FISHERY BULLETIN: VOL. 72, NO. 4 



first or second anal fin spines. In the 30- to 40-mm 

 size range the sheath extends posteriad to the 2nd 

 or 3rd anal spine in most specimens and to the soft 

 dorsal fin in some. In most pelagic juveniles of the 

 40- to 50-mm size range the dusky sheath extends 

 back to the soft dorsal and it does so in all speci- 

 mens of the 50- to 60-mm size range. When the 

 juveniles become benthic, the dusky sheath ex- 

 tends posteriad to the caudal fin. 



The fins become deeply and characteristically 

 pigmented in juveniles of S. altivelis. The an- 

 terior portion of the spinous dorsal fin becomes 

 melanistic in specimens as small as 18 mm. In 

 juveniles of the 20- to 25-mm size range the an- 

 terior one-half to two-thirds of the fin is melanis- 

 tic. In the 25- to 30-mm range three-fourths or 

 more of the fin is black. In pelagic juveniles 

 larger than this the pigment has spread onto the 

 soft dorsal fin, and covers both the soft dorsal and 

 soft anal fins in benthic juveniles. 



The bases of the pectoral fins begin to be covered 

 with melanophores in specimens as small as 14 

 mm. In specimens as small as 18 mm the melano- 

 phores extend onto the basal region of the 

 rays. With further growth this black basal zone 

 enlarges posteriad and becomes a highly charac- 

 teristic feature of the pelagic juveniles. The pos- 

 terior mar^n of this zone contrasts sharply with 

 the distal clear region of the fin. In juveniles of the 



19- to 25-mm size range the width of the black 

 basal zone averaged 20% of the fin length. En- 

 largement of this zone is shown by the average 

 relative widths for successive size ranges (25 to 30 

 mm, 38% ; 30 to 35 mm, 46% ; 35 to 40 mm, 54% ; 40 

 to 45 mm, 65%; 45 to 50 mm, 72%; 50 to 55 mm, 

 76%). Towards the end of the pelagic juvenile 

 stage a pale translucent layer covers the basal 

 region of the pectoral fin and thus gives the black 

 zone the appearance of a band. The huge pectoral 

 fins, each with their broad black band, are dis- 

 tinctive features of the pelagic juveniles of S. al- 

 tivelis. When the juveniles become benthic the 

 black zone extends to the tips of the fins. Like the 

 pectoral fins, the pelvic fins also develop a black- 

 pigment zone that enlarges with development. In 



20- to 25-mm juveniles the basal one-quarter to 

 three-quarters of each fin may be black, although 

 in the majority of specimens the basal one-half is 

 black. In the 25- to 30-mm range most specimens 

 have three-fourths or more of the fin black and in 

 juveniles larger than 30 mm either the fin is en- 

 tirely black or the extreme tips of the rays are 

 pigmentless. 



Juvenile pigment begins to appear in S. alas- 

 canus in the 14- to 20-mm size range. The first 

 head pigment to appear is a melanistic blotch on 

 the posterior region of the opercle. This gradually 

 spreads anteriorly onto the cheek and in late- 

 stage pelagic juveniles the entire head is speckled 

 with melanophores. A blotch begins to form over 

 each side of the gut in larvae as small as 15 mm. 

 These enlarge dorsad onto the spinous dorsal fin 

 and posteriad as an irregular mottled sheath that 

 contrasts markedly with the solidly pigmented 

 sheath of S. altivelis juveniles. In the largest 

 pelagic juveniles the mottling on the dorsal fin and 

 trunk extends posteriad to a vertical from the 

 vent. When the juveniles become benthic the 

 mottling spreads onto the remainder of the body 

 and median fins. Melanophores appear on the 

 bases of the pectoral fins in specimens of the 14- to 

 20-mm size range. A faint band of melanophores 

 appears on the rays in some specimens of this size 

 range but never becomes highly developed and 

 covers only the basal one-third of the fin in the 

 largest pelagic juveniles. Likewise a faint band of 

 pigment develops on each pelvic fin in specimens 

 as small as 16 mm and only covers the basal half of 

 the fin in the largest pelagic juveniles. When the 

 juveniles become benthic the pectoral fins develop 

 a pattern of four narrow irregular bands. 



DISTRIBUTION 



The genus Sebastolobus has an exceptionally 

 wide latitudinal distribution in the eastern 

 Pacific. Sebastolobus altivelis ranges from the 

 Aleutian Islands southward to Cape San Lucas, 

 Baja California, andS. alascanus inhabits waters 

 from the Bering Sea to northern Baja California 

 (Barsukov, 1964; Miller and Lea, 1972). The ex- 

 tensive north-south range of Sebastolobus is 

 probably related to habitat depth rather than 

 eurythermy. They are deep-living species 

 throughout their latitudinal range and, as such, 

 experience little change in habitat temperature 

 towards the southern end of their range. Alver- 

 son et al. (1964) reported that significant catches 

 of Sebastolobus are taken at depths shallower 

 than 150 fathoms in the trawl fishery from 

 Oregon to southeastern Alaska, but that the per- 

 centage contribution of Sebastolobus increased 

 with depth. At the maximum depth range sam- 

 pled, 500 to 600 fathoms, Sebastolobus accounted 

 for about 70% of the total fish catch. Southward of 

 Oregon the shoaler elements of the Sebastolobus 

 populations are gradually eliminated and, off 



880 



