Assessing the Potential for Nitrogen Bubble Formation in Diving Odontocetes

Abstract

Abstract : The goal of assessing whether nitrogen (N2) bubble formation occurs in repetitively diving odontocetes is to address hypotheses related to the stranding of beaked whale species coincident with naval sonar activities. Specifically, data will be acquired that will either support or refute the conjecture that the accumulation of N2 and subsequent formation of N2bubbles is a causative mechanism of beaked whale strandings. The objective of this study are to: 1) train a dolphin to repetitively dive a depth profile specifically created to maximize nitrogen absorption from the lung; 2) following a dive series, ultrasonically inspect the blood vessels of the dolphin for the presence of nitrogen bubbles; 3) determine the partial pressure of N2, or PN2, in arterialized venous blood following a diver series; and 4) relate the partial pressure of N2 to the presence or absence of vascular bubbles. A trained dolphin from the Navy Marine Mammal Program (MMP) was used for the study. Some differences between beaked whales and delphinoids in their respective physiology and anatomy are acknowledged; however, no other surrogate species were readily available or amenable for the proposed testing. The subject was transported via a modified Boston whaler to a deep-water site where it was trained to perform a series of dives to depths between 10 and 100m.