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Science
Volume 40 Issue 1 • April 22 - May 5, 2010
now in our 40th season

Mythbusters!

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

For the past seven years, the Discovery Channel has featured a show called Mythbusters which is hosted by Jamie Hyneman and Adam Savage and co-hosted by Tory Belleci, Kari Byron and Grant Imahara (http://dsc.discovery.com/tv/mythbusters). Each episode tackles one or more myths and investigates their validity from a scientific viewpoint. The hosts have a ton of fun building outlandish contraptions and blowing things up. Nantucket’s isolation and atmosphere lends itself to a wide variety of myths, so I thought it would be fun to talk about a couple of them in today’s column.

You may have seen some letters in the paper about our burgeoning seal population and wondered, how many seals are we supposed to have or what is the natural gray seal population? 

Many people mistakenly believe (Myth #1) that our seal population is higher now than it has ever been before.

From a column I wrote earlier this season (http://www.yesterdaysisland.com/2010/science/16.php ): “Gray seal populations plummeted from the colonial era to the 1950s due to hunting and extermination programs by people who believed that the seals were out-competing them for cod.  By 1950, the numbers of gray seals south of the Canadian Maritimes were less than 50 individuals and they were effectively considered extirpated (see note below).  A bounty on seals of five dollars per nose caused a decline of all seals in Massachusetts waters.  By the beginning of the 1960s, this had reduced the number of gray seals to about fifteen.  Then, in 1962, the state outlawed the killing of seals, and since 1972 they have been under federal protection under the Marine Mammal Protection Act, which makes it a federal crime to kill, harass, or disturb a marine mammal by approaching within 150 feet or doing any action that changes its behavior (which would include cutting off its nose).  Due to this protection, approximately 4000-6000 seals have been recorded around Nantucket in the past five years with 1892 pups born in 2005 on Muskeget.  The entire Western Atlantic population is estimated to be around 250,000 individuals and the Eastern Atlantic population is thought to be around 150,000-200,000 individuals.” It is important to note that although extirpate means “to destroy or eliminate completely” it is not necessarily synonymous with extinction, since extirpate may be applied to circumscribed populations within the range of a given species, so it might be said that such-and-such a population has been extirpated, even though the species as a whole is still extant. And we are seeing that in action now as a few individuals left behind repopulated the area in addition to some recent northern migrants that are moving down to haul out sites nearby as Cape and Island shoals become desirable locations.

The population of gray seals is still growing locally at around 12% (Sable Island peaked at 12-13% for 40 years and the population growth there has declined to 7%) and has not reached the number of individuals that could be supported by the available food and territory in the past. I know that is no consolation to fishermen who don’t enjoy having their catch removed from their line before they can reel it in, but in a nutshell, they were here first and their populations have not reached a level in which any culling tactics should be employed or would be allowed under the current Marine Mammal Protection Act.

Dietary studies show larger fish like bass and bluefish make up a very small part of gray seals’ diets. Dr. Kristin Ampela has spent the past several years studying the poop (scat) of our local gray seals and finds most of their diet consists of windowpane flounder, silver hake, sand lance, squid, skates, and gadid species such as cod, haddock, and pollock. According to area gray seal experts, our gray seal population will keep on expanding at the same approximate rate that is occurring now until they run out of room to breed and haul out and reduced access to mates and disease and predation start to reduce the population (more info accessed November 14th, 2010 at
www.nefsc.noaa.gov/press_release/2009/SciSpot/SS0901/Seal%20spotlight%20final.pdf

Recently, an archeologist with many years of experience doing research on Nantucket by the name of Mary Lynne Rainey visited the island to give presentations on Wampanoag architecture and related artifacts at both the Nantucket Field Station and the Nantucket Historical Association’s Whaling Museum. Mary was also unveiling a recently released book she co-edited with Elizabeth S. Chilton entitled, Nantucket & other Native Places: The Legacy of Elizabeth Alden Little. The book summarizes noted Massachusetts archeologist Elizabeth Little’s research here on Nantucket and throughout the Commonwealth.  Nantucket long history of professional and amateur “digs” is also chronicled in the book.

What does this have to do with “Mythbusters”?? Well, many questions that pop up here on Nantucket revolve around our existence as an island in relation to the plants and animals found here and several chapters in the book help answer some of the questions historians have had about the Wampanoag’s lifestyle. Today’s subjects involve some components of their diet. When we think about what animals were present it is important to remember that we were connected to Cape Cod prior to the end of the most recent glacial period and any ambulatory creature could have existed here.

Over the years, there has been much speculation regarding our island’s white tail deer population.

Myth #2: “They [deer] are not native to Nantucket, but were introduced in 1922, a time when deer were quite rare in the northeast.”

Contrary to popular belief, there were indeed deer on the island when we first became an island as the Sound filled with water from the melting glaciers several thousand years ago. Records of bones found in archeological digs verify that deer are not just a recent phenomenon, although throughout the last thousand years their population has varied greatly, becoming virtually non-existent on the island in the late 1800s and early 1900s. From records of the Nantucket Historical Association we find this paper regarding the remains of dwelling sites uncovered as a result of island excavations during the building of the Polpis bike path (www.nha.org/history/hn/HNrice-polpis.htm).

