http://www.digitaljournal.com/tech-and-science/science/scientists-make-first-recordings-of-blue-whale-heartbeats/article/562750

Scientists make first recordings of blue whale heartbeats

Posted Dec 1, 2019 by Tim Sandle
Marine biologists have made the first recordings of a blue whale's heart rate. The activity was slow and tricky. The recordings reveal that blue whale hearts are operating at extremes.
The blue whale (Balaenoptera musculus) is a marine mammal belonging to the baleen whale parvorder  M...
The blue whale (Balaenoptera musculus) is a marine mammal belonging to the baleen whale parvorder, Mysticeti.
"Mike" Michael L. Baird (CC BY 2.0)
To undertake the feat, precise and sensitive monitoring equipment was required. Marine scientists from Stanford University, carefully stored the instrumentation into a neon orange plastic shell and positioned these close to the blue whale (Balaenoptera musculus) target. The device was secured using four suction cups located close to the whale's left flipper.
The heart beat recordings were made using electrodes embedded positioned in the center of two of the suction feet. The data captured the tag's journey and captured the heart rate of a blue whale. The measurement suggests that blue whale hearts are operating at extremes – and may limit the whale’s size. This is based on the analysis of the data which infers that the blue whale's heart is close to working at its limit, and this fact probably explains why blue whales have never evolved to be larger. A typical blue whale is close to 30 meters (98 ft) in length and with a maximum recorded weight of 173 tonnes.
The mission and a snippet of the recording is shown in the following video:
When the whale dives, its heart rate slows to four to eight beats per minute. As it consumes prey, the heart rate rises about 2.5 times the minimum. When the whale surfaces, its heart rate increases to 25 to 37 beats per minutes, when breathing and restoring oxygen levels.
The fact that the heart rate is close to the maximum emphasizes why blue whales are susceptible to changes in their environment. The research carries important implications for the conservation and management of such endangered species. Blue whales have been declared endangered since 1970, and they are protected under both the Endangered Species Act and the Marine Mammal Protection Act.
The research has been published in the journal Proceedings of the National Academy of Sciences. The research paper is titled "Extreme bradycardia and tachycardia in the world’s largest animal."