Assessing post-release success of rehabilitated odontocete cetaceans
Important questions have been raised regarding the relative risks and benefits of rehabilitating and releasing stranded odontocete cetaceans, but until recently few data have been available to support an appropriate evaluation.
In the early years of cetacean rehabilitation, success in getting the animals to the point of release was infrequent, but success rates have improved markedly in recent years thanks to increased experience and knowledge and improved diagnostics and facilities.
Concurrently, safe and practical techniques for monitoring rehabilitated cetaceans post-release have become available, especially involving radio telemetry, providing the potential for assessing the success of the animals released back into the wild. Decreased tag size and increased experience with attachments lasting for periods of months have helped to allay concerns about safety risks from the tags themselves.
Recognizing that rehabilitation can be a very expensive undertaking, requiring extended allocations of limited medical, facility, and staff resources, increasing effort has been made in recent years to monitor rehabilitated cetaceans post-release in order to be able to evaluate the success of the treatments.
With support of the NOAA John H. Prescott grants program and collaborative efforts involving Dr. Forrest Townsend, Dr. Frances Gulland, and Rob DiGiovanni, we engaged in a systematic review of post-release success relative to initial cause of stranding, aspects of rehabilitation, treatments, or life history parameters.
We compiled and reviewed 69 cases from 1986-2010 involving 10 species of small odontocete cetaceans.
Of these, 41 cases involved single strandings or rescues, while 28 of the cases involved mass strandings. Thirteen of the bottlenose dolphin cases and all 38 of the cases involving other species were strandings with subsequent rehabilitation efforts. Eighteen bottlenose dolphin cases were rescue captures brought about by entanglement, out-of-habitat, or maternal death situations. Seven of these interventions led to rehabilitation, while the remaining 11 rescues involved on-site examination, treatment if necessary, and release without rehabilitation.
A final report for this review is currently being prepared. Among the preliminary findings is a definition for release success: following release, the cetacean exhibits ranging patterns, habitat use, locomotion, behavior, and social interactions typical for the species, stock or individual, and/or at least does not exhibit abnormal behavior, for a minimum of six weeks. Not all of these data will be available in all cases. To obtain these data, direct visual observations are best, but in the absence of observations, some of these data may need to be inferred from radio-telemetry.
Based on this criterion, 80% of cases were identified as successful or unknown but likely to have been successful. In general, interventions prior to stranding led to higher success rates than did stranding with rehabilitation. Mass stranded individuals demonstrated greater success than single stranders. Young calves without their mothers, old animals, and animals with hearing deficiencies exhibited poor success post-release. In all cases, the importance of post-release monitoring was noted.
