Journal of Comparative Physiology B

, Volume 174, Issue 2, pp 139–147

The development of diving bradycardia in bottlenose dolphins (Tursiops truncatus)

Original Paper

Abstract

Bradycardia is an important component of the dive response, yet little is known about this response in immature marine mammals. To determine if diving bradycardia improves with age, cardiac patterns from trained immature and mature bottlenose dolphins (Tursiops truncatus) were recorded during three conditions (stationary respiration, voluntary breath-hold, and shallow diving). Maximum (mean: 117±1 beats·min−1) and resting (mean: 101±5 beats·min−1) heart rate (HR) at the water surface were similar regardless of age. All dolphins lowered HR in response to apnea; mean steady state breath-hold HR was not correlated with age. However, the ability to reduce HR while diving improved with age. Minimum and mean steady state HR during diving were highest for calves. For example, 1.5–3.5-year-old calves had significantly higher mean steady state diving HR (51±1 beats·min−1) than 3.5–5.5-year-old juveniles (44±1 beats·min−1). As a result, older dolphins demonstrated greater overall reductions in HR during diving. Longitudinal studies concur; the ability to reduce HR improved as individual calves matured. Thus, although newly weaned calves as young as 1.7 years exhibit elements of cardiac control, the capacity to reduce HR while diving improves with maturation up to 3.5 years postpartum. Limited ability for bradycardia may partially explain the short dive durations observed for immature marine mammals.

Keywords

Heart rate Bradycardia Dive response Development Dolphins 

Abbreviations

ADL

aerobic dive limit

cADL

calculated aerobic dive limit

ECG

electrocardiogram

HR

heart rate

TDR

time–depth recorder

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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  1. 1.Ecology and Evolutionary Biology Department, Center for Ocean HealthUniversity of CaliforniaSanta CruzUSA
  2. 2.The Dolphin ExperienceFreeportBahamas

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