MASON and MACfflDORI: POPULATIONS OF SYMPATRIC SCULPINS 



AGE-CLASS 



Figure 8. — Annual growth rates (weight) of Coitus aleuticus 

 and C. asper in Lymn, Chef, and Waterloo creeks. 



population, which was first sampled in early 

 April, was most rapid during the spring and early 

 summer and nearly completed by mid-August. 

 The largest coastrange sculpin captured was 145 

 mm in length and 8 yr old while the largest prickly 

 sculpin was 144 mm in length and 6 yr old. 



Length-weight linear regressions based on 

 logged data were calculated for both species in 

 the three largest streams (Table 6) and compared 

 by analysis of variance. The length-weight rela- 

 tion was similar for both species in all three 

 streams except for the coastrange sculpin in 

 Chef Creek, which was considerably lighter per 

 unit length than in the other two systems (F2 2737 

 = 77.5). Slow annual growth and a lower slope 

 (6) may reflect poorer feeding conditions or as- 

 sociated population stress during the late sum- 

 mer when the flow in a 500- to 600-m section of 

 this stream becomes intermittent. 



Estimates of average annual mortality for both 

 species of sculpins in Lymn, Cabin, and Chef 

 creeks ranged between 58 and 75%, the differ- 

 ences between species and streams depicted in 

 Figure 9 being statistically non-significant. Al- 

 though similar for both sculpins, mortality in 

 Waterloo Creek was considerably lower than in 

 the other three streams 38-40%. No estimate of 



Table 6. — Length-weight regression parameters (log y = 

 a + bx) for Cottus aleuticus and C. asper in three streams 

 on Vancouver Island, B.C. 



annual mortality was attempted for C asper in 

 Chef Creek due to the small population present. 

 Despite close agreement to the linear function 

 of the majority of point estimates, some points for 

 young and old age-classes deviated considerably 

 and are taken to indicate poor survival, low re- 

 cruitment of subyearlings from the estuary in 

 some years, or inadequate sampling. For exam- 

 ple, poor survival of age I of C. asper is indicated 

 for Lymn, Waterloo, and Cabin creeks (Figure 9). 

 Similarly, age of both species were poorly repre- 

 sented in Waterloo Creek, as were age in Chef 

 Creek, despite intensive sampling in the down- 

 stream areas in which they were distributed. In 

 Chef Creek, age IV of C. aleuticus was very poorly 

 represented, suggesting either a sudden exten- 

 sive mortality or inadequate sampling effort in 

 the larger pools upstream where these fish reside. 



DISCUSSION 



The ecological importance of cottid fishes in the 

 simple fish communities of these coastal streams 

 remains essentially unknown but the present 

 findings appear to be timely in view of the resurg- 

 ing interest in enhancing the natural production 

 of anadromous stream salmonids. Previous 



10.000 



1000 



I 



to 



O 



q: 100 



m 



s 



< 

 jr 10 



y Vr yl 

 AGE-CLASS 



TV 



Figure 9. — Declining numbers with increasing age within 

 sympatric populations of Cottus aleuticus and C. asper in 

 four streams. Straight lines describe least-square regressions 

 of best fit. 



139 



