Post-release follow-up monitoring of stranded or injured dolphins

Dec 21, 2010 No comments By


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.

Follow-up monitoring graph

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.

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About the author

Randall Wells, PhD, is the Director of the Chicago Zoological Society’s Sarasota Dolphin Research Program (SDRP). He began studying bottlenose dolphins in Sarasota as a high school volunteer at Mote Marine Laboratory in 1970. He received his BA in Zoology from the University of South Florida in 1975, a Master’s in Zoology from the University of Florida in 1978, a PhD in Biology from the University of California, Santa Cruz in 1986, and a Post-doctoral Fellowship in Biology from the Woods Hole Oceanographic Institution in 1987. Employed by the Chicago Zoological Society since 1989, he is a Senior Conservation Scientist, and in this capacity he also manages Mote Marine Laboratory’s Dolphin Research Program. As a Professor of Ocean Sciences (adjunct) at the University of California, Santa Cruz, he serves as major advisor for MS and PhD students, and he is an adjunct Professor with the University of North Carolina, Wilmington, Duke University, and the University of Florida’s College of Veterinary Medicine. Wells was President of the Society for Marine Mammalogy (2010-2012).
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