The authors conducted field studies off the coast of Iceland to measure the response of humpback whales (Megaptera noveangliae) in their feeding grounds to a whale pinger and seal scarer (acoustic deterrents). Results indicate that whale pingers caused a significant increase in humpback swimming speed and a significant decrease in surface feeding, and that seal scarers caused no significant, consistent behavioral changes. Additionally, the authors conducted a field trial of whale pingers on a capelin purse seine; the pingers did usually deter whales from the purse seine, and the two times that whales entered the net, the pingers combined with crew responsiveness seemed to aid their escape. Whale pingers can be a useful humpback whale entanglement mitigation tool, but they should be used only short-term so as to avoid reduced fitness consequences.