shelf and we can presume the seal was diving to the bottom in search of fish to eat. Later in the record, the seal made several dives to 400 meters, exceeding 500 meters a few times—that's almost 3x the height of the Space Needle (in Seattle, WA)!
The map of locations shows the movement of this seal, and you can see that those deeper dives coincide with movement off the Bering Sea shelf into much deeper water. In later days, the seal turned around, making its way back to the ice. Many sub-adult seals are molting at this time of year. Growing a new coat of hair requires quite a bit of energy, thus it makes sense that this seal would spend some time in productive waters, bulking up on fish, before returning to the ice to molt.
After release, the adult female ribbon seal spent most of her time at the surface—likely on an ice floe to nurse her pup—but also included several foraging periods with some dives 150-200 meters in depth. Over the next few days, and as the pup gets older, the time she spends foraging increases.
For comparison to the ribbon seal (mentioned in the above paragraph), the dive plot directly above this paragraph shows the diving behavior of an adult female spotted seal. Note there is some foraging, but not as much as we see in the ribbon seal example. With only a few animals tagged, it isn't possible for us to know if these differences are true differences between species or just a representation of the various behavior strategies of mother seals.
Disclaimer: This an example of how these tags can be used. It is not meant as a product endorsement by NOAA's National Marine Fisheries Service.