Table 42, --Pregnancy rates determined from Japanese and United States 

 age determinations of fur seal teeth, by age. United States pelagic 

 collection, 1964 



DRUG IMMOBILIZATION OF FUR SEALS 



A drug that would effectively immobilize 

 adult male fur seals would be useful in 

 furthering certain kinds of research on these 

 animals. Immobilization with drugs admin- 

 istered by projectile syringe eliminates the 

 need for physical restraint that might injure 

 the animals or be hazardous for the investiga- 

 tor to apply. Numerous drugs, giving a wide 

 variety of responses, have been used success- 

 fully on several species of animals, Harthoorn 

 (1965) reviews much of the research on this 

 subject. The choice of drugs depends mainly 

 on the specific effect desired, but also on 

 species -related drug idiosyncracy (a given 

 drug may produce the desired effect in one 

 species but not in another). 



Territorial males that are to be marked 

 for studies of behavior should be immobilized 

 with a drug which will wear off quickly so 

 that the animals can effectively resume de- 

 fense of themselves and their territories. 

 Peterson (1965) found a succinylcholine su- 

 perior to several other drugs and combina- 

 tions of drugs in this respect but could not 

 determine a safe and effective dosage. Estab- 

 lishment of the proper dosage of any drug, 

 however, depends on a fairly uniform rate of 

 absorption of a drug of uniform strength. 

 Peterson contended with considerable varia- 

 tion in both. The strength of solutions of 

 succinylcholine varies because the drug de- 

 composes very rapidly after it is in solution, 

 and rate of absorption varies because as- 

 similation of the drug is slower in fatty 

 tissue than in muscle. Peterson's target for 

 injecting succinylcholine was the lattisimus 



dorsi, a muscle which lies between two layers 

 of blubber. There was no way to prevent 

 deposition of the drug short of or beyond 

 this muscle into fat. 



Keyes (1966) minimized variations in 

 strength and absorption by injecting solutions 

 of freshly reconstituted crystalline succinyl- 

 choline into the relatively fat-free muscular 

 hump of the neck. In general, the rate of 

 absorption is proportional to the concentra- 

 tion of a drug, and rapid effect is followed 

 by rapid recovery; hence, recovery time can 

 be reduced by increasing the concentration 

 of a drug in solution. Keyes induced rapid 

 recovery by injecting concentrated succinyl- 

 choline with 1- and 2-cc. syringes rather 

 than those of 10-cc, capacity used by Peter- 

 son. 



Keyes used these techniques on nine adult 

 male seals (table 43). In the first three 

 animals, the latent period (time from injection 

 to first signs of effect) was 5 to 8 minutes; 

 complete imnnobilization lasted 1 1 to 20 nnin- 

 utes, and the time from injection to full re- 

 covery was 24 to 34 minutes. Thus, the 

 critical time lapses were considerably less 

 than the average latent period of 12 minutes 

 and recovery period of 48 to 95 minutes ob- 

 served by Peterson, and the period of im- 

 mobilization was longer (11 to 20 minutes 

 comipared to 3 to 10 minutes). Male number 

 9 Wis somewhat larger than the first three 

 but died after being given the same dosage; 

 however, he was handled and marked whereas 

 the others were not. Since wild animals 

 paralyzed by succinylcholine are fully con- 

 scious, they experience great anxiety when 

 approached and particularly when handled. 

 This emotional stimulation intensifies and 

 prolongs the action of succinylcholine by in- 

 creasing the animal's production of acetyl- 

 choline, a molecule with an effect similar to 

 that of succinylcholine. Death from suffoca- 

 tion results from prolonged and more com- 

 plete paralysis of the thoracic muscles. Death 

 might also be caused by heart failure because 

 of a sharp rise in blood pressure caused by 

 stimulation of the sympathetic nervous sys- 

 tem (Harthoorn, 1965). Perhaps if the animals 

 were first given a sedative, paralysis would 

 be less intensive and of shorter duration. 



Because 50 mg. of succinylcholine had 

 little or no effect and 60 mg. was at times 

 lethal, we conclude that when used alone 

 succinylcholine has a margin of safety too 

 narrow for routine use on territorial male 

 fur seals. 



Anectine, Burroughs Wellcome. Trade names referred 

 to In this publication do not imply endorsement of com- 

 mercial products. 



42 



