Scar-Based Inference Into Gulf of Maine Humpback Whale Entanglement: 2007

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. In 2007, a total of 794 images were obtained of the caudal peduncle and flukes of 289 individual humpback whales in the Gulf of Maine. Preferred photographs were obtained while parallel to the whale and slightly ahead of its flukes during the terminal dive. Suitable quality images were examined for evidence of wrapping scars, notches and other injuries that were believed to be entanglement-related. The vast majority (87.5%) of individuals involved in prior documented entanglements between 1985 and 2006 were successfully scored as having a high probability of prior entanglement. Overall, 9.4 ± 5.84% of individuals sampled in 2007 exhibited new high probability scarring relative to 2006. Similarly, 6.6 ± 2.86% (n=19) of the total 2007 sample exhibited unhealed injuries that were likely received within the past year. Neither finding was significantly different from 2006, and there were no significant differences in entanglement frequency among the Gulf of Maine areas studied in 2007. However, juveniles continue to be more likely than adults to acquire new injuries. A total of 27 acquisition events were documented in 2007, bringing the number detected by scar analysis alone to 291 events since 1997, or an average of 26.5 events per year of the study. However, none of the events inferred from 2007 scarring were reported in progress. Overall, scar-based monitoring continues to achieve large samples with which to evaluate entanglement rates on an annual basis. The use of mark-recapture statistical modeling techniques, already in progress, is expected to further enhance the inference possible from these data. This study is expected to play an important role in evaluating the effectiveness of planned coast-wide ground line modifications in 2009. 2008 Contract no. EA133F07SE2932 NMFS (National Marine Fisheries Service) NEFSC (Northeast Fisheries Science Center) Submitted Public Domain 1861