22 



Alvin L. Braswell and Ray E. Ashton, Jr. 



Table 3. Comparative Necturus lewisi capture success on different substrates. 

 Number of sampling efforts for each substrate category given in paren- 

 theses. Percentages are success rates for each category. 



Substrates 



Capture 

 success 



Bedrock 



(14) 

 (1) 



6.7% 



(15) 



Loose 

 rocks 



Sand/ 

 gravel 



(293) 

 (65) 



18.2% 



(358) 



Clay/ 

 hard soil 



(26) 

 (20) 



43.5% 



(46) 



Muck & 

 detritus 



Negative 

 Positive 



Totals 



(39) 



(11) 



22.0% 



(50) 



(214) 



(60) 



21.9% 



(274) 



The potential effects of changes in water level on capture success 

 were tested by recording no change, general rise, or .general fall in water 

 level during a trapping period. Table 4 shows relative capture success 

 for each of the three catergories. Capture success rates were signifi- 

 cantly higher when the water levels rose than when they remained con- 

 stant. Capture success rates during drops in water levels did not differ 

 significantly from those obtained when levels were rising or when they 

 were constant. 



Table 5 shows the relationships between capture success rates and 

 different levels of precipitation observed during a sampling period. No 

 significant differences were found. 



Capture success compared to water turbidity is shown in Table 6. A 

 significantly higher success rate was observed in the 0-20 (Secchi disc) 

 category over all other categories except the 81-98 category. The differ- 

 ence between the 0-20 and 81-98 categories, though not significant, does 

 not disrupt the pattern of greater capture success in the most turbid 

 waters. 



For examination of digestive tract contents 153 N. lewisi were 

 divided into two groups: 36 larvae (20-50 mm SVL) and 1 17 adults (91 + 

 mm SVL). Too few specimens were available in the 51 to 90 mm SVL 

 size range to allow comparisons. Since adults were trapped, they could 

 have been in a trap for 0-3 days prior to collection, and their capture of 



Table 4. Comparative Necturus lewisi capture success during changing water 

 levels. Number of sampling efforts for each water level change in par- 

 entheses; percentages are success rates for each condition. 

 Capture Water levels 



success 



No change 



(41) 



(5) 



10.9% 



Rise 



Fall 



Negative 

 Positive 



(173) 

 (56) 



24.5% 



(229) 



(305) 



(60) 



16.4% 



Totals 



(46) 



(365) 



