29 



Age Classification 



Age classifications were determined from a sample of torrent sculpins electroshocked in 

 Libby Creek (T30N R31W sect. 36 SW) on October 18, 1991. Five distinct age classes 

 were evident from the length-frequency histogram of 119 torrent sculpins (Figure 13). Age 

 (young of the year) appear infrequently in the data due to sampling bias. Many age 

 were visible in the backwater areas but slipped through the large mesh of the nets but the 

 general size of the age class appeared to be around 3.0 cm. Age I sculpins ranged from 

 3.7 cm to 5.2 cm. Age II sculpins ranged in size from 7.0 cm to 8.1 cm. Age III sculpins 

 ranged in size from 8.2 cm to 9.4 cm. Age IV sculpins ranged in size from 9.8 cm to 10.8 

 cm. Age I sculpins made up the largest percentage of the sample although the age class 

 was not effectively sampled. The population of each progressive age class decreased in the 

 sample. The age IV class contained 6 individuals the largest of which was 10.8 cm. 



Length-weight regressions were carried out on age I through age IV class torrent 

 sculpins in Libby Creek. The sample contained a wide range of weights due to the low 

 sensitivity of the scale being used. As a result, length-weight regressions are projected in 

 Appendix B but not included in the results and discussion. 



Sampling Methodology 



The electroshocker, in combination with the D-net, yielded the highest catch per unit 

 effort of all the sampling methods employed during this study. The D-net was placed 

 directly downstream of the electroshocker. Sculpins immobilized or attempting to escape 

 the electrical field often drifted or swam into the D-net. Occasionally checking the D-net 

 yielded a sculpin via the "blind grab". Despite the fact that sculpins were typically capable 

 of eluding the electrical field, this technique proved to be the most effective means of 

 sampling sculpins. 



