Abstract

Understanding foraging behavior and body condition of adult female Steller sea lions (Eumetopias jubatus) is a critical data need, but also the most difficult to obtain due to the high risk of capture mortality. A previous study in Steller sea lions using a combination of zolazepam-tiletamine resulted in unacceptably high mortality rates and several of the animals in that study died as a result of drowning in open water and in small pools on the haul-out soon after darting. During November 2010 we immobilized six adult female Steller sea lions observed with pups in Southeast Alaska using a combination of medetomidine-butorphanol-midazolam (dosage range approximately 0.038–0.044, 0.13–0.15, and 0.19–0.22 mg/kg respectively) via remotely delivered dart at distances of approximately 12–20 meters. This combination and dosages were derived from those used in a preliminary study in adult male California sea lions (Zalophus californianus). Steller sea lions were darted using a Daninject^TM Model JM Special CO₂ rifle and 3.0 ml Daninject^TM dart syringes.

Three animals (206–238 kg) were approached approximately 12 minutes after darting and were found on the haul-out at a deep plane of anesthesia; allowing for intubation, branding, satellite-telemeter attachment and collection of morphometrics, blood, blubber and whisker samples to assess health status and diet. Animals were supplemented with isoflurane (range 0.5–1.5%) in 100% oxygen to maintain anesthesia for ≤ 130 minutes. Heart rate, respiratory rate, body temperature, oxygen saturation and blood gases were monitored throughout the procedure. Physiological parameters were within expected ranges except blood glucose, which was elevated and increased over time. Animals were reversed with naltrexone (30 mg) and atipamezole (45 mg) via intramuscular injection. Animals were mobile and alert 9–12 minutes after injection of reversal agents, and post-handling foraging behaviors were monitored using Mk10 Argos Fast-GPS transmitters (Wildlife Computers Ltd.). All three animals continue to be tracked > 90 days post-capture.

Three additional darted animals entered the water after injection and were followed to verify survival. One of these animals was followed to an adjacent haul-out and monitored for 85 minutes at which time she was seen progressively more alert and entering and exiting the water. Two other animals that entered the water after darting were found deeply sedated but spontaneously breathing on their own while floating in the water. The first of these was followed for up to 145 minutes after darting. This animal was deeply sedated but alert enough to avoid capture. The animal became progressively more alert and was seen diving normally and resurfacing to avoid the observation boat. The second of these animals was darted with the reversal agent in the water at approximately 63 minutes after delivery of the immobilization agents. The animal was seen actively diving to avoid pursuit and was seen hauling out shortly after. This preliminary study resulted in successful reversible immobilization of adult animals on haul-outs. Equally important we demonstrated that animals entering the water after darting survived with the use of this combination.