Effectiveness of Mitigation to Reduce Entanglement Impacts on Humpback Whales in the Gulf of Maine

Humpback whales in the Gulf of Maine (GOM) are vulnerable to injury and mortality from human activities, including from entanglement in fishing gear. Over the past decade, two major changes were mandated to commercial fishing practices along the U.S. East Coast to reduce entanglement frequency. Federal rules in 2009 and 2015 reduced the profile of ground line and the number of vertical lines in the water column, respectively. We used data on population abundance and survival from 2000 through 2016 as a basis for evaluating the effectiveness of these initiatives. We focused on a subset of observed entanglement cases that we assessed as having a high probability of involving GOM humpback whales and relevant fisheries. The number of observed events was lowest in 2013 and 2014, but as high in 2016 as in any pre-rule year. There was no correlation between the number of reported events and estimated GOM humpback whale population size, nor between the per capita entanglement report frequency and mitigation periods. A Bayesian state-space mark-recapture model did not suggest improvements in population survival rates after the Ground Line Rule. An estimated increase in survival from 2015 to 2016 may have been related to the Vertical Line Rule or other factors. Continued research will be necessary to evaluate the effectiveness of the Vertical Line Rule for reducing entanglement impacts on Gulf of Maine humpback whales. 2018 Contract EE133F-17-SE-1320, Task II NMFS (National Marine Fisheries Service) NEFSC (Northeast Fisheries Science Center) Submitted Public Domain 1930