NOTE Lindquist and Shaw: Effects of current speed and turbidity on catches of larval and juvenile fishes 



443 



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Mean water turbidity(NTU) 



Figure 5 



Mean CPUE per sampling set (from within- and off-platform light traps) in relation to the mean turbidity 

 per sampling set for each of the dominant families collected. Data from all platforms were combined. Note 

 changes in the scale of the y-axis. Not shown in the Engraulidae plot were three points from 551 to 606 

 CPUE between 0.2 and 0.5 NTU. 



particles may have been flushed from the platforms and 

 their associated biofouling communities by currents. 

 In a comparison of light trap catches between adjacent 

 beach and rocky shore habitats, Hickford and Schiel 

 (1999) attributed lower catches at the beach to lower 

 water clarity caused by sediment resuspension by wave 

 action. Therefore, high current speeds at platforms may 

 have indirectly affected light trap catch efficiency by 

 reducing water clarity. 



Results from this study have clear implications for 

 future studies with light traps. At platforms, light trap 

 CPUEs began to decline noticeably at current speeds 

 of 30 cm/sec, and by 40 cm/sec catches of active swim- 

 ming larval stages (i.e., all but preflexion stages) were 

 rare. This finding suggests that, for comparison studies. 



estimates of relative abundance from light traps may be 

 biased where there is considerable variation in current 

 flow (Doherty, 1987; Anderson et al., 2002). Drifting 

 traps may be used to avoid the confounding effect of 

 differential water flow (Thorrold, 1992); however such 

 a deployment method may not be applicable when habi- 

 tats of interest are fixed (e.g., platforms, coral reefs). 

 In such cases, the best course may be to not consider 

 light trap samples at high current speeds (240 cm/sec). 

 For turbidity, study results were not as clear; however, 

 temporal or spatial variation in turbidity also would 

 undoubtedly bias light trap results. Short of using light 

 traps at times or locations of similar water clarity, an 

 adjustable light source may be incorporated into light 

 trap design so that equivalent light intensities, and 



