Expanding populations of marine mammals are posing challenges for fishery managers (increased predation on salmon) and harbor managers (human/animal use conflicts and structural damage). At the request of the Pacific Salmon Commission in Canada, a non-lethal deterrence array was evaluated at the Vancouver, B.C. Aquarium. Two captive harbor seals were acclimated and then exposed to the non-lethal field of pulsed DC at gradually increasing levels. The tests depicted in this video are the first known trials to determine the threshold responses of pinnipeds to a field of underwater electric current. As evidenced by their behavioral changes, harbor seals were extremely sensitive to a very mild voltage gradient that human observers could barely detect during hand immersions. The first seal was deterred 4 of 4 times while the second animal was deterred in each of 18 trials. This preliminary research has provided unique insights for marine mammal control technologies for possible use in the field.