Special Field Report By Dr. Elizabeth Flesch:
Where do the mystery seals come from??
Granite Harbor, perhaps?
One of the reasons we can gain so much information from studying the Weddell seal population in Erebus Bay is because the seals who are born there typically return as adults to have their own pups in the same location. Because we tag every seal who is born in the study area each year, we can identify seal moms who originated in a different area due to a lack of tags. Every year our team observes moms lacking numbered tags who come in from other areas to have their pups. We are interested in learning from where these moms are coming and what might affect their decision to give birth in Erebus Bay, instead of their natal colony. It is quite a mystery!
We are genetically sampling other Weddell seal colonies at a variety of distances from the Erebus Bay study area to find an answer to these questions. The project has now sampled inside the study area and at four Weddell seal colony sites along the Victoria Land Coast: (1) Marble Point (~87 km away from McMurdo Station), (2) Granite Harbor (~137 km from McMurdo Station), (3) just south of the Drygalski Ice Tongue (~262 km from McMurdo Station), and (4) in Terra Nova Bay (~364 km from McMurdo Station).
Cursor over the dots in the map above to identify the Weddell seal pupping colonies
visited outside the Erebus Bay study area to obtain Weddell seal genetic samples.
This interactive map was prepared by Dr. Jay Rotella.
To obtain a genetic sample, we take a small piece of tissue from a seal’s hind flipper. Don’t worry about our impact on the seals; in the wild Weddell seals bite each other on the hind flippers, and our efforts have comparatively less of an effect. Some of them snooze right through it, and all of them go back to sleeping within minutes of being sampled.
Preparing Weddell seal genetic sample vials for use in the field.
Today we visited Granite Harbor to collect genetic samples from 33 moms there! We flew by helicopter to Granite Harbor, which is about 80 miles from Erebus Bay. Once there, we split into multiple groups to collect the samples. We also checked for tagged animals while we were at Granite Harbor, and we found one female who was actually born in Erebus Bay, which suggests that there might be a very minimal amount of animals exchanging between the two populations. Hopefully these genetic samples will help answer how much exchange is going on. Once the tissue samples are collected, we split them in half and store them in ethanol in a -80C freezer. Splitting them in half creates redundancy so in case something happens to one batch, we still have the other batch.
The 2023 field team as they head out to visit the Weddell seal colony at Granite Harbor, Antarctica.
Photo by Brian Minnear.
We have also sampled three other seal colonies to compare with Erebus Bay. Using modern sequencing technology to analyze the seal DNA, we can evaluate how related the seals found in different locations are. Based on that information, we can determine the most likely birthplace of the mystery moms found in Erebus Bay. We look forward to sharing those results in the future!
- Elizabeth Flesch (she/her)
Montana State University PostDoctoral Researcher working with Weddell seal population genomics collaborative project Principal Investigator, Dr. Nancy Chen of the University of Rochester, and co-advised by Dr. Jay Rotella of Montana State University.
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