MASON and MACHIDORI: POPULATIONS OF SYMPATRIC SCULPINS 



In upstream areas devoid of C. asper, the large 

 coastrange sculpins were found in habitats which 

 were usually occupied downstream by large 

 prickly sculpins. Although the subyearlings of 

 both species were found in riffle habitats of the 

 intertidal zone, some habitat segregation was 

 evident since prickly sculpins tended to concen- 

 trate in riffle areas where water depth increased 

 and velocity lessened. 



The upstream movement of both sculpins is 

 clearly hindered by minor obstructions in the 

 stream, and their respective upstream distribu- 

 tional limits are marked by similar but different 

 obstructions. These obstructions were usually 

 small log jams involving minor waterfalls al- 

 though in Chef Creek C. aleuticus was stopped by 

 a high waterfall (3-4 m) plunging over bedrock. 

 Obstructions resulting in differences in water 

 level greater than 30 cm were impassable for 

 C. asper while differences greater than 45 cm 

 were necessary to prevent upstream movement of 



Figure 2. — Stream obstructions delimiting the upstream 

 distribution of sculpins in Lymn Creek. A. 45-cm waterfall 

 caused by a large cedar log which blocks the upstream move- 

 ment of Cottus aleuticus. B. 30-cm waterfall at the concrete 

 culvert under Trans-Canada Highway 1, which blocks the 

 upstream movement of C. asper. 



C. aleuticus. The limiting structures in Lymn 

 Creek are shown in Figure 2. 



The upstream limits of both species of sculpin 

 bore a general association with stream gradient, 

 since both stream gradient and frequency of log 

 jams increase with distance upstream, as do 

 streambed disjunctions causing higher falls (Fig- 

 ure 1). 



Both species were distributed downstream into 

 the intertidal zone but to dissimilar extent. For 

 C. aleuticus, the downstream limit was the upper 

 edge of the barnacle zone (station minus 250 m, 

 Figure 1) while C. asper was not collected below 

 the upper edge of the oyster zone (station minus 

 400 m). 



Both sculpins were most abundant in the lower 

 parts of their ranges (Figure 1) although the data 

 for C aleuticus in Chef Creek are inconclusive, 

 possibly due to upstream movement of fish from 

 the region of intermittent flow although such 

 movement was not observed. Skewed distribution 

 is most pronounced in populations of the two 

 smaller streams, Cabin and Lymn creeks, and in 

 large part is due to inequitable distribution of the 

 age-classes. The subyearling sculpins were found 

 to inhabit a narrow zone about the high tide 

 mark, within which the two species showed ex- 

 tensive overlap (Figure 3). The relative contribu- 

 tions of subyearlings to total catches were rather 

 low in Chef and Waterloo creeks, suggesting poor 

 reproductive success or poor recruitment in 1968. 

 This aspect will be dealt with again in a sub- 

 sequent section. 



Neither species of sculpin undertook any obvi- 

 ous seasonal movements in Lymn Creek during 

 the period from August to December (Figure 4), 

 although the large catches of age 1+ prickly 



C. aleuticus 



Casper 



enes of intermittent pools 



during Aug.- Sept in — 



Chet Creek 



«.. LYMN CREEK 

 o- CHEF CREEK 

 i— WATERLOO CHEEK 

 a- CABIN CREEK 



-4,5 -3 3 6 9 



DISTANCE FROM HIGH TIDE MARK (0) IN HUNDREDS OF METERS 



Figure 3. — Autumnal distribution and abundance of sub- 

 yearling sculpins. 



135 



