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Description:Entanglement in fishing gear is a known source of humpback whale, Megaptera novaeangliae, injury and mortality. However, reported 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 injuries have been studied annually as an index of entanglement frequency. Here we report on the analysis of injuries at the caudal peduncle and fluke insertion of 335 individual Gulf of Maine humpback whales in 2010 and compare those results to previous years. We focus particularly on evidence for change since the 2009 federal sinking ground line rule, which was intended to reduce the amount of line in the water column. 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 in 2010 with comparable photographic coverage in 2009 (n=130), 16.9% ± 6.45% exhibited new scarring. Similarly, 13.5% ± 3.8% of 319 individuals with adequate coverage in 2010 exhibited unhealed injuries likely obtained within the prior year. In both metrics, juveniles exhibited a higher frequency of new injuries than adults. Multi-state statistical models were further used to study patterns and implications of entanglement injury acquisition. Modeling was based on individuals sampled Gulf of Maine-wide, 1997-2010. It included 2,012 annual encounters of 527 adults (279 females, 248 males) and 1063 encounters of 713 known or suspected juveniles. Modeling results through 2010 continue to indicate that juveniles have a higher annual probability of acquiring new injuries than adults. The model averaged probability of an individual acquiring new injuries between 2009 and 2010 was 0.302 (95%CI: 0.200-0.429) for juveniles, 0.103 (95%CI: 0.076-0.139) for adult females and 0.105 (95%CI: 0.076-0.141) for adult males. Results to date do not indicate a decline in entanglement rate immediately following the coast-wide federal requirement for sinking ground line, but they also do not exclude possible effects. Available data were limited to one full feeding season after the ground line rule and so additional work will be needed to fully assess the effects of mandatory changes in fishing practices aimed at reducing entanglement rates.
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