SELECT ANTARCTICA FIELD BLOG POSTS AND ARTICLES
WITH RELATED IMAGES AND SHORT VIDEOS
WHAT WE HAVE LEARNED
In this section we’re highlighting just a few of our findings over the years. Those interested in a more complete list of the project's scientific findings may view the project's Publications page.
Weddell Seals and a Massive Iceberg Event
One of the benefits of such a long-running study is the extensive database built up over the decades on this population of Weddell seals in the Erebus Bay area of Antarctica's Ross Sea.
Because of this unique data set, Montana State University Weddell seal project scientists were well positioned to study the effects of a massive iceberg event in the past decade that blocked the seals' access to many of their usual pupping colony locations in the Erebus Bay study area.
Findings of project scientists were published Sept. 26, 2012 in the international journal, Proceedings of the Royal Society B: Biological Sciences. Lead author of the paper is Thierry Chambert, then a doctoral student supervised by Jay Rotella in the MSU ecology department. Jay Rotella and Bob Garrott are co-authors on the paper, and are Co-Principal Investigators on the Weddell seal population project with Don Siniff.
An abstract of the paper "Environmental extremes versus ecological extremes: impact of a massive iceberg on the population dynamics of a high-level Antarctic marine predator" is now available online at the Proceedings of the Royal Society B: Biological Sciences website.
A project feature short film (please see below) was produced on the subject, entitled "Weddell Seals and a Massive Iceberg Event" that premiered at a Special Cultural Event associated with the 2012 Annual Scientific Committee on Antarctic Research (SCAR) held in Portland, Oregon.
- Mary Lynn Price Adapted Field Blog Article, 20 October 2012 How Do Weddell Moms Matter?
Cohort Effects and Conditions Before Birth
To me, one of the most fascinating studies undertaken by the Weddell seal project is that which uncovered cohort effects in the Weddell seals of Erebus Bay in Antarctica's Ross Sea. The published scientific paper on this topic is “Environmental variation and cohort effects in an Antarctic predator” (Garrott et al. 2012).
A very young Weddell seal pup and her mom.
Cohort, here, refers to all of the Weddell pups born in the Erebus Bay study area in one pupping season, which occurs starting in mid-October and continues until late November each year. What makes this discovery especially interesting is that the scientists were able to take 30 year’s worth of data from 4178 tagged female Weddell pups born into 20 different annual cohorts, and 30 years of mark-resight observation data to discover that there are large differences in the proportion of each annual cohort that survives to return to the pupping colonies and produce a pup within 10 years of their birth. Because Weddell seal females have strong birth area fidelity (natal philopatry) and return to the area of their birth to give birth to their own pups, and it has been found that 93% of breeding females produce their first offspring by age 10 (Hadley et al. 2006), it is likely that Weddell females that have not recruited into the Erebus Bay breeding population within 10 years have died.
Two Weddell seals encounter each other under the sea ice in this video clip by Henry Kaiser, 2009.
The study data strongly supports an association between “cohort recruitment probability” and the regional extent of sea ice experienced by the mother during the winter the pup was in utero (Garrott et al. 2012). Cohort recruitment probability refers to the likelihood of female Weddell seal pups surviving to adulthood and returning to the pupping colonies as adults to give birth to pups of their own.
Weddell seal moms and pups on the sea ice at Big Razorback Island colony.
There are probably many reasons why there are differences in the proportion of females of a cohort that return to reproduce, but project scientists suspect it all starts with whether the fertilized egg of a Weddell seal female implants in her uterus, which may be influenced by the level of nutrition the mom experiences during the austral summer. Another reason would be the level of nutrition the mom experiences in the austral winter as the pup is developing in utero, and the mom is continuing to gain mass.
Two Weddell seals share a breathing crack in the sea ice.
Weddell seal females are “delayed implanters”. They usually mate underwater in early December at the end of the 30 to 45 day nursing period in the late austral spring or early summer. However, the fertilized egg does not implant in the mother’s uterus for a month or two after mating. Although we do not have physiological data, project scientists think that the more food resources available to the Weddell females in a particular austral summer season, the more likely the fertilized egg, or blastocyst, will implant in the mom’s uterus and the embryo will begin to develop and grow.
