Beginning in 1970, DeFran began a professorship in the Psychology Department at SDSU. Later, he worked with the Southwest Fisheries Science Center in La Jolla, CA, assuming responsibility for an ongoing boat-based photo-ID project designed to assess the population size and range characteristics of bottlenose dolphins in north San Diego County. Since 1984, Defran has conducted, and directed the Cetacean Behavior Laboratory’s dolphin population studies along the Southern California and Baja California Norte’s Pacific Ocean coastline, in the coastal waters of Belize, within Florida’s Indian River Lagoon, in the estuarine and coastal waters near Charleston, SC, and more recently, in the coastal waters of Guadalcanal in the Solomon Islands.