PERRIN and HUNTER: ESCAPE BEHAVIOR OF PORPOISE 



Acoustical tests carried out by the Naval Under- 

 sea Research and Development Center, San Di- 

 ego, Calif., on plastic sheeting of similar thick- 

 nesses indicated effective acoustic transparency 

 in the range of porpoise emanations (personal 

 communication from W. E. Evans). 



PROCEDURES 



The moving wall was rotated around the cen- 

 ter mast at a rate sufficient to completely close 

 the chamber in about 4 min. An attempt was 

 made to maintain a constant rate of rotation. 

 Time required for an animal to escape from the 

 chamber was recorded in seconds with a stop- 

 watch, and position of the moving wall at time 

 of escape was recorded in degrees. The reading 

 in degrees was later used to calculate surface 

 area remaining in the crowding chamber at time 

 of escape. The wall was rotated alternately 

 in clockwise and counterclockwise directions. 

 After escape of an animal, the moving net wall 

 was rotated until it was against the stationary 

 wall, and the two radial nets remained together 

 until the beginning of the next trial. Trails were 

 spaced initially at 15-min intervals, to allow time 

 for changing the escape opening. After our pro- 

 ficiency in altering the opening increased, the in- 

 terval was decreased to 10 min. 



Two major types of experimental design were 



used : ( 1 ) a long series of trials alternating two 

 treatments and (2) a series of blocks of consec- 

 utive trials of various treatments. In some ex- 

 periments, the two approaches were combined 

 to yield a factorial design testing simultaneously 

 the effects of variation in two or three of the 

 factors of width, depth, and presence or absence 

 of corkline, monofilament, or polyvinyl barriers. 

 In some tests of the monofilament and polyvinyl 

 panels, the animal was subjected to a single trial 

 with the panel after a series of learning trials 

 without the jianel or at the beginning or conclu- 

 sion of an experiment involving other variables. 

 The design of these experiments is referred to 

 below as "single trial." The results of the first 

 series of experiments (Waimea I, II, and III; 

 see Table 2) using the alternating trials design 

 indicated a probable influence by the direction 

 of rotation of the net wall or by stage of practice 

 effect. The small number of trials in each ex- 

 ]-»eriment precluded complete randomization, but 

 the treatments in subsequent experiments were 

 staggered to offset the effect of direction of ro- 

 tation. A typical sequence of trials was: a, h, 

 a, b, a, a, h, a, b, b; where a and b were different 

 treatments, and rotation in the first trial was 

 clockwise, in the second counterclockwise, and 

 so on in alternating fashion. In this manner, an 

 equal number of clockwise and counterclockwise 

 trials was assured for each treatment. 



Table 2. — Preliminary experiments with trained porpoise. 



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