Necturus lewisi Study: Distribution & Ecology 29 



Little Fishing creeks in Warren and Halifax counties, and Swift Creek 

 in Nash County. 



Comparing trap capture success to factors such as water levels, 

 stream temperatures, precipitation, turbidity, time of day, and season 

 provides some information on activity patterns. Activity away from 

 cover and consequent capture in traps usually occurs at night and when 

 stream temperature ranges between 0° C. and 18° C. Temperature 

 changes within this range seem to have little effect on activity. 



Although precipitation seems to have no direct effect on activity, 

 the rising water levels and high turbidity it produces show a positive 

 correlation with increased activity. The "cover" that turbidity provides, 

 and increase in terrestrial food items produced by runoff and rising 

 water, may trigger greater activity under these conditions. 



The difficulty encountered in trapping N. lewisi during warm and 

 hot seasons is currently inexplicable, but other authors have suggested it 

 may relate to activity patterns of predatory fish. Neill (1963) and Shoop 

 and Gunning (1967) alluded to this possibility to explain the activity 

 patterns observed in N. beyeri and N. maculosus louisianensis, which 

 are similar to those seen in N. lewisi. Fish migrations and spawning 

 activity markedly increase in April when minimum stream temperatures 

 routinely exceed 18 degrees C. Thus, this temperature may represent a 

 threshold above which N. lewisi cannot forage abroad without serious 

 threat from predators. There are, however, alternative hypotheses. For 

 one thing, warming water correlates with egg deposition and subsequent 

 nest guarding by N. lewisi (Ashton and Braswell 1979). In addition, 

 April and May are months in which potential prey such as crayfish, 

 other invertebrates, and fish increase in number due to recruitment of 

 young into their populations. A greater supply of food could greatly 

 reduce foraging activities. Shoop and Gunning (1967) indicated that 

 crayfish of the genus Procambarus were the primary food of N. macu- 

 losus and N. beyeri in Louisiana. (See Cooper and Ashton, this publica- 

 tion, for information on crayfish associates of N. lewisi in the study 

 areas.) 



Analysis of digestive tract contents of adult N. lewisi shows that a 

 wide variety of aquatic invertebrates, aquatic vertebrates, and terrestrial 

 invertebrates are acceptable food items. The diet of larvae is largely 

 restricted to aquatic invertebrates, mostly arthropods. The size of the 

 prey item that a certain size class of salamander can accomodate seems 

 to be the most important factor in prey selection. 



Prey consumed by adults indicates that they visit a broad range of 

 habitats on feeding forays. Prey items that are routinely found in flow- 

 ing and slack waters, in leaf beds, under logs and rocks, and in sand and 

 gravel, were present in their digestive tracts. 



