Use of carfentanil and a ketamine-xylazine mixture to immobilise wild grey seals (Halichoerus grypus)

Carfentanil was used to anaesthetise 46 adult grey seals (Halichoerus grypus) on 78 occasions during two breeding seasons. The mean dose was 9.92 micrograms/kg bodyweight during the first season and 10.22 micrograms/kg during the second. Naloxone hydrochloride was used as the antagonist, averaging 0.53 mg/kg and 1.73 mg/kg over the two periods although the latter is probably unnecessarily high. Ketamine and xylazine at a ratio of 5:1 were also used during the same two seasons, 57 seals being anaesthetised on 104 occasions. The average dose of ketamine was 4.96 mg/kg and 5.15 mg/kg with xylazine in proportion. Complications arose on a number of occasions and these are discussed.