Project scientists suspect (but don’t really know for certain) that a female starts to regain body mass as soon as she weans her pup. But there is a lot of uncertainty about the dynamics of Weddell mom mass gain—whether it occurs quickly over a month or two, or gradually over many months, and whether the summer is when most mass is gained, or the winter. Or perhaps both summer and winter seasons contribute equally.
Playful pup with sleeping mom, Big Razorback Island and Mt. Erebus volcano in the background.
Delayed implantation of the fertilized egg in the mother's womb is exclusively a summer phenomenon, while overall body mass gain by Weddell moms could be a result of summer or winter conditions, or a combination of conditions spanning both seasons. (Please see the previous post of the 1st section of this writing for more information on Weddell seal females being "delayed implanters.")
Weddell pup nursing on the sea ice with a nearby Weddell colony in the background.
One of the main environmental factors affecting the amount of food available for the Weddell females during winter is the amount of sea ice extent. Scientists have hypothesized that the Ross Sea marine ecosystem is strongly structured from the top down, indicating that high level predators such as Weddell seals have a strong influence on the overall ecosystem. There is thought to be substantial predator competition by minke whales, emperor and Adélie penguins, killer whales (orca), snow petrels, and Antarctic toothfish for food resources such as Antarctic silverfish, a major prey of Weddell seals.
Increased sea ice extent limits access to food resources by competing predators such as whales and birds; and the amount of food Weddell moms can obtain during the winter when their unborn pups are developing in utero may be greater. The more mass the moms can put on, the bigger the pups are likely to be when they’re born the following spring, and the bigger the moms. Bigger moms can transfer more energy and mass to their nursing pups after birth. Bigger pups have a greater likelihood of surviving to reproductive age and recruiting—returning to a pupping colony and giving birth to pups, themselves. Project scientists have concluded that annual variation in food resources available to pregnant Weddell females was likely the driver of variation in recruitment probability among cohorts (Garrott et al. 2012).
One of the most significant findings described in Garrott et al. 2012 is that bigger cohorts do better. So when conditions are such that more females do produce pups, those bigger cohorts have a greater proportion of female pups that go on to become mothers, themselves. It will be particularly interesting to see how the most recent record-breaking or near-record pupping seasons—cohorts—fare in the next several years.
Photo by Bill Link of a mom and pup at Turks Head Weddell seal colony, NMFS Permit 17236.
So from the beginning, Weddell moms and the varying environmental conditions they encounter make a difference in whether the fertilized eggs implant, how much nutrition the unborn pups gets while in utero, how much energy and mass is available to transfer to the pups after birth while nursing and, thus, the likelihood of whether the pups in the particular annual pup cohort recruit—survive to return to the pupping colonies and give birth to pups of their own.
- Mary Lynn Price
Adapted Field Blog Article 24 October 2014
Thank you to Weddell project scientists and cohort effects paper authors Drs. Bob Garrott, Jay Rotella, and Don Siniff for their patient assistance reviewing and ensuring accuracy of this post.
Garrott, R. A. et al. 2012. Environmental variation and cohort effects in an Antarctic predator. – Oikos 121: 1027-1040.
Hadley, G. L. et al. 2006. Variation in probability of first reproduction of Weddell seals. – J. Anim. Ecol. 75: 1058-1070.
Being Different If You're A Weddell Seal in Antarctica
What does it mean to be different if you're a Weddell seal in Antarctica? Our new project video explores individual variation in Weddell seals studied by the Weddell population project research team, and what such individual variation might mean for the future of this southernmost mammal living in the most pristine marine environment on Earth.
Featured in this video are interviews on location in Erebus Bay, Antarctica with ecologists Jay Rotella, Bob Garrott, Thierry Chambert, and Jesse DeVoe on the Weddell population project. The video also showcases some truly spectacular underwater footage by Henry Kaiser, courtesy of the Project B-470 Weddell research team, and lots of Weddell puppies and moms filmed by myself and other members of the Project B-009 Weddell population study research team.
