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Humpback whale. Image: Christopher Swann

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Size does matter for entangled whales but study finds that bigger is not necessarily stronger

Humpback whale with entanglement

Entanglements in fishing gear may be one of the single largest threats faced by whales and dolphins globally.  Referred to as “bycatch” because these interactions are incidental, not intentional, these interactions number in the hundreds of thousands each year. While some whales and dolphins escape with only scars as evidence, including all nine of WDC’s Whale Adoption Project humpbacks, an unknown number drown, starve to death, or die from a resulting systemic infection as the gear literally saws into their flesh. The risk of any single piece of fishing gear entangling a whale or dolphin is low but the risk of a whale or dolphin becoming entangled is high. For critically endangered species like the North Atlantic right whale or the vaquita, accidentally blundering into fishing gear brings can bring them one step closer to extinction.  

As part of several United States federally appointed Take Reduction Teams, WDC is working to create measures that reduce the risk of entanglements.  However, to create management plans that are effective, it is important to better understand the risk.  A recent study by researchers at the University of North Carolina, Wilmington and the Smithsonian Institute have looked at whale bones from museums and stranded species to measure just how much force a whale’s tail needs to pull the individual out of entangling gear.  The surprising results show that strength is not necessarily proportional to size.  Understanding that larger whales are not necessarily stronger than their smaller counterparts is enormously important when considering the breaking strength of lines used in various types of fishing industries. 

Although these data are invaluable, it is important to remember that entanglements involve living whales and dolphins so behavior is also a significant factor to consider.  It appears that, at least in some cases, whales will actually roll into the gear, rather than pull away from it.  Taking this “path of least resistance” may make sense to the whale at the time by reducing the pressure they feel from the gear, but it ultimately exacerbates the entanglement.  In that case, even a relatively weak piece of line can be fatal. 

There is no simple answer to this complex problem but data like those presented in this study provide valuable insight. 

If you’d like to help our work to reduce the threat of bycatch to whales and dolphins, please consider adopting one of our “survivors”.  As always, thank you for helping us work toward a world where every whale and dolphin is safe and free.  

About Regina Asmutis-silvia

Executive director - WDC North America