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Fishery Bulletin 103(1) 



the central portion of the flume. Prior to the experiment, 

 the monofilament line was attached to the spring scale 

 and the spring scale was then set at zero so that the 

 weight of the monofilament line was excluded from the 

 subsequent measurements. The flume temperature was 

 measured at 20°C. Measurements were taken on each 

 tag at flume velocities of 0.0, 0.15, 0.30, 0.45, and 0.60 

 m/s, the maximum velocity of the flume. At each flume 

 velocity, the flume flow was allowed to equilibrate for 10 

 minutes. Then spring scale measurements were observed 

 over a period of five minutes and the mid-point measure- 

 ment and its range were recorded. The raw measurement 

 was then converted to total force, F T (N): 



F T = (rawmeasurement(g))(lkg/1000g)(9.8m/s 2 ). (3) 



In addition, a digital photo was taken of each tag 

 at each velocity from the side of the flume in order to 

 measure the angle of deflection (6) as measured upward 

 from horizontal. Accordingly, the total force {F T ) could 

 then be separated into its component forces, lift (F L ) 

 and drag (F D ): 



F L = sin 6 F T , 



F D = cos F T . 



(4) 

 (5) 



Results 



The spring scale measurement for the Wildlife Comput- 

 ers PAT increased from 6.50 g at 0.00 m/s to 19.0 g at 

 0.60 m/s and the Microwave Telemetry PTT increased 

 from 11.75 g to 21.5 g over the same flume velocity 

 increase (Table 1). Because of increasing turbulence 



in the flume at the two higher flume velocities, the 

 range of the spring scale measurements also increased. 

 The total force exerted by the Wildlife Computers PAT 

 increased from 0.064 N to 0.186 N as the flume velocity 

 was increased (Table 1). Similarly, the drag and calcu- 

 lated power required to pull the tag through the water 

 column at the highest velocity was 0.159 N and 0.095 W, 

 respectively. The lift of this PSAT also increased, but not 

 continuously, from 0.064 N to 0.097 N. The forces exerted 

 by the Microwave Telemetry PTT were very similar but 

 had higher lift values. The total force increased from 

 0.115 N to 0.211 N, the drag increased to 0.159 N and 

 the power required to pull this PSAT was 0.095 W at the 

 highest velocity. The lift increased from 0.115 N to 0.140 

 N but again not in a continuous manner. Force-velocity 

 curves for both PSATs were very similar (Fig. 3). Lift 

 was relatively constant for each tag, although at differ- 

 ent magnitudes. Total force and drag both increased over 

 the range of flume velocities and roughly paralleled each 

 other between 0.30 m/s and 0.60 m/s. 



Discussion 



Considered alone, the power required to pull a given 

 PSAT at a particular velocity has little relevance, but 

 when considered in the context of an animal's usual 

 energy expenditure to swim at that velocity, it can be 

 expressed as %TAX (Tag Altered eXertion), defined as 

 the increase in energy required by the animal to pull the 

 PSAT at the specified velocity, normalized by the routine 

 or active metabolic rate (see below). In his biotelemetry 

 studies, Blaylock (1992) measured mean routine swim- 

 ming speeds between 0.20 m/s and 0.29 m/s in cownose 

 rays. Maximum swimming speeds for cownose rays have 