This new project video is made possible with funding and support from the National Science Foundation, and the assistance of the United States Antarctic Program. Produced in association with Montana State University. More information on the project, the seals, and the researchers at WeddellSealScience.com.
Over the years the Weddell project has published a number of scientific papers on various aspects of individual variation in Weddell seals. Among the most recent project publications is a fascinating paper on whether frequency of pupping--how many pups a Weddell seal mom has over her lifetime--is a fixed or real characteristic of these seals, as opposed to a chance, or random, occurance. Researchers found that this life history characteristic involves a fixed trait and, interestingly, one that continues to be expressed in harsh environmental conditions.
- Mary Lynn Price
Adapted Field Blog Article 20 November 2013
A Rare Old Weddell Mom with Her 22nd Pup!
One of the big questions I had for the Weddell Project 2014 Antarctic field team was whether the very old Weddell mom with the study record number of pups had lived to return again to the Erebus Bay Study area, and whether she had a new pup this year. Per Weddell population study lead scientist Jay Rotella, the great news is that she has lived through another winter and returned--and she has given birth to her 22nd pup! This is a new Weddell population study record.
Photo by Jay Rotella of the very rare 31 year old huge mom with her very recently born tiny pup.
This is a very rare old Weddell mom. According to lead project scientist Jay Rotella, who is currently working in the field as part of the 2014 Antarctica field team, what is so remarkable about this Weddell mom is that she has had 22 total pups so far. She produced pups at ages 8, 9, 10, (3 in a row then 1 year off), 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, (16 in a row then 2 years off) 30, and then 31, (3 in a row for the 3 most recent years). Weddell seal moms live an average of 15 years, and usually have around 2 pups every 3 years, so this long life and frequency of pupping is very unusual.
Photo by Jay Rotella of this year's view of part of the Hutton Cliffs Weddell seal colony on smooth 1st year ice.
All of the pups of SPENO 5970, as she's known in the database, were born at Hutton Cliffs. For the past several years Hutton Cliffs has been a rugged area with jumbled multi-year ice, hummocks, and rough sastrugi. This year the ice is smooth 1st year ice; and much of the seal colony can be seen for some distance on the flat terrain.
This rare old mom was born in 1983 at an area called the North Base of the Erebus Glacier Tongue. This area is relatively close to the Hutton Cliffs pupping colony, where all of this Weddell mom's 22 pups have been born over her reproductive life to date.
Close-up of the old mom and her 22nd pup this 2014 season, photo by Bill Link, NMFS Permit 17236.
Because of the longterm dataset of the Weddell seal population project, the researchers are able to keep track of the Weddells in the study area and access data on over four decades of seals and several generations. Working with the extensive database, lead population study scientist Jay Rotella was able to determine that of SPENO 5970's first 21 pups, 11 were females and 10 were males. "Of those offspring, 2 sons and 2 daughters have been seen again, which is right in line with what we'd expect based on other analyses indicating that roughly 20% of the seals make it to adulthood." Her new pup is a female.
Another portrait shot of the old mom and her 22nd pup this 2014 season, photo by Bill Link, NMFS Permit 17236.
Of SPENO 5970's surviving offspring, two daughters have returned to the pupping colonies to give birth themselves. One of those daughters is 23 years old and has produced 13 pups so far. One of that daughter's pups--a granddaughter of SPENO 5970--has gone on to have 5 pups herself.
Photo by lead scientist Bob Garrott of old mom in 2013 with her 21st pup showing the rugged terrain of Hutton Cliffs last year.
According to the database, Rotella notes that the old Weddell mom has at least 14 grandpups and 5 great grand-pups. We look forward to more photos of SPENO 5970 from the team this year as her 22nd pup gets bigger and bigger!
Photo by 2014 field team leader Terrill Paterson taken last year of old mom's 21st pup growing larger.
- Mary Lynn Price
Adapted from a Field Blog Article 28 October 2014
These Articles Have Been Adapted From Select Antarctica Field Blog Posts
Created Over the Years During the Weddell Seal Pupping Season. The Entire Weddell Seal Science Field Blog Can Be Found Here. Return to Main Select Articles Page