Cold Water Contributed to Recent Surge in Dolphin Deaths
Unusually cold water in 2009-10 and 2010-11 contributed to the death of dozens of young dolphins in the Gulf of Mexico, researchers report.
Snowmelt Chilled Gulf
Researchers attribute the deaths of 86 dolphins that were either aborted or died shortly after birth in 2011 to cold water in the Gulf. The culprit may well be fresh water from snowmelt far to the north that was carried to the Gulf by the Mississippi River. Researchers note that water temperatures fell in Mobile Bay and the Mississippi Sound three weeks before each peak in infant dolphin deaths.
“There appear to be several factors contributing to the excess deaths of infant dolphins in the Gulf coast waters in 2010 and 2011,” said William Balgord, Ph.D., a geochemist and president of Middleton, Wisconsin-based Environment and Resources Technology, Inc. “But the close correlation between multiple instances of aborted and deceased neonatal offspring of the marine mammals observed to follow successive dips in inshore Gulf water temperatures is noteworthy in itself.
“Repeated surges of chilled Mississippi River water, contributed from the Rocky Mountains, Plains, and Midwestern states during the normal progression of spring thaws after winters of unusually heavy snow accumulations, augmented by heavy April 2011 rains in the Missouri River basin, lends credence to the theory that hypothermia played a part in the mortality,” Balgord explained. “Heavy flooding in April spilled into the Gulf of Mexico from the main channel and other distributaries. Chilled water repeatedly spread out along the inshore eastward into Alabama and to the western edge of the Louisiana coastline.”
Ruth H. Carmichael, senior marine scientist at Alabama's Dauphin Island Sea Lab, agreed with Balgord’s analysis.
"These freight trains of cold fresh water may have assaulted them, essentially kicking them when they were already down," Carmichael told the Associated Press.
Stillbirth Protects Mothers
“Similar phenomena, but not directly connected to acute hypothermia, affect the fertility of deer herds during winters when deep snow covers the woods and fields of the Midwest and New England,” said Balgord. “After snowy winters a gestating doe may deliver a single fawn or none at all. Typically, white-tailed doe give birth to twins or even triplets, when food is abundant. But if scarce or difficult to reach because of deep snow, her fetal tissue may be resorbed during the lean months to preserve the life of the mother, as a survival mechanism of the species.”
Balgord suggests “a stressed late-term dolphin may react with a similar response and deliver a premature or stillborn calf when challenged by atypical cold and/or a combination of other adverse environmental conditions.”
Bonner R. Cohen, Ph. D., (firstname.lastname@example.org) is a senior fellow at the National Center for Public Policy Research.