Discovery rate is assumed to be approximately equal in all methods cited 

 here since exposure of all prey groups to the predators is complete and equal. 

 This parameter is best measured by recording the reactive distance to the prey 

 item (Beukema, 5), a difficult task which is not addressed in any of the above 

 techniques. 



Attack rate can influence differential predation rate in that certain 

 characteristics of the prey may be perceived by the predator and produce 

 active selection. This behavior could occur in predation tests u'here 

 simultaneous introduction of treated and control prey groups occur, as in the 

 methods employed by Bams (2), Coutant (8), and Kania and O'Hara (16). 

 However, as Bams noted, this parameter cannot be quantified by these 

 methods because group identity of individual prey is not discernible during 

 attacks. 



Differences in capture rate between prey groups are a result of differences in 

 prey ability to evade an attacking predator. The techniques used by Bams (2), 

 Coutant (8), and Kania and O'Hara (16) cannot discern between differences in 

 capture rate and differences in attack rate since the overall result of predation 

 is measured, and not individual attacks and captures. It is in this regard tliat the 

 method devised by Yocum and Edsall (27) is superior, because it specifically 

 measures the actual instantaneous predation rate as affected by changes in the 

 rate of capture. Although Sylvester (25) also measured rate of capture (in 

 terms of mean survival time), Yocum and Edsall found excessive variance 

 between predator groups in time-to-capture when using his method. Of the 

 various techniques, those of Yocum and Edsall (27), Bams (2) and Coutant (8) 

 are considered best suited for laboratory predator-prey studies. The technique 

 used by Kania and O'Hara (16), is similar to that of Coutant and Bams, but 

 with the addition of an escape area. This modification Hmits its application to 

 those prey species with a specialized behavioral characteristic of shallow water 

 refuge. Also, there is a probable compUcation of learning, as prey become 

 familiar with the predator's area, and the "safe", shallow, screened area used in 

 the tests. Finally, the 60 hour test duration is fairly lengthy. 



In this particular study with larval fish prey. Bams' (and Coutant's) method 

 of simultaneous presentation of prey from different treatment groups could 

 not be utilized, as a tag to distinguish prey treatment groups is necessary. 

 Common methods for identification, such as fin clipping and cauterization 

 branding, were not feasible with larval prey. A visual dye is unacceptable 

 because of potential alteration to predator-prey relationships due to 

 conspicuousness of prey and color preferences in the predator. A number of 

 fluorescent dyes were tested, but successful dyes were found to alter normal 

 behavior in fish larvae (Pseudopleuronectes americamis). Efforts to label fish 

 larvae with a radioisotope were also unsuccessful. Due to these difficulties 



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