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Entanglement in fishing gear is a serious source of large whale injury and mortality in the Gulf of Maine. Although management initiatives have been implemented to address this impact, their effectiveness is difficult to evaluate due to limitations and biases in the detection of entanglement events.
The caudal peduncle is commonly implicated in humpback whale entanglements and is consistently presented during the terminal dive. Since 1997, PCCS has monitored the caudal peduncle of free-ranging humpback whales, Megaptera novaeangliae, for evidence of entanglement-related scarring. Photographs of the caudal peduncle are obtained while parallel to the whale and slightly ahead of its flukes during the terminal dive. Images are coded to reflect the presence or absence of wrapping scars, notches and other injuries that were believed to be entanglement-related. Study assumptions have been successfully tested against whales with documented entanglements.
Each year, between 48% and 65% of the humpbacks sampled exhibit scarring that was likely to have resulted at some point in their lifetime. Scar acquisition rates suggest that 10-25% of the population becomes entangled each year. Juveniles appear to be at highest risk, although whales continued to become entangled when mature. Females exhibiting evidence of a prior entanglement produced significantly fewer calves during the study period than did females with no evidence of a prior entanglement.
Between 1997 and 1999, at least 31 Gulf of Maine whales were likely to have been entangled, in addition to the 12 confirmed entanglements that were reported during that period. These results indicate that entanglement is a more frequent occurrence in the Gulf of Maine than previously suspected. Given the low rate at which these events have been reported (3%), the most effective management initiatives are likely to be those that focus on prevention, rather than human intervention (disentanglement).
Robbins, Jooke and David K. Mattila. 2001. Monitoring entanglements of humpback whales (Megaptera novaeangliae) in the Gulf of Maine on the basis of caudal peduncle scarring. Unpublished report to the 53rd Scientific Committee Meeting of the International Whaling Commission. Hammersmith, London. Document # SC/53/NAH25. Do not cite without permission from the first author.
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