The bends are a type of decompression sickness associated primarily with divers using a compressed air tank. As the regulator delivers air at ambient pressure, the more pressure increases with depth, the more inhaled gases such as nitrogen dissolve in the blood. The concentration of nitrogen in the blood is thus much greater than at the surface. If the diver surfaces too quickly, the nitrogen, which can only be evacuated by the lungs, cannot return to these organs quickly enough. This forms nitrogen bubbles in the body tissues, which can lead to a number of injuries and trauma. It was once thought that such incidents were not a concern for free divers, as there is no exchange of air under water given that they dive with one breath taken at the surface. However, it has been demonstrated that the latter, depending on their dive time, depth and time spent at the surface, could also suffer certain injuries related to the bends.

Marine mammals, being champion divers, have morphological, physiological and behavioural adaptations not only to reduce nitrogen accumulation in their tissues, but also to manage nitrogen that has accumulated. Despite these adaptations, some individuals may experience diving accidents following stress. Whales react to that stress by altering their dive profile (time and depth) causing excessive oversaturation of tissues and the formation of nitrogen bubbles. This stress can be anthropogenic like the use of sonar or seismic activities that produce powerful sounds in the marine environment.

In 2002, a stranding of bottlenose whales in the Canary Islands coincided with military sonar tests conducted in the region. In a 2004 study, sperm whale skeletons showed holed and eroded bones, a typical indication of osteonecrosis, a chronic illness found in free divers over the long term. This disease is caused by repeatedly poor management of dive patterns, causing the formation of nitrogen bubbles in the body.

Researchers from the University of North Carolina Wilmington studied adipose tissue in the jaws of toothed whales. These tissues, which are used in echolocation, are known to absorb significant quantities of nitrogen. Depending on the type of fatty matter and the depth of the animal’s dive, researchers would be able to measure which species are most prone to diving accidents. The more fatty material absorbs nitrogen, the more the species is at risk. Their results were published in August 2015 in the Journal of Experimental Biology. Much research remains to be conducted to shed further light on this still mysterious issue.

To learn more:

Adipose tissue in the jaw

What are the bends?

Sperm whales and the bends

Whale Q&A - 9/9/2015

Camille Bégin Marchand

Camille Bégin Marchand has been employed for GREMM from 2013 to 2018. Although she began as a naturalist at the Marine Mammal Interpretation Centre, Camille’s interest in scientific writing would later land her a position on the Whales Online editorial team. With a passion for biology and a deep affection for the region, she is also pursuing a Master’s degree in forest sciences in collaboration with the Tadoussac Bird Observatory (OOT).

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