Post-release follow-up monitoring of stranded or injured dolphins
By Randall Wells, PhD, Chicago Zoological Society
Understanding the fates of dolphins returned to the wild following rescue, stranding, and rehabilitation is crucial to evaluating the effectiveness of treatments and knowing what should be done in the best interests of the sick or injured animals. Over the past two years, we have received grants from NOAA’s J.H. Prescott Marine Mammal Rescue Assistance Grant Program to: 1) compile and evaluate cases of rescue or rehab and release where follow-up monitoring occurred, and 2) to provide follow-up monitoring services to cetacean rehabilitation facilities in Florida.
The proportion of released dolphins with which contact was maintained during each week post-release. Note the leveling- off after the sixth week, suggesting a high probability for longer-term survival if they survived the first six weeks.
The investigative team, including Dr. Forrest Townsend, Dr. Frances Gulland, Dr. Deb Fauquier, and Rob DiGiovanni, is evaluating 63 release cases, 31 involving bottlenose dolphins, and 32 involving Risso’s dolphins, rough-toothed dolphins, short-finned pilot whales, common dolphins, harbor porpoises, and a pygmy sperm whale. Initial findings suggest that released animals that survive at least six weeks have a high probability of longer-term survival (see graph). This is a conservative estimate of how much time should pass before a rehab/release case could be declared a success, because it is influenced by premature tag failure as well as animal deaths. Not surprisingly, those animals that are able to be rescued, treated and released in the field without requiring rehabilitation and without stranding demonstrate a higher survivorship than do dolphins that come ashore or require lengthy periods of treatment.
For their 2010 NOAA’s J.H. Prescott Marine Mammal Rescue Assistance Grant, the SDRP team is prepared to tag rehab dolphins with two kinds of tags. The first is a small VHF transmitter for direct radio-tracking, to facilitate observations of behavior and body condition. The second is a small satellite-linked tag with time-depth recording capabilities (STDR) to provide remote tracking options, with information provided on dive depth and duration. No cases requiring tagging and post-release monitoring have occurred in Florida since the beginning of the grant in September 2010.
