marine mammals

Baleen Whale Cortisol Levels Reveal a Physiological Response to 20th Century Whaling

Today I learned: whaling in the 20th century indirectly stressed out many different species of whales. A group of scientists looked at the earplugs of three different types of baleen whales: fin, humpback, and blue. A whale earplug is a collection of ear wax that has alternating lines that tell the age of a whale (like tree rings do) and store both endogenous (i.e. hormones) or exogenous (i.e. pollutants) chemicals. Because of this, they could measure the amount of cortisol, a stress hormone, in each whale during many different years. They found that when whaling numbers peaked, there was also a peak in the average cortisol levels. Interestingly, when whaling decreased during World War II, they still saw slightly higher cortisol levels, which suggests that wartime noises (i.e. submarines, bombing/explosions, planes, etc.) also increased the stress in the whales. The sharp drop in cortisol levels in the 1970s was connected to the start of the Marine Mammal Protection Act that put a moratorium on whaling. However, cortisol levels have been slowing increasing since then, indicating that other stressors are present (i.e. increased sea temperatures, over-fishing, and noise).

Graph showing that when whaling numbers peak, there is a peak in cortisol levels

The graph shows that from 1900-2000, when whaling numbers (blue) increased, there was also an increase in cortisol levels (black). Highlighted in grey is a period corresponding to WWII where the whaling numbers were low, but cortisol was still high. Also shown is a red line to indicate when the Marine Mammal Protection Act went into effect in 1972 to emphasize the sharp drop in cortisol levels that followed.

Reference: Trumble, Stephen J., et al. “Baleen Whale Cortisol Levels Reveal a Physiological Response to 20th Century Whaling.” Nature Communications, vol. 9, no. 1, 2018, doi:10.1038/s41467-018-07044-w.


War of the Whales by Joshua Horwitz

An unusually large whale stranding event in the Bahamas on March 15, 2000, set into motion a clash between environmental activists and the US Navy. War of the Whales, part detective and part history novel, by Joshua Horwitz covers every nuance of this battle, while also providing some really cool marine animals facts throughout. As someone who toyed with becoming a marine biologist, until realizing that a fear of open water and studying marine animals don’t really mix, this book was right up my alley. Right off the bat, you get to learn that beaked whales are the only predator that regularly dive one mile deep; with one dive even being recorded at two miles deep for just over two hours. Even if you don’t have a lot of background knowledge on these topics, this book is super easy to read, largely due to Horwitz’s writing style. War of the Whales skillfully avoids being a dry listing of facts thanks to its well-written and compelling narrative that spans across a decade or so of back-and-forth between activists and the US Navy, along with brief ‘flashbacks’ to give the historical context that led up to the current events. So, for anyone who is even mildly interested in the ocean or the interplay between ocean conservation and military policy/practices, this book a great choice.

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