Native Alaskans who hunt the bowhead whale recognize a less common form of bowhead whale they refer to as the Ingutuk which has short baleen, dense bones, larger girth, and flukes and flippers somewhat differently shaped than other bowhead whales. Various explanations for these whales include that these animals are young bowheads recently separated from their mothers and carrying large stores of energy including a layer of fat beneath the blubber (separated from the blubber by a thin muscle layer), and large stores of calcium in their bones to support rapid growth. It has also been previously postulated that they could represent an inborn genetic error, perhaps of metabolism.

Samples from an 8.4 meter male bowhead whale judged an Ingutuk and an 11.3 meter male bowhead of regular morphology were examined. Blubber lipid composition was determined by thin layer chromatography, high performance liquid chromatography, and gas chromatography of samples of abdominal fat, fat beneath the blubber, and subsamples from three depths from blubber from 5 sites on each whale. Blubber morphometrics were measured on frozen blubber cores from the five sampling sites. The smaller Ingutuk whale had thicker blubber over all, a thicker epidermis and thicker papillary layer as well as a lesser amount of dense white fibrous connective tissue in the reticular dermis than the longer regular bowhead whale. If the smaller whale were a terrestrial animal, these findings could be interpreted as compatible with a manifestation of congenital hypothyroidism, although the marked differences in length between these two specimens makes it impossible to rule out maturational differences as an explanation. The smaller whale also had markedly fewer long chain and polyunsaturated fatty acids in superficial and deep portions of the blubber layer compared to the longer whale. This study was supported by a grant from North Slope Borough, Department of Wildlife Management, Barrow, Alaska.