Scar-Based Inference Into Gulf of Maine Humpback Whale Entanglement: 2008

Entanglement in fishing gear is a known source of humpback whale, Megaptera novaeangliae, injury and mortality. However, eye-witnessed events provide limited insight into entanglement frequency, risk factors and biological impacts. The caudal peduncle is commonly implicated in humpback whale entanglements and is consistently presented during the terminal dive. Since 1997, peduncle scarring has been studied annually as a relative index of entanglement frequency. This study focused on images of the caudal peduncle and fluke insertion of 341 individual humpback whales sampled in the Gulf of Maine in 2008. Preferred photographs were obtained while parallel to the whale and slightly ahead of its flukes during the terminal dive. Suitable images were examined for evidence of wrapping scars, notches and other injuries observed in documented entanglements. Of the individuals with comparable photographic coverage in 2007 (n=120), 8.3% ± 4.95% exhibited new scarring in 2008. Using another metric, 10.3% ± 3.99% of 223 individuals with suitable coverage exhibited unhealed injuries likely obtained within the prior year. Neither approach suggested a change in entanglement rate from 2007. However, unhealed injuries provided greater insight into the higher annual frequency of entanglement among juveniles (20.8% ± 9.06%) versus adults (4.8% ± 3.47%), which may be important for tracking future changes in entanglement rate over time. Injuries documented in 2008 represented at least 23 recent events, in addition to those documented by eye-witness observers. Three events inferred from scarring were matched to entanglements reported in progress, indicating a successful entanglement reporting rate of 11.5%. Overall, scar-based inference suggested substantially more entanglement cases and associated deaths in 2008 than were actually witnessed. In the future, scar-based monitoring will provide a basis for evaluating the effect of recent coast-wide changes in fishing practices on humpback whale entanglement rates. 2010 Contract no. EA133F09CN0253 NMFS (National Marine Fisheries Service) NEFSC (Northeast Fisheries Science Center) Submitted Public Domain 1861