Abstract
On July 14, 2009, a juvenile male pilot whale (Globicephala macrorhynchus) stranded on the beach in Curacao, Netherlands Antilles. Under the supervision of Southern Caribbean Cetacean Network (SCCN) and with the support and cooperation of the Curacao Sea Aquarium, Dolphin Academy, and Curacao Dolphin Therapy Center and the dedication of dozens of volunteer caregivers this pilot whale survived the stranding, regained his health, experienced two release-to-wild attempts, and now resides at SeaWorld of California.
The juvenile whale (estimated to be 300 kg) first appeared weak, emaciated, and disoriented, and needed to be held up in the water column to prevent drowning. The initial physical examination and blood work indicated profound malnutrition and dehydration, necessitating intubations of four liters of water every 2–3 hours. Within 12 hours he appeared stronger and even began consuming fish voluntarily. By day three his demeanor and appetite waned. At the site of a previous phlebotomy and running distally to the top of the fluke were multiple raised and ulcerated lesions radiating out from the central fluke vein. A culture was taken from one of the lesions and Amikacin was instituted at 12 mg/kg IM SID. Within two days his appetite and attitude picked up and the phlebitis lesion began to improve. Staphylococcus aureus was identified with sensitivity to Amikacin, among several other antibiotics. Once the lesions quieted, he improved quickly and over the next two months his strength and physique returned to normal.
In order to increase his strength and stamina to prepare him for release back to the wild, he was trained to follow a boat into the open ocean at least 4–5 km at top speeds of 20–25 knots once daily. After three months of training his aerobic capacity was developed to the extent that two separate attempts were made for release, and both failed. On the second attempt he was led into a pod of conspecifics nearly 35 km from the rehabilitation site. For nearly about ninety minutes he swam among the whales occasionally diving for long periods of time, but at the moment the others sounded he returned to the boat.
Why did this pilot whale not integrate back into the wild? Was the pod not a familiar one? Were the other whales not accepting him? Had he become too accustomed to human care? Was he too young to be independent of a mother? Although we can never know for certain there is strong evidence to support the theory that his hearing was impaired and may have been insufficient to allow him to feed naturally, or perhaps even communicate properly.
Although the whale could navigate through turbid waters in his enclosure and the surrounding bay, track a boat in the open ocean at great distances, and track fish thrown into his pool more than 25 meters away in complete darkness while producing audible click trains, the possibility that he had lost some of his hearing needed to be investigated. A single Auditory Evoked Potential test performed two months after his stranding indicated that he was unable to hear sounds above 10 kHz.1 A second test was performed by a team of auditory experts from the U.S. Navy after he had been successfully transported to SeaWorld of California verified the first results but found hearing impairment above 20 kHz (normal for a pilot whale appears to be best at 40 kHz with an upper limit between 80–100 kHz).2
There is a remote possibility that Amikacin therapy produced this selective hearing loss as has been demonstrated in both humans and cetaceans.3,4 While drug administration cannot be ruled out as a cause of hearing loss, dolphins that showed hearing loss were treated with similar drug dosages as other animals that did not show hearing deficits. In one study hearing tests were conducted both before and after drug treatment with five Risso's dolphins, and showed no effect on hearing.1 Fortunately, in one case of ototoxicity caused by aminoglycoside therapy hearing returned after a period of time (Ridgway, personal communication). Although it remains a remote possibility that Amikacin contributed to his hearing deficits, follow-up tests are scheduled for the near future.
In the authors' opinion, a more plausible scenario is congenital or postnatal hearing loss that rendered him ineffective at foraging independent of his mother's milk. Delphinids at his relative age are either fully weaned or in the later stages of weaning and should have long since developed foraging and feeding skills independent of their mother. Based on his body condition at the time of stranding his caloric needs were clearing not being met, thus suggesting that hearing loss may have contributed to his inability to feed himself. Even though it seemed evident this pilot whale had at least some degree of echolocation skills, it is unlikely that this animal could have foraged or socialized naturally considering the degree of hearing loss.
Acknowledgements
The authors would like to acknowledge the effort of the Southern Caribbean Cetacean Network (SCCN), the team of trainers from the Dolphin Academy and Curacao Dolphin Therapy and Research Center, Adriaan Schier (Dutch), the owners and staff of Zanzibar Restaurant (site of the make-shift rehabilitation facility), and countless volunteers who helped in the rehabilitation of "Sully," the pilot whale. Furthermore, we thank Paul Hoetjes, Eric Newton, and John Reynolds for their insights and valuable assistance in obtaining permits for the efforts in Curacao and the United States. Lastly, we want to thank Brad Andrews, Dr. Jim McBain, and Keith Yip from SeaWorld Adventure Parks for providing safe transport and home for this beloved whale.
References
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