Marine traffic is increasing worldwide, and where ships and whales overlap, collisions between the two are inevitable, writes Frank Swain for an article published in Hakai Magazine.
Where is the problem acute?
The problem is particularly acute in the Canary Islands, off the northwest coast of Africa, an area that teems with both whales and large ships.
Marina Arregui, a biologist at Spain’s University of Las Palmas de Gran Canaria said, “There are many high-speed ferries in the Canary Islands, and we’ve seen an increase in stranded whales with signs of ship collision.”
However, determining whether these collisions caused the deaths of the whales is not straightforward.
When a whale dies!
While some types of whales sink when they die, others float. Some particularly buoyant species, such as sperm whales, can take weeks to wash ashore, often arriving in advanced states of decomposition.
Even when ship strike injuries are apparent—such as deep cuts made by the keel of a ship—it’s possible these wounds were inflicted postmortem, while the carcass drifted at sea.
Ship strike killed a whale?
Lung tissue samples
To determine whether a ship strike killed a whale, Arregui and her team examined preserved lung tissue samples collected from 24 sperm whales that had died near the Canary Islands between 2000 and 2017.
Sixteen of the whales had injuries consistent with ship strikes, while eight were examined to serve as a control group.
Lumps of misplaced fat
Arregui and her team examined the tissues, looking for small lumps of misplaced fat. When an animal suffers a major injury, fat cells from damaged tissue enter the bloodstream. The circulatory system carries these lumps around the body until they become tangled in fine blood vessels, such as those in the lungs. This is known as an embolism.
Presence of clumps of fat cells in lungs
Because these clumps of fat cells can only be transported around the body while the whale’s heart is beating, their presence in the lungs indicates the animal was still alive when the trauma occurred.
What does fat emboli say?
In the crime lab, these fat emboli indicate someone was a victim of trauma before they died. Arregui says this is the first time the technique has been performed on whales, although it’s been used in animal pathology before.
Size of fat emboli
Of the 16 whales that had injuries associated with ship strikes, 13 had fat emboli in their lungs. The scientists also examined the eight whales in the control group and found that two had small numbers of fat emboli, likely the consequence of small, non-fatal injuries.
Whale conservation campaigners
Armed with better diagnostics, whale conservation campaigners will be able to more convincingly argue that mitigation measures are needed to protect whales.
James Robbins, a doctoral candidate at the University of Portsmouth in England who wasn’t involved in the study said, “There is little understanding of how frequently ship strikes happen. Being able to say this animal was killed by a ship could prove very useful for getting closer to the true number of animals affected.”
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Source: Hakai Magazine
