Effects of rearing methods on survival of released free-ranging juvenile southern sea otters

Abstract Since 1984, Monterey Bay Aquarium’s Sea Otter Research and Conservation (SORAC) program has treated more than 70 stranded newborn sea otter pups. Pups rehabilitated for release have been reared by methods that rely heavily on human care, contributing to release failures. From 1986 to 2000, sixty-seven percent (67%) of unsuccessful pup releases resulted from failures to reintegrate with the wild population and avoid interactions with humans. To address these failures, SORAC initiated a sea otter surrogate program, pairing stranded pups with captive adult females that adopt pups as their own. We predicted that pups reared by surrogate females ( n  = 5, 2001–2002) would develop foraging skills at a younger age, and would have greater success re-acclimating to the wild compared with pups rehabilitated by traditional methods ( n  = 6, 1998–2000). Results indicated that surrogate-reared pups began foraging independently on live-prey 2–3 weeks earlier, and had greater survival rates (71% vs. 31%) in the wild than pups reared without surrogates. The surrogate program, therefore, was less labor-intensive and more effective than traditional rehabilitation methods. In addition to these practical advantages, the surrogate program may also benefit research and conservation objectives for southern sea otters by providing means to (1) better understand pup behavioral and physiological development, (2) measure energetic costs of rearing pups to indicate why survival rate of prime-aged females is declining, (3) improve techniques to reintroduce sea otters in the event of a catastrophic decline in the wild population, and (4) engage and educate the public regarding threats to sea otters and their near-shore marine environment.