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Fishery Bulletin 91(1). 1993 



search for food once the effects of handling subsided. 

 Fish in warmer water would be expected to have a 

 higher demand for food at any time in the experiment 

 due to a higher metabolic rate. Further, small fish 

 should have a higher demand than larger fish. In- 

 creased demand for food should be met by an increase 

 in the volume searched per unit time. 



The means by which a fish increases the volume 

 searched per unit time depends on the type of search- 

 ing employed (i.e., sweep vs. saltatory). Search vol- 

 ume for sweep searchers is proportional to the dis- 

 tance traveled. A sweep searcher in warmer water 

 should swim faster, for longer periods, and/or pause 

 less often. For saltatory searchers, search volume is 

 directly proportional to pause frequency. Saltatory 

 searchers can scan greater volumes by increasing 

 both pause frequency and swimming speed between 

 pauses. In the absence of suitable prey, their pause 

 duration should be constant and only as long as nec- 

 essary to scan each field completely. Our results for 

 total activity and mean bout duration from the sta- 

 bilized levels of control experiments follow the pre- 



dictions for a sweep searcher: In warmer water, ac- 

 tivity is higher, pause frequency is shorter, and the 

 duration of active bouts is longer. Predictions for a 

 saltatory searcher are contradicted, since pause fre- 

 quency is not higher in warmer water. In fact, the 

 opposite is true for small fish, which should be most 

 strongly affected by hunger. 



Conclusion 



Experimental conditions cannot mimic the various 

 natural scenarios of transient temperature fluctuation. 

 Diel temperature changes are usually gradual and pre- 

 dictable. Yet, even when acclimated to regular circa- 

 dian cycles, swimming behavior may be influenced by 

 ambient temperature (Fuiman 1986). Traversing a ther- 

 mocline is more abrupt, but it is predictable and at 

 least partly voluntary, allowing for some degree of 

 physiological preparation. Such vertical migrations 

 can be beneficial to a fish's daily energy budget (Brett 

 1971, Wurtsbaugh & Neverman 1988), but there may 



