MASON and MACHIDORI: POPULATIONS OF SYMPATRIC SCULPINS 



Age Determination 



Following dissection, otoliths were dried for 

 several days and then immersed in a 50% solu- 

 tion of glycerin and water. Otolith structure was 

 not clear when examination immediately fol- 

 lowed removal of the otolith from the specimen. 

 Otoliths of specimens preserved for more than 1 

 mo were partly decomposed by the preservative. 



Whole otoliths were examined under a dissect- 

 ing microscope by reflected light against a black 

 background. In both species, the otolith had an 

 opaque nucleus around which were arranged con- 

 centric, alternating hyaline and opaque bands 

 extending to the margin. The opaque band 

 reflected rapid summer growth and the hyaline 

 band constituted the annulus. The first hyaline 

 band around the nucleus was not considered an 

 annulus but is assumed to reflect initial post- 

 larval growth, perhaps prior to the onset of a 

 benthic existence. The newly forming annulus 

 was readily discernible in specimens collected in 

 October and December. 



Length-frequency histograms were found use- 

 ful to identify the young of the year (age 0) and 

 yearlings (age I). 



RESULTS 



General Life History 



Both species of sculpins in these short coastal 

 streams are "coastal" forms (McAllister and 

 Lindsey 1960) which spawn during April and 

 May. The prickly sculpin undergoes a down- 

 stream spawning migration in the early spring 

 (Mason 1974a) and spawns in the estuary as re- 

 ported previously by Krejsa (1967). The coast- 

 range sculpin has been reported to make down- 

 stream migrations coincident with C. asper 

 (Shapovalov and Taft 1954; Hunter 1959) but no 

 such migration was recorded in Lymn Creek 

 where C. aleuticus spawned in situ throughout its 

 range in the stream as found in Alaskan streams 

 by McLarney (1968). 



The breeding males are territorial and court 

 one or more females which deposit clusters of 

 adhesive eggs on the underside of large rocks or 

 debris forming the nest site. Following spawning, 

 the females depart and the males guard the eggs 

 until hatching. The newly hatched and trans- 

 parent larvae begin swimming upon hatching 

 and assume a pelagic life for some 30 days, grow- 



ing from 5 mm at hatching to 12 mm in length 

 before assuming a benthic existence. 



In the laboratory at 10°-12°C, the eggs of both 

 species were eyed at 9-10 days; the larvae were 

 active at 15 days; and hatching occurred 19-20 

 days following fertilization. Hatching commenced 

 in Lymn Creek on or before 11 May when water 

 temperature reached 10° C. On this date, larvae 

 began appearing in the driftnet catches and were 

 taken for some 5 wk until 19 June. 



From drift net catches of the larvae in Lymn 

 Creek, coupled with laboratory studies on the 

 reproduction of both species, we concluded that 

 the eggs and larvae are euryhaline but survival 

 and growth of cultured larvae are better in sea- 

 water. Feeding on microplankton commenced 

 some 6-10 days following hatching of cultured 

 larvae when the yolk was noticeably depleted and 

 when most stream larvae were either in the 

 estuary or, in the case of coastrange sculpin 

 larvae, in the lower stream near the estuary. 

 Since the average size of the latter larvae in drift 

 samples from four stations located along 1,150 m 

 of stream above the estuary equalled that of 

 6-day-old larvae in culture at similar tempera- 

 tures, these larvae probably spend several days in 

 the nest vicinity and in downstream transport 

 following hatching. 



Within several hours of hatching, larvae of 

 both species swam to the water surface and main- 

 tained themselves vertically immediately be- 

 neath the surface film by steady swimming 

 movements. This behavior was sustained through 

 the 25 days of culture in both fresh water and 

 seawater. Tests on 5-day-old and older larvae 

 showed that they were positively rheotactic at 

 velocities greater than 1 cm/s and swam actively 

 against the current in short bouts of rapid 

 swimming. 



Post-spawned C asper remained in the estuary 

 of Lymn Creek throughout the summer and early 

 fall. Their return to upstream areas may coincide 

 with the spawning runs of salmon that commence 

 in October (Mason 1974a). The offspring of both 

 species remain in the estuarine zone until the 

 early summer of the following year when they 

 proceed to invade upstream areas. 



Distribution and Relative Abundance 



Both sculpin populations were limited to the 

 lower reaches and estuaries of all four streams, 

 with coastrange sculpins distributed farthest up- 



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