What can live upwards of 200 years, dive to depths of 500 feet, break through sea ice with its head to take a breath of air, weigh more than 75 tons yet sustain itself on tiny zooplankton such as copepods and euphasiids (krill)?
If you guessed the bowhead whale you are correct! Bowhead whales appear to be the longest-lived mammals on our planet. Pretty amazing.
Here in Barrow it's still a little stormy out on the Arctic Ocean so I’m learning more about whales this morning! Sitting in the hall in front of a Bowhead Whale Aging Study poster I can see that as part of this study the whales sampled were found to be between 1 and 135 years old! Listening to local wildlife biologists it appears that more recent data supports the whales living more than 200 years. Wow! During our PolarTREC Polar Connect webinar yesterday there were many really terrific questions asked by those who joined us about the bowhead whales. So many questions and topics that I think it's best to point you to the experts here at the North Slope Borough Department of Wildlife Management. Their offices are right up the hall from our lab room here on the UIC-NARL facility. I'll address the age issue here and at the end of the journal you'll find a link to the North Slope Borough Department of Wildlife Management website that has the most current information and research studies conducted on the bowhead whales! Under Documents you'll also find some great information on the 2013 Calender:The Life of a Bowhead Whale. Please note that the first page of the pdf document lists all those involved in the creation and publication of this calender.
There are several methods that scientist use to age the whales.
Baleen carbon aging
Baleen aging is based on the whale’s consumption of an invertebrate diet that contains varying amounts of carbon. The invertebrates the whale eats in the Bering/Chukchi Sea have higher levels of carbon than the population it feeds on while in the Beaufort Sea. The bowhead whales migrate between the Bering/Chukchi Seas in the spring and the Beaufort Sea in the summer. Every year a sea carbon cyclic pattern develops within the whales baleen plate. By analyzing a small section of the baleen and counting the number of carbon peaks, scientists can roughly determine the age of the whale. A downside to this method is that as the whale ages this method becomes less useful because as the whale grows its baleen wears off at the tip.
Ovaries aging
A second way to age a bowhead is to analyze a female’s ovaries. Each time a female bowhead whale becomes pregnant, a small area of scar tissue called copus albicans appears in the ovary. Scientists believe that these scars are retained for life. Count the ovary scars and you can get a good idea of the age of the female bowhead whale.
Stone weapons
A third way to age the whales is by examining old stone weapon fragments found imbedded in recently deceased whales. These weapons have not been used locally since the late 1800s and researchers at the Smithsonian Institute believe the harpoon tips found are from the 1700's. Finding these weapons can give scientists and Inupiat indirect evidence that some whales are easily more than 100 years old.
Poster of stone weapons found recently in bowhead whales. Poster location: Hallway wall outside of North Slope Borough Department of Wildlife. September 8, 2012. Photo by Lisa Seff.
Aspartic acid racemization and whale eye lenses
Finally, the method to determine the age of the whales that caught my attention the most was the aspartic acid racemization. Deceased whale’s eye lenses are examined to determine levels of two different forms of aspartic acid. When a whale is born its eye lenses contain one hundred percent aspartic acids in Form “A”. As the whale ages that acid changes into Form “B”. The amount changed acts like a natural clock and allows researchers to have a good understanding of the whale’s age. If you understand the process of radiometric dating, the idea is similar. When something changes from one thing to another at a known rate, the amount that remains can tell you how long a process has been occurring. If you'd like more information on amino acid racemization please see the attached document from Today's Chemist At Work!
Pretty amazing isn’t it. In the end scientist like to utilize several methods to determine the age of the whales. If the results from different methods are similar they have a much higher confidence in their estimates of the actual age of the whale.
Well, it looks like the wind has dropped and we're heading out for another Sea Cruise, which means it's time to put on my layers, boots and rain gear! Check back later to see which transect we sampled from and what we found!