Grusha and Patterson: Quantification of the drag and lift of pop-up satellite archival tags 



65 



Wildlife Computers 



ditions. The weight of the tag is 

 only important during accelera- 

 tions and decelerations. During 

 acceleration, the mass of the tag 

 positively affects the magnitude 

 of two separate forces that add to 

 the hydrodynamic drag, and like- 

 wise during deceleration, these 

 extra forces develop on the at- 

 tachment point that could cause 

 tag loss. 



The motivation for this study 

 is to determine the feasibil- 

 ity of tagging cownose rays {R. 

 bonasus) with PSATs to study 

 their fall migration. By quanti- 

 fying the forces that act upon an 

 animal when a PSAT is attached, 

 and using published metabolic 

 rates, we can estimate the en- 

 ergetic cost for the ray to carry 

 a PSAT. Moreover, this type of 

 analysis can be used to determine 

 the minimum size of ray suitable 

 for tagging. Considering the wide 

 variety of user-determined modifications that 

 can be implemented in applying these tags, 

 this experiment is intentionally designed to 

 isolate the PSAT from other variables. In 

 this way, these results can be applied to a 

 broad range of applications so that each user 

 can decide the manner in which a specific 

 modification of the tag is likely to affect the 

 forces of lift and drag. 



Methods 



Drag was measured on two brands of PSAT. 

 One tag was manufactured by Wildlife Com- 

 puters, Inc. (Model PAT, 16150 NE 85 th St 

 #226, Redmond, WA 98052) and the other was 

 a mock tag made by Microwave Telemetry, Inc. 

 (Model PTT-100, 10280 Old Columbia Road, 

 Suite 260, Columbia, MD 21046) weighted to 

 simulate a functional tag. The two tags are 

 very similar in size and shape (Fig. 1). The 

 Wildlife Computer PAT has a body length of 

 180 mm (not including the antenna) and a 

 dry weight of 75 g and the Microwave Telem- 

 etry PTT is 175 mm long and weighs 68 g. 

 Measurements were obtained in a 22,700- 

 liter freshwater recirculating flume 24 meters in length 

 located at the Virginia Institute of Marine Science. A 

 30-g spring scale was used to measure force and was 

 suspended above the flume. A 1.25-cm low-friction Delrin 

 rod was suspended approximately 55 cm below the water 

 surface by a metal bracket and placed directly below the 

 spring scale. A 90-cm length of 0.46-mm diameter (20-lb 

 test) monofilament line connected the tag to the spring 



Length- 180 mm 

 Weight- 75 g 



Length -175 mm 

 Weight - 68 g 



Figure 1 



The shape and dimensions of two brands of pop-up satellite archival tag. 



Diagra 

 tion of 



Figure 2 



m of experimental design, showing how 0, the angle of deflec- 

 the tag, was measured. 



scale by loops tied at either end. One loop was threaded 

 through the release pin in order to lasso the tag. The 

 other loop was then attached to the clip on the spring 

 scale and the tag was passed under the Delrin rod so that 

 it floated to the other side (Fig. 2). The depth of the Delrin 

 rod and the length of the monofilament were selected 

 so that the tag was completely immersed in the water 

 throughout the experiment and so that it floated within 



