1Miami Seaquarium, Miami, FL, USA; 2Division of Comparative Pathology, Department of Pathology, University of Miami, Miami, FL, USA; 3Department of Neurological Surgery, University of Miami, Miami, FL, USA; 4Avian and Exotic Animal Medical Center, Miami, FL, USA
All four existing species of the order Sirenia are endangered. The fifth, Steller’s sea cow (Hydrodamalis stelleri), became extinct 27 years after it was discovered in the eighteenth century.1 In 1999 the manatee mortality in Florida was 268. The highest total number of deaths in a single year except for the red tide epizootic of 1996. Entanglement is the second most common traumatic injury in the Florida manatee.2 Entanglements present as crab trap, monofilament, or other debris on the flipper, head or body of the manatee. Some entanglements, such as acute crab traps, can be removed in the field. A recent recommendation by oceanaria is to do a full diagnostic work up on monofilament line entanglements, to ensure that line does not remain. The severity of the wounds varies from soft tissue damage, to varying degrees of bony involvement, to complete amputation and even death from sepsis.
An adult female manatee presented with a severe unilateral monofilament line entanglement in October 1999. The flipper had abnormally grown around and incorporated the line into its matrix with a purulent exudate. Systemic antibiotics (amikacin 5 mg/kg IM and procaine penicillin G 15,000 IU/kg IM) were administered. At the time of rescue, she was in a mating herd with seven male manatees. Working under the assumption that mating had been successful, she was treated as a pregnant animal. Serum progesterone levels were followed. It is unclear what levels, or for what duration, of progesterone confirm pregnancy in the manatee. However, opportunistic clinical samples from rehabilitating animals provide more data. Pregnancy was confirmed with ultrasound imagery.
The initial surgery was done under midazolam (0.045 mg/kg IM) and meperidine (0.5 mg/kg IM) sedation and local anesthesia using a lidocaine ring block around the flipper. Three points were followed into the fibrous tract using hemostats to secure the line. As much line as could be grasped was removed. A small amount of surgical debridement was done. The animal was reversed with flumazenil equal volume to midazolam (5 mg/ml). Remaining line and purulent exudate were evident 1 week following the initial surgery. A second surgery was done approximately 1 month later, to allow recovery of blood loss. The same sedation and local anesthetics were used. The midazolam was repeated at a 0.022 mg/kg dose 2 hours into the surgical procedure. The second surgery involved an aggressive debulking and debridement of the affected bone. More line was removed. The wound was packed using Hemaseel™ Fibrin Glue(G) with amikacin 250 mg/ml to provide local delivery of antibiotics. Many wound dressings were used during the entire recovery period. One week following the second surgery, purulent exudate and more monofilament line was evident. A viable fetus was confirmed using ultrasound imagery prior to a third surgery. The decision to amputate was based on a persistent osteomyelitis that endangered the manatee’s life, and field observations of manatees leading normal lives in the wild with only one flipper. Midazolam was used at the same levels as the prior surgery. However, meperidine was dropped to a 0.25 mg/kg dose to minimize any effects on the fetus. Bupivacaine 0.75% was used for the flipper ring block. To minimize blood loss, a harmonic scalpel and electrocautery were used for the amputation. A major concern was the large plexus of arteries and veins that runs medially to the humerus. The open wound was thoroughly irrigated, and cyanoacrylate spray was used as a temporary water-resistant cover. One month following the amputation ultrasonography showed an active viable fetus.
A current moratorium that does not allow breeding of manatees in captivity precludes gestational data to be collected in captivity. Opportunistic clinical samples from rehabilitating manatees offer important data in the interim. Groups and agencies are working on programs to collect and educate the public on the threat that discarded fishing line and other debris has on this endangered species.
The authors wish to thank Ethicon (harmonic scalpel usage), Haemacure Corporation (Fibrin glue), Sonosite Inc. (Ultrasound machine usage), The University of Miami Department of Neurosurgery, The Miami VA Hospital, and Avian and Exotic Animal Medical Center for their valuable contributions to this case.
1. Nishiwaki M. General biology. In: Ridgway SH, ed. Mammals of the Sea Biology and Medicine. Springfield, Illinois: Bannerstone House; 1972:193.
2. Walsh MT, Bossart GD. Manatee medicine. In: Fowler ME, ed. Zoo & Wild Animal Medicine Current Therapy 4. Philadelphia, PA: W.B. Saunders Co.; 1999:516.