FISHERY BULLETIN: VOL. 70, NO. 1 



DEPTH OF OPENING 



In the first few trials (Fioure 5-1) a marked 

 difference existed in the response of Westward 

 to an opening: 1.1 m deep and one 0.61 m deep. 

 The animal swam slowly at the surface, circling 

 or moving back and forth in the chamber. When 

 the opening was 1.1 m deep, she moved slowly 

 through the opening .iust as the moving wall 

 closed. When the opening was 0.61 m deep, she 

 moved past or circled slowly in front of the open- 

 ing and then dove and entangled herself in the 

 webbing of the moving wall. In the sixth trial, 

 her behavior became more varied; she swam in 

 tight circles beneath the surface and attempted 

 to pass between the end of the moving wall and 

 the periphery of the chamber before passing 

 through the opening, after which she slapped 

 her tail against the water surface. Behavior in 

 subsequent trials became increasingly erratic. 

 In trial 13 she darted through the opening rather 

 than moving through slowly as in the previous 

 trials. In trial 14, she tried again to squeeze past 

 the moving wall and became lodged in the narrow 

 opening. In trial 15, she assumed a position 

 across the corkline of the moving wall, half in 

 and half out of the chamber, and remained there 

 until removed. In the remaining trials, she 

 moved rapidly through the opening, and in the 

 last two, she assumed a horizontal attitude sim- 

 ilar to that usually taken by the trained ])or- 

 poi.se and .stop])ed bobbing her head but still kept 

 her blowhole above the surface. 



An identical experiment (II) of alternating 

 trials was carried out 5 days later, after all traces 

 of the slow surface-swimming and head-bobbing 

 l)ehavior had disappeared. Performance was 

 consistently higher with the 1.1-m opening. The 

 effect of depth is clearly seen in the results of a 

 block-design experiment for Westward (III). 



The second naive porpoise, Moana, a smaller 

 and presumably younger animal than Westward, 

 achieved a higher rate of successful passage in 

 the first depth experiment (Figure 6-1). She 

 failed only once, with the 1.1-m-deep opening. 

 In the .second depth experiment (II) her per- 

 foi-mance was extremely variable compared to 

 that of Westward, and no relation between depth 

 and success rate existed. In two trials (18 and 



20) while swimming in tight circles near the 

 apex of the chamber, she snagged her flipper in 

 the webbing and had to be extricated. In later 

 block-design experiments (V and IV) the effect 

 of depth was evident as it was for Westward. 



WIDTH OF OPENING 



Results of block-design experiments testing 

 the effect of width of opening for Westward 

 (Figure 5-V) and for Moana (III) were similar 

 to those for the trained porpoise (Nohea), but 

 an effect was discernible at widths of 1.5 m. 



As with the other experiments, performance 

 of Westward was higher and more stable than 

 that of Moana. Westward began to pass through 

 the opening two or three times during a single 

 trial. The frequency of multiple "escapes" was 

 higher for the 5.5-m-wide opening than for the 

 narrower openings (Table 4). 



CORKLINE 



Insertion of a corkline at the surface across 

 the top of the opening sharply affected the per- 

 formance of Westward (IV) and Moana (V). 

 The performance of Moana showed the greatest 

 effect. After a series of preparatory trials, 

 Moana failed to pass through the opening in five 

 straight trials with the corkline. In each trial 

 she laid the anterior part of her body across the 

 corkline and remained there until removed. In 

 the block-design experiments with Westward 

 (IV), the second block of trials with a corkline 

 produced a smaller drop in performance than did 

 the first, with the 0.61-m-deep opening only, dem- 

 onstrating as for the trained porpoise (Nohea 

 IV, Figure 4) an interaction between depth and 

 presence or absence of a barrier at the surface. 



Table 4. — Multiple escapes of Westward. 



56 