“In the study of Native American architecture, the Polpis Road investigations provided evidence that traditional house sites were established on Nantucket during the Late Archaic to Early Woodland Period, about 3,000 to 3,500 years ago, and were used well into the seventeenth and early eighteenth centuries.”

“Based on the wide range of animal species identified from food remains, deer, rabbit, raccoon, and seal were potential sources of food as well as skins for clothing, bedding, or wigwam coverings. Mats made of reeds, sedge, and grasses were certainly used to line floors, based on the thousands of grass seeds recovered from floor deposits. Various species of sedge were collected from coastal wetland margins, providing one of the principal raw materials used in the production of baskets, mats, bags, and in some cases clothing (Wood 1977; Josselyn 1674, 1865; Morion 1838). The importance of these resources to Nantucket's Native population is documented in seventeenth- and eighteenth-century English land transfers and court records (Worth 1992), and is now supported with archaeological data.” I found the reoccupation of some of the homestead sites year after year and decade after decade fascinating. That about 70,000 unique samples (chips, shards, bone and seed fragments, etc.) were collected from 4 sites also sounds to me like not only an impressive amount of material to catalog but also the world’s hardest jigsaw puzzle!

Further evidence is listed in a paper by Elizabeth A. Little and Margaret J. Schoeninger entitled “The Late Woodland Diet on Nantucket Island and the Problem of Maize in Coastal New England”( American Antiquity, Vol. 60, No. 2 (Apr., 1995), pp. 351-368) which was published by the Society for American Archaeology (accessed via http://www.anthro.ucsd.edu/Faculty_Profiles/margaret/Little&Schoeninger1995.pdf on November 14th, 2010).

“Today's list of native mammals includes only deer, mice, voles, and bats, but shell deposits (middens) contain remains of deer, dog, raccoon, fox, muskrat, vole, and mouse. Barbara E. Luedtke (personal communication 1989) analyzed a pit at Quaise, Nantucket, containing bone that was, by weight, 63 percent mammal (76 percent deer), 37 percent fish (24 percent sturgeon), and 1 percent bird - a pattern found also at Nauset on Cape Cod dating between cal A.D. 970 and 1340 (Borstel 1984; Fitzgerald 1984). It is not possible to estimate the actual contribution of each of these categories to prehistoric human diet, since the overwhelming weight contribution by shells and terrestrial mammal bone may reflect preservation and discard patterns rather than actual use.” Other items found on the Nantucket native menu: some maize, lobster, dogs, lots of fish and marine mammals, and eels. Marine mammals and oceanic fish dominated the isotopic signature comprising between 40-65 % of the total remains. Although the deer may have been brought over in trade with mainland tribes, the value of unearthed trade items has been much more significant with items like eagle talons and manmade items discovered. The number of sites and amount of material indicate that these deer (and their seal brethren on the dinner table) were most likely locals. Of course, that doesn’t mean they were immune to overhunting in the ensuing years.

Complicating matters when sifting through the remains of someone’s larder or campfire from hundreds of years ago is where items are cleaned for eating and what bones are used for tools or adornment or discarded. Then, as now, many fish would have been cleaned on the shoreline where scavengers like crabs could dispose of the stinky leftovers. Carbon-13 and nitrogen-15 isotope measurements are indispensable for determine the ratio of plants and animals that have contributed to our diet. These numbers vary based on the trophic level of the associated animal and based on the processes that occur within plants. The tricky part is in determining what those ratios mean. These same techniques are used to look at mummified remains of Archaic and modern homo-sapiens skeletons to find out how we have survived and what we ate over time. A marine plant based creature will have a very different isotopic signature than a land based one; and as you eat higher up the food chain, those numbers also change. Next season we’ll compare those numbers in a variety of fish in a typical pond on the Cape to see how scientists use those to see what’s on the menu. To learn more about mammals on the island and in the Massachusetts, I recommend the Division of Fisheries and Wildlife site which chronicles the current knowledge of mammalian occupants in any specific Massachusetts county: www.mass.gov/dfwele/dfw/wildlife/facts/mammals/mammal_list.htm. I like to check that list frequently. Wildlife biologists are coming to the island to re-evaluate if we still have jackrabbits and if any New England cottontail rabbits can be found.

There are many other “mythbuster” type questions we can explore in next year’s columns so whether you are interested in the prickly pear cactus that can be found on Coatue or in age of our groundwater or amount of salt intrusion, we’ll look at the facts and evidence and use our best powers of observation to determine what is true and what is myth. For now, we won’t be blowing anything up, but you never know. Have a great holiday season and be sure to celebrate everything that makes Nantucket special.

For more seal info: www.nmfs.noaa.gov/pr/pdfs/sars/ao2008segr-wn.pdf

 

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