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Large Whale Entanglements

The Threat

The primary threat to humpback whales and many marine animals is entanglement in lines and nets. The International Whaling Commission recently listed by-catch as a primary concern, and it has been estimated that over 300,000 cetaceans die each year worldwide as a result of entanglements (Reid et al, 2006). The sources of these entanglements are extensive and diverse. Actively fished gear, non-fishery-related gear, derelict fishing gear, constituting lost or abandoned gear, and other types of marine debris have been implicated in marine animal entanglements.  Since 2002, the Hawaiian Islands Humpback Whale National Marine Sanctuary has received more than 94 confirmed reports of entangled humpbacks, representing at least 65 different animals. However, the number of entanglements is certainly much greater since many entanglements go unreported.  Preliminary scar analysis of humpback whales in Hawaii suggests that around 22% of the population have been recently entangled (Robbins et al, 2007).  Scar analysis of humpbacks in northern Southeast Alaska indicated that around 50% of the population has been recently entangled (Neilson, 2006).

Entangled Humpback Whale
Hawaii Marine mammal Consortium/ NOAA MMHSRP (permit #932-1489)

The Impact

For many pinnipeds and small cetaceans, death is typically immediate, since drowning in the gear is usually the cause of death.  For large whales whose greater size allows them to pull gear towards the surface and even break away from all or parts of the entangling gear to return to the surface for air, this is generally not the case.  However, the risk of death, while not immediate, still exists if the animal remains entangled. Large whales may starve to death, experience physical trauma from the gear, develop infections resulting from wounds, and be susceptible to other threats like ship-strikes.  In addition, the impacts of entanglement may be non-lethal, as in the reduction of reproductive success.

Entangled humpback whale
HIHWNMS, MMHSRP Permit #932-1489

Neilson, J. 2006 Humpback Whale (Megaptera novaeangliae) entanglement in fishing gear in northern Southeast Alaska. Thesis. University of Alaska, Fairbanks.

Reid, A. J., P. Drinker, and S. Northridge. 2006. Bycatch of  marine mammals in U.S. and global fisheries. Conservation Biology. 20:163-169.

Robbins, J., Barlow, J., Burdin, A.M., Calambokidis, J., Gabriele, C., Clapham, P., Ford, J., LeDuc, R., Mattila, D.K., Quinn, T., Rojas-Bracho, L., Straley, J., Urban, J., Wade, P., Weller, D., Witteveen, B.H., Wynne, K. and Yamaguchi, M. 2007. Comparison of humpback whale entanglement across the North Pacific Ocean based on scar evidence. Unpublished report to the Scientific Committee of the International Whaling Commission.  Report number SC/59/BC.


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