Legislation effective in 1990 prohibits driftnetting for swordfish or thresher shark within 75 miles of the mainland from February 1 through July 14 to conserve the thresher shark resource. The Marine Mammal Protection Act mandated observer coverage on driftnet vessels since 1989. This rule followed the first year of a test of the effectiveness of pingers in reducing interactions with marine mammals. The study, funded in part by California swordfish fishermen and carried out and monitored by federal observers, successfully reduced interactions with cetaceans by 75 percent. The use of pingers is helping California's swordfish fleet meet the stringent requirements of the Marine Mammal Protection Act to reduce interactions to rate near zero.
Foreign nets drift on the surface, where most marine mammal and seabird entanglement occurs.
Acoustic pingers are deployed on all California swordfish-shark driftnets. Observer reports indicate that California's driftnet fishery has a minimal impact on sealife.