Publication Date

Summer 2023

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


Birgitte I. McDonald; James T. Harvey; Cassondra L. Williams


Marine mammals face an extraordinary challenge as they must actively hunt during breath-hold dives. This challenge is conquered by the dive response (the decreased heart rate and increased peripheral vasoconstriction associated with a breath hold) and is influenced by dive duration, depth, exercise, and cognitive control. I studied the dive response of one of the deepest diving marine mammals, the northern elephant seal, across two years to determine interactions between behavioral and physiological factors on a fine scale. I examined the influence of dive depth, duration, and activity (ODBA) on dive heart rate (fH), pre- and post-dive fH, post-dive surface interval and fH at fine scale (20s). Dive depth and duration influenced dive fH more than activity. When analyzed on a fine scale, however, northern elephant seals did adjust their fH in response to activity, primarily in the bottom and ascent phases of their dive. These results suggest that these seals actively regulate their oxygen stores during dives. Overall, these seals are prioritizing oxygen conservation to replenishing oxygen-depleted muscle tissue, as the relationship between dive depth and duration to dive fH was stronger than dive activity to dive fH. They do provide relief to muscle tissue in small increments at fine scale, however, by briefly increasing fH. Their incredibly adapted dive response, exercise modulation, and dive behavior allows northern elephant seals to regularly dive within their aerobic dive limit (ADL) and minimize their recovery time at the surface.