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



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 1 - 

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0.15 



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 0) 



0.15 



m 



1 5 10 15 20 25 30 35 40+ 



Current=10-19 cm/sec 

 n = 1009 median=19 



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15 10 15 20 25 30 35 40+ 



Current = 20-29 cm/sec 



n = 1499 median=16 



10 15 20 25 30 35 40+ 



005 - 



Scombnds and carangids 



Current=30-39 cm/sec 

 n=206 median =12 



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1 5 10 15 20 25 30 35 40+ 



15 10 15 20 25 30 35 40+ 



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Current = >49 cm/sec 

 n=92 median = 5 



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10 15 20 25 30 35 40+ 



Length (mm) 



Figure 3 



Size distributions of fishes collected by light traps from all platforms at different current speed intervals. 

 The total number offish collected [n) and the median length (mm) over each interval are included. Size 

 distributions are further subdivided by three general ecological groupings: clupeiforms (Clupeidae and 

 Engraulidae), demersal taxa (i.e., more substrate-oriented fishes such as synodontids and blenniids), and 

 scombrids and carangids. 



significantly different from each other (P=0.11). The 

 decrease in the frequency of fishes larger than 10 mm 

 at the higher current intervals was not limited to any 

 particular ecological grouping, i.e., pelagic fishes such 

 as clupeiforms, scombrids, and carangids were as rare 

 as demersal taxa. 



Turbidity 



Mean total CPUEs generally decreased with increasing 

 turbidity (Fig. 4). Highest catches (CPUEs >50 fish per 

 10 min) predominantly occurred at turbidities below 

 1.0 NTU, whereas at higher turbidities catches were 

 generally lower. There was a significant linear relation- 

 ship between log-transformed mean total CPUE data 

 and mean turbidity (log 10 (y+l) = -0.25.v + 1.48, r 2 =0.08; 

 F=11.86, P=0.0007). 



The majority of the dominant families showed a simi- 

 lar pattern of highest mean CPUEs at turbidities <1.0 



NTU, and relatively low mean CPUEs at higher turbidi- 

 ties (Fig. 5). Clupeidae, however, showed a pattern of 

 high CPUEs at turbidities <0.5 NTU and between 1.0 

 and 2.0 NTU. 



Discussion 



Light trap catches of larval and juvenile fishes appeared 

 to be negatively affected by increasing current speeds at 

 platforms. This was expected because stronger currents 

 may interfere with a fish's ability to swim to and enter 

 a light trap (Doherty, 1987; Thorrold, 1992; Anderson 

 et al., 2002). Doherty (1987) predicted that, for station- 

 ary (anchored or tethered) light traps, catches should 

 increase initially with current speed as more water 

 is sampled, but then decrease as current speed inter- 

 feres with catchability. Although mean total CPUEs 

 clearly decreased with increasing current speed, they 



