Abstract

Two important human related mortality factors for the North Atlantic right whale include ship strikes and entanglement in fishing gear. The severity of entanglements for large whales may range from temporary gear involvement to death of the animal. Entanglement may include multiple line wraps and other net gear that can restrict mobility and result in strangulation of tissue such as the flippers, tail, and peduncle. Line and netting may also pass through the oral cavity encircling the maxilla and mandible with line caught between the baleen plates.

Standard disentanglement procedures for large whale gear removal includes highly trained personnel that utilize cutting tools to incise, remove and when possible retrieve gear and/or line. Some species of whales such as the humpback (Megaptera novaeangliae) are more prone to allow disentanglement teams to work in proximity to the head and may even temporarily cooperate by stopping during the activity. The right whale, by contrast, is behaviorally much different. Right whales with line and netting wrapped around the head usually avoid contact with disentanglement crews working near the head, making access for line removal difficult and in many cases impossible. These whales are unable to sustain themselves nutritionally, develop wounds that compromise them systemically, slowly deteriorate and usually die.

In the late 1990's, with little success on removal of head wraps, some of the authors with members of the disentanglement teams, investigated the development of a chemical restraint system for use on large whales.¹ Sedation drugs that had been successfully used for numerous cetacean species in oceanaria and zoos were initially utilized. However, the drugs were concentrated to make the administration volumes realistic. The first delivery approach was a cantilever system which required a long pole with specially designed darts attached to the end that were dropped onto the back of the animal. Initial drug dosages were scaled based on assumptions of possible metabolic size. After four partially successful attempts on an animal with a severe mouth wrap it was felt that the delivery system needed to change as well as further evaluation of alternative drugs. In response to NOAA and Woods Hole Oceanographic Institution, Pax Arms of New Zealand was contracted and developed a dart gun capable of delivering 57 mls. This system was initially field tested on blubber and muscle from stranded cetaceans. The system was then utilized in the field for the delivery of antibiotics to a mother-calf pair of humpback whales that traveled 100 miles up the Sacramento River resulting in severe skin deterioration.² In 2007 based on use in oceanaria, butorphanol demonstrated potential improvements over midazolam alone or the combination of meperidine with midazolam and may be better suited for future sedation attempts.^{3, 4} The primary improvement was less likelihood of the whale over-riding sedation and improved approachability of the whale while sedated. Ideal sedation effects would allow a disentanglement crew to approach the head with minimal reaction from the animal, cause minimal changes in respiratory quality or rate, and reduce swimming speed while having the animal surface normally.

In January 2008 a severely entangled right whale was identified off the Georgia coast. The Georgia Department of Natural Resources disentanglement team on initial contact was able to remove a large amount of trailing line and attach a tracking transmitter. In late January an attempt was made to sedate the individual with a low dose of butorphanol and midazolam. The first attempt did not produce adequate sedation. Afterwards the animal was not available for another sedation attempt for almost 6 weeks. To minimize volume concerns and drug interaction, butorphanol HCl and midazolam HCl were purchased from ZooPharm Inc. since both drugs from this supplier were compatible when mixed together in the syringe darts. On March 5, 2009 the animal was again approached by the sedation team and the administered dose was doubled from the original attempt 6 weeks before. The first darting attempt was from a caudal perspective and the dart entered at a flat angle. After 30 minutes there were some changes in respiratory quality and rate but the whale did not allow the disentanglement team to approach the head and veered away from the boat approach as before. The following day the dose was increased by 50% to 0.1 mg/kg of butorphanol and 0.1 mg/kg of midazolam. Two darts were well placed at the desired angle and thirty minutes later the disentanglement boat approached the animal with a notable difference in its reaction. The whale was surfacing with the disentanglement boat near the head and not turning away. This allowed the crew to cut free a large portion of the line and to use a hand tossed grapple to aid in retrieval of the gear. The whale also allowed close approximation of the larger dart boat for skin biopsies and health assessment photos where previously it had not cooperated. Two plus hours after sedation the animal was swimming and surfacing well so it was decided not to reverse the drugs with opioid or benzodiazepine antagonist. The use of antagonists will remain an option in future trials since the true half life of these drugs in this species is unknown at this time.

Acknowledgements

The authors would like to thank their partners in the disentanglement program, Clay George, Mark Dodd, and Kate Sparks from Georgia DNR, Tom Pitchford and Katie Jackson from Florida FWC Right Whale Program, Barb Zoodsma, the NOAA Southeast Region Right Whale Coordinator, Chris Slay from Coastwise Consulting, the Northeast Disentanglement Group, including David Morin of NOAA, Scott Landry and Brian Sharp of Provincetown Center for Coastal Studies, Woods Hole Oceanographic Institution, The Wildlife Trust and FWC for valuable flying and coordinating skills, the Marine Mammal Health and Stranding Response Program at NOAA, the University of Wisconsin College of Veterinary Medicine pharmacy, and ZooPharm Inc. This work was performed under permit 932-1489 with NOAA Fisheries and financially supported by NOAA Fisheries and in part by the Aquatic Animal Health Program at the University of Florida through a grant from the Florida Fish and Wildlife Commission.

References

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