Abstract

The North Atlantic right whale (Balaena glacialis) is a highly endangered species. Current estimates list the population at approximately 300 individuals. In addition, the calving interval has lengthened in recent years raising concern for the survival of this species. Approximately 60% of the animals have scars indicating either entanglements with ropes and/or nets or injuries from boat strikes. This species is highly vulnerable because they feed, migrate and reproduce in the coastal ocean waters along the eastern edge of the United States.

In most cases, entangled whales either break free on their own or are cut free by marine mammal rescue teams. Several cases have been documented where the entanglement could not be removed. The large size (20,000–45,000 kg) and strong-willed temperament preclude any physical handling of this species. Because of an experience with a fatally entangled female NA right whale in 1999, a group of biologists and veterinarians met to explore the potential for sedation of a free-swimming whale for disentanglement efforts.

On June 8, 2002, an adult male NA right whale (#1102) who later came to be known as “Churchill” was reported by a NOAA-SAS survey flight to be entangled northwest of Cultivator Shoal. An assessment team removed part of the entangled ¾-inch polypropylene rope and determined that a linear wound across the maxilla appeared to be infected. The whale apparently had a single line that entered one side of the mouth, cinched around the rostrum and exited the other side of the mouth. This line was cinched very tight and was imbedded in necrotic tissue in the head. The whale was in very bad condition. The inability to remove all of the rope and the condition of the wound indicated that the entanglement was life-threatening. A satellite telemetry buoy was attached to the end of the entangled rope to enable tracking and relocating the whale.

Available sedatives, analgesics and immobilization drugs were reviewed for the following characteristics: clinical use in related marine mammals, availability of a specific antagonist, predicted potency and deliverable concentration. Midazolam and meperidine were selected as the drugs that best fit these criteria.

Clinical experiences with these two drugs had demonstrated efficacy in a killer whale (Orcinus orca) at a dosage of 0.025 mg/kg midazolam and 0.25 mg/kg meperidine. Furthermore, this combination has been used routinely for sedation/immobilization of seals, sea lions and walruses. A benzodiazepine antagonist (flumazenil) was available. The solubility characteristics of midazolam suggested reformulation of the drug to approximately four times the commercially available 5.0 mg/ml concentration would be possible. However, when lyophilized, midazolam was redissolved in equal parts sterile water and ethyl alcohol; a final concentration of 90 mg/ml was then obtained. Commercially formulated meperidine (50 mg/ml) was lyophilized and redissolved in sterile water to a final concentration of 550 mg/ml. The opioid antagonist naltrexone was obtained for reversal of meperidine. Based on relative potency data of meperidine and carfentanil, the reversal dosage was estimated to be 1 mg of naltrexone for each 500 mg of meperidine.

On the first sedation attempt, only midazolam was administered in order to determine if sedation alone would be effective and safe for a free-swimming whale. As a starting point, the initial dosage was estimated by metabolic scaling. On June 26th, 500 mg midazolam was given IM. Thirty-seven minutes later, a second 500 mg midazolam dose was administered. No measurable sedation was observed from either dose.

The second attempt to sedate included both midazolam and meperidine. Since the metabolically scaled dosage produced no observable effects, the dosage of midazolam used to sedate a SeaWorld killer whale was used (0.025 mg/kg). Based on the estimated body weight of 40,000 kg, the midazolam dosage was estimated to be 1000 mg (1 g). However, limited capacity of the syringe dart resulted in a meperidine dosage of only 7500 mg (0.17 mg/kg). The two drugs were administered on July 14th. The signs of sedation included slower swimming and decreased swimming strength.

The final sedation attempt on August 30th utilized an increased dosage of meperidine. Additionally, the plan was to decrease the dosage intervals and increased number of dosages. A total of four doses of 1 g midazolam and 10 g of meperidine for a total of 40 g meperidine + 4 g midazolam were administered over a 2-h and 43-min period.

Greater sedation was apparent without full immobilization of the whale. Signs of sedation included a lower respiratory rate, slowed breeching and decreased swimming strength. Freeing Churchill from the rope required physical restraint as well as sedation. Attempts to place a harness around the tail of Churchill failed despite successful sedation. Ultimately, we were not able to remove the rope.

A method for drug administration of sedatives to a free-swimming whale was developed and successfully deployed. A blow-dart style syringe with a 12-inch long needle was designed and assembled by the engineering staff at Woods Hole Oceanographic Institute.

The design of the current syringe used for pharmacologic injections into large whales was adapted from designs used for large terrestrial mammals for remote drug delivery. All components for the main syringe are made of polycarbonate. This material was chosen for its impact resistance and its ability to be solvent welded together, thereby minimizing the cost of machining. The barrel is a piece of standard size tubing that is simply cut to length. Both the nosepiece and the tailpiece are machined from solid stock to fit the inside dimension of the barrel, and the plunger is machined for an O-ring seal to the inside dimension of the barrel. A check valve in the tail of the syringe was an “off the shelf” product, which has a polycarbonate body for easy assembly into the syringe.

The needle was a piece of type 316 stainless steel tubing that measures approximately 4.7 mm o.d. x 3.2 mm i.d. (3/16 o.d. x 1/8 i.d.). The tip was welded closed and then ground to a 15° bevel point. There was a 2.3-mm hole drilled through the tip approximately 21 mm from the point. The drug delivery outlet was sealed with Tygon or surgical tubing until the needle penetrated the whale’s skin. The stainless steel tube was welded to a ¼-20 socket head cap screw that has a 3.2-mm hole bored through the middle. This screw attached the needle to the syringe.

Churchill was followed for 100 days and three sedation procedures were performed. The dosage for light sedation using midazolam and meperidine was successfully determined for a large free-swimming whale. A method for drug delivery and a special, high-concentration drug was developed and deployed successfully.