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Entanglement in fishing gear is a known source of large whale injury and mortality. Although management initiatives can be implemented to reduce impacts, their effectiveness is difficult to evaluate from eye-witnessed entanglements alone. Furthermore, entanglement rates and impacts are not well-understood in most areas of the world.
The caudal peduncle and tail are commonly implicated in humpback whale, Megaptera novaeangliae, entanglements and consistently presented during the terminal dive. Since 1997, PCCS has studied scarring on free-ranging whales each year as a way of tracking entanglement rates. We developed systematic protocols which we use to study Gulf of Maine humpback whales across their feeding range. Our methods of scar interpretation have been successfully tested on whales with documented entanglements.
PCCS research indicates that more than half of the humpback whales in the Gulf of Maine exhibit scarring that was likely to have resulted from a prior entanglement. Scar acquisition rates indicate that an average of 12% of the population becomes entangled annually. Juveniles appear to be at highest risk, although whales continue to become entangled when mature. Fewer than 10% of the whales that acquire new entanglement injuries were actually seen and reported while entangled. See Robbins and Mattila (2004) or Robbins (2009) for further information.
Scar-based studies indicate that entanglement is a more frequent occurrence than observed cases would suggest. The most effective management initiatives are therefore those that focus on prevention, rather than intervention for witnessed events. Nevertheless, disentanglement can improve the outcome for individuals that are witnessed entangled and generates critical data for understanding and thereby preventing future events. Learn more about PCCS disentanglement efforts here.
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