Sperm Whales in the Gulf of Mexico

New research about sperm whales in the Gulf of Mexico continues to suggest they are a distinct population.

Until a few years ago, scientific research on the whales was limited to basic knowledge of their range, an area just south of Western Florida Panhandle to the South Coast of Texas, and a rough estimate of their population, approximately 1,100.

A June 2006 report done for the Minerals Management Service by the Department of Oceanography at Texas A & M University provides an initial set of data that more clearly defines stock characteristics. Because oil and gas interests plan to construct deep water operations in the sperm whale habitat, one part of the study examined the relationship between anthropogenic noise and whale behavior.

The report runs over three hundred pages, reviewing and offering tentative conclusions about the range of experiments and observations undertaken by a team of scientists. Sample populations were observed, photographed, and/or tagged with tracking devices to determine basic characteristics such as gender, age, size, communication and feeding behaviors. Biopsies were taken to begin building a genetic data base. One common theme underlying the research, with the exception of the sound experiments, focused on testing the hypothesis that the whales were a distinct population.

The following brief summary of results provide some of the more interesting tentative conclusions.

Satellite tracking done on 39 whales between 2001-2004 shows them to be a stay at home group of whales inhabiting an area just south of Western Florida Panhandle to the South Coast of Texas. Gender and age differences explained some basic range and movement activities within the sample group. For example, a group of females and juveniles appear to favor living and feeding in an area around Mississippi River Delta and Mississippi Canyon. Mature and maturing males displayed a tendency to extend both their horizontal and vertical ranges.

A sample of 52 sperm whales measured smaller on average than sperm whales found in the Gulf of California. Scientists hypothesize size as a function of environment and food sources. The smaller size of sperm whales in the Gulf of Mexico may be related to the relatively smaller size of the Gulf (compared to other sperm whale habitats) and the smaller food sources available.

Sperm whales are considered a social and chatty species of whales. When gathered as a group, they exhibit a specific type of vocalizing called a coda. The coda of a sample population of whales was taken, and initial results from a dendrogram (mathematical way to chart sounds) shows they use a distinct dialect compared to codas of sperm whales in the Azores, Caribbean and Mediterranean Seas.

Sperm whales use echolation, (their built in sonar) as a navigation and feeding tool. There is a growing body of evidence suggesting that anthropogenic noises harm whales, perhaps by knocking out their sonar. Since oil and gas drilling operations use sonar for generating seismic survey arrays of potential development areas, one series of studies sought to understand how noise from ongoing or potentially new oil and gas operations in the Gulf of Mexico might effect the sperm whale population.

The only solid conclusions they reached were that whale feeding habits were altered by initial sound experiments, and more research was needed (p 254(272).

"While these results should not be considered conclusive, this study does provide some evidence that air guns affect the foraging behavior of sperm whales, and should help define hypotheses about effect size and describe natural variability in these important behaviors...

Our study also had lower statistical power than originally planned because of decisions made by governmental funders and industry partners to reduce the field effort, which reduced the power of the study. In fact, additional trials were planned for 2004, but governmental funders and industry partners cancelled the scheduled research and redirected research funds to other activities."

© 2007 Patricia A. Michaels