Belly up or belly down: Effect of body position on snout vent length and total length measurements in American crocodiles (Crocodylus acutus)

Abstract

The interpretation of morphometric data is relevant to understanding biological phenomena. Currently, little is known about the effect of body position on morphometric measurements in crocodylians as well as the extent to which these data are interchangeable. We investigated the effect of body position on snout-vent-length (SVL) and total-length (TL) measured ventrally (belly up) and dorsally (belly down) on 725 Crocodylus acutus (mean TL ventral and dorsal 68.49 cm and 69.82 cm, range = 33.1-185.4 cm and 33.8-185.4 cm) across South Florida, United States. We found evidence that body posture significantly influences SVL and TL measurements. However, regardless of body position, the variation found in SVL was less than 1 mm, and for TL was on average only 3 mm. We concluded that even though there is a difference when measuring American crocodiles belly up and belly down, there is a minimal effect on the outcome (less than half centimeter), which falls within the normal measurement instrument error (i.e., measurement tape) even more so under field conditions. If researchers concur that this is an acceptable error, then SVL and TL measurements taken belly up or belly down can be used interchangeably.