FISHERY BULLETIN: VOL. 70, NO. 1 



as the "naive porpoise," were freshly captured, 

 were not exposed to any training: procedures 

 prior to the experiments, and were tested imme- 

 diately upon arrival at the Institute. 



THE APPARATUS 



The crowdinjr chamber (Fig-ure 1) was con- 

 structed in a large pool at the Oceanic Institute. 

 The pool, known as "Bateson's Bay," is roughly 

 circular, 24.7 m across at its greatest diameter, 

 and approximately 1 m deep at its center. A 

 smaller holding tank communicates with the 

 jwol through a wooden gate. Three hemisjiher- 

 ical underwater viewing ports allow surveillance 

 of the entire pool. 



Net barriers were placed at various points 

 along the pool wall to construct a circular en- 

 closure or crowding chamber about 20 m in di- 

 ameter in which j^orpoise were tested. The 

 crowding chamber had two radial walls of net- 

 ting that extended from the outer edge of the 

 chamber to a central aluminum mast. One of 

 the walls was stationary and was provided with 

 escape openings of various dimensions. The 

 other wall was movable and was used to drive 

 the animals through the opening in the sta- 



tionary wall. The movable wall pivoted on the 

 central mast and was supported along the leading 

 edge by an aluminum beam and on the distal end 

 by a plastic float. The edge of the pool was 

 marked at 1° intervals. 



The walls were made of tuna purse-seine web- 

 bing (4Vi.-iiich stretched mesh [10.8 cm] *42 

 thread knotted nylon). Flotation was provided 

 by purse-seine-type corkline constructed of 

 6-inch diameter x 3V^-inch (15 >( 9 cm) sponge- 

 plastic floats. 



The basic escape opening was 18 ft (5.5 m) 

 wide and 6 ft (1.8 m) deep. Flaps of purse- 

 seine webbing were laced in, to variously de- 

 crease width to 10, 5, or 2V2 ft (approximately 

 3.0, 1.5, or 0.8 m) and/or depth to 31/2, 3, 2, 1, or 

 1/2 ft (approximately 1.1, 0.9, 0.6, or 0.2 m) . For 

 tests of response to a barrier across the opening 

 at the water surface, a corkline constructed of 

 hollow plastic floats (5 y 9 inch [13 X 23 cm], 

 4 per m) was strung across the top of the open- 

 ing. In tests of response to barriers of acous- 

 tically low-reflective materials, a panel of 3%- 

 inch (stretched) mesh (8.6 cm) *12 monofila- 

 ment webbing, a panel of 0.38-mm-thick poly- 

 vinyl sheeting, or a panel of 1.04-mm-thick poly- 

 vinyl sheeting, was laced into the opening. 



STATIONARY 

 CONTAINING 

 NET WALL P 



STATIONARY 

 CONTAINING 

 NET WALL 



Figure 1. — Crowding chamber. 



Largest diameter of pool is 80 feet, 

 to scale. 



Sketch not drawn 



50 



