Underwatertimes.com News Service - May 26, 2011 10:31 EST

It's an alligator-eat-alligator world out in the waters of Orange Lake in Alachua County, Florida. Cannibalism among American alligators is responsible for a 6–7% reduction in the number of juvenile gators here each year, according to a new study. This number is based on the recovery of marking tags from the stomachs of harvested alligators.

The study, published in the June 2011 issue of the journal Herpetologica, analyzes the probability of recovering tags from alligator stomachs. These are marking tags placed in the webbing of an alligator's right rear foot during previous catch, tag, and release studies. It is also the only thing that remains after an alligator has been cannibalized.

Using marking and recapture records, the researchers were able to collect information on the total number of alligators tagged, year of tagging, the alligator's pod or sibling group, and the alligator's total length—an indication of its maturity. Less than 1% of recaptured alligators showed tag loss, making this a negligible factor.

To test the probability of tag retention in alligators' stomachs, 10 alligators at a commercial alligator farm were each force-fed five tags attached to food. Nine radiographs were taken of the alligators' stomachs up to 588 days after the tags were consumed. After 588 days, the alligators still retained 76% of the tags in their stomachs.

At Orange Lake, 56 tags were found in the stomachs of 33 wild alligators. One stomach contained 14 tags; one contained six tags; two contained three tags each; one contained two tags; and 28 stomachs contained one tag each. From records available for 54 of these tags, researchers determined that 91% of the consumed alligators were no more than 3 years old.

Cannibalism appears to be an appreciable source of mortality for juvenile alligators on Orange Lake and may help regulate the population, the authors conclude. Even the low, 6–7% rate of cannibalism this study found can be an important factor. The impact of cannibalism is a variable that can also affect environmental and population management programs.

Full text of the article "Mortality of American Alligators Attributed to Cannibalism," Herpetologica, Volume 67, Issue 2, June 2011, is available at http://www.hljournals.org.