DEVELOPMENT AND DISTRIBUTION OF LARVAE 



AND JUVENILES OF SEBASTOLOBUS 



(PISCES; FAMILY SCORPAENIDAE) 



H. Geoffrey Moser' 



ABSTRACT 



The North Pacific scorpaenid genus Sebastolobus is composed of three deepwater coastal species of 

 potential commercial importance. They are oviparous and produce bilobed gelatinous egg sacs that 

 float to the surface waters where hatching and larval development occur. Transformation into pelagic 

 juveniles occurs at about 20 mm length. The pelagic stage of S. alascanus is relatively short-lived, as 

 they transform into benthic juveniles at 22 to 27 mm length. In the deep-living S. altivelis the 

 juveniles remain pelagic for well over a year and grow as large as 56 mm. 



Larvae of the two species mentioned are collected regularly on plankton surveys of the California 

 Cooperative Oceanic Fisheries Investigations (CalCOFI) and pelagic and benthic juveniles are com- 

 mon constituents of mid-water and bottom trawls taken in the CalCOFI region. In this paper speci- 

 mens from these sources are used to describe the larval and juvenile stages of the two species and to 

 show the striking morphological changes which occur during development. Also presented are data 

 on geographic distribution and patterns of seasonal abundance of larvae. Larvae of Sebastolobus 

 smaller than 10.0 mm could not be distinguished to species. 



Knowledge of the life history of the scorpionfish 

 genus Sebastolobus is scanty. Pearcy (1962) de- 

 scribed the floating egg masses, the developing 

 embryos, and the newly hatched larvae of Sebas- 

 tolobus. The larvae of Sebastolobus occur in the 

 plankton collections of the California Coopera- 

 tive Oceanic Fisheries Investigations (CalCOFI) 

 and can be differentiated from those of Sebastes 

 on the basis of the spination of the parietal ridge 

 (Ahlstrom, 1961). Information on the distribution 

 and abundance of Sebastolobus larvae in Cal- 

 COFI has hitherto not appeared in the literature, 

 nor has a description of the larval stages. It is the 

 purpose of this paper to fill that void and also to 

 describe the distinctive juvenile stages of S. al- 

 tivelis and S. alascanus, which are common con- 

 stituents of mid-water trawl catches in the east- 

 ern North Pacific. 



The three known species of Sebastolobus 

 inhabit the coastal waters of the North Pacific. 

 Sebastolobus altivelis ranges from the southern 

 tip of Baja California to the Aleutian Islands 

 while S. alascanus is found from northern Baja 

 California to the Bering Sea and the Commander 

 Islands off the Asiatic mainland. The Asian 

 species, S. macrochir, ranges from the coast of 

 Japan northward to the Bering Sea south of Cape 



'Southwest Fisheries Center, National Marine Fisheries 

 Service, NOAA, La Jolla, CA 92037. 



Navarin and into the Sea of Okhotsk (Barsukov, 

 1964). At present the commercial catch of Sebas- 

 tolobus is small, however, data of Best (1964) and 

 Alverson, Pruter, and Ronholt (1964) suggest 

 that these fishes may constitute a substantial re- 

 source in the deep coastal waters of the northeast 

 Pacific. 



The taxonomic characters of the adult mem- 

 bers of this genus have been reviewed by a 

 number of investigators (Starks, 1898; Hubbs, 

 1926; Matsubara, 1943; Phillips, 1957; Barsukov, 

 1964; Miller and Lea, 1972). Sebastolobus is dis- 

 tinguished from other scorpaenid genera by the 

 unusual pectoral fins, each of which is separated 

 by a notch into dorsal and ventral lobes, by pos- 

 sessing more vertebrae (28 to 31) and dorsal 

 spines (15 to 17), a complete set of circumorbital 

 bones, an uppermost pectoral radial which is free 

 from the scapula, and by a suborbital stay with a 

 broad posterior end anchored firmly onto the 

 preopercular bone. The two North American 

 species may be separated on the basis of the 

 shape and number of rays in the spinous dorsal 

 fin. In S. altivelis the third spine is the longest 

 while in S. alascanus the fourth or fifth spine is 

 the longest. The former species usually has 15 

 (rarely 16) spinous dorsal rays while the latter 

 has 16 or 17 (rarely 15) rays. Also, S. altivelis 

 usually has 29 (rarely 28) vertebrae and S. alas- 

 canus has 30 (rarely 31). The Asian species, S. 



Manuscript accepted January 1974. 

 FISHERY BULLETIN; VOL. 72. NO. 4. 1974. 



865 



