The potential use of otolith 

 characters in identifying larval 

 rockfish [Sebastes spp.) 



Thomas E. Laidig 

 Stephen Ralston 



Southwest Fisheries Science Center 



National Marine Fisheries Service. NOAA 



3 1 50 Paradise Drive. Tiburon, California 94920 



Rockfish of the genus Sebastes are 

 commercially important in the 

 northeast Pacific Ocean, where 

 more than 60 valid species are rec- 

 ognized (Eschmeyer et al., 1983). 

 Although morphological and chro- 

 matic characters are used routinely 

 to identify adults of the genus, such 

 traits are frequently ineffective for 

 young of the year, especially larvae. 

 Like most fish, early developmen- 

 tal stages of Sebastes spp. have less 

 pigmentation, fewer hard struc- 

 tures (e.g. fin rays), and show less 

 differentiation when compared 

 with adults. However, an ability to 

 discriminate among the larvae of 

 the many rockfish species is criti- 

 cal to the advancement of early life 

 history studies in this group. 



A variety of methods have been 

 used to identify larval and juvenile 

 rockfish (Kendall, 1991). Although 

 pigmentation is the most fre- 

 quently used character (Moser et 

 al., 1977; Laroche and Richardson, 

 1980; Moser et al., 1985; Kendall 

 and Lenarz, 1987), size at extrusion 

 (Moser et al., 1977), meristic counts 

 (Moser et al., 1977), morphometries 

 (Morris, 1956), size at specific life 

 history events (Stahl-Johnson, 1985), 

 time of parturition in conjunction 

 with geographic location (Moser et 

 al., 1977), and electrophoretic pat- 

 terns (Seeb and Kendall, 1991) 

 have all been used to identify lar- 

 val and juvenile rockfish. 



A problem with many of these 

 techniques, however, is that larval 

 characters often undergo ontoge- 

 netic change. To overcome this 

 problem, the larvae of many species 

 have been reared in captivity and 

 sequentially sacrificed. This is not 

 only technically demanding, expen- 

 sive, and time consuming, but dif- 

 ferences in development between 

 laboratory and wild fish may affect 

 the number, size, and distribution 

 of the attributes under investiga- 

 tion. Thus, permanent identifiable 

 characters would be useful. A static 

 trait, which retained its character- 

 istics throughout early life, would 

 increase our ability to positively 

 identify rockfish larvae. Otoliths, 

 being acellular aragonitic concre- 

 tions, are good candidates to retain 

 features produced during the lar- 

 val stage. Likewise, otoliths have 

 been shown to contain sufficient 

 variation among species (Hecht and 

 Appelbaum, 1982; Akkiran, 1985; 

 Victor, 1987) and stocks (Messieh, 

 1972; Postuma, 1974; McKern et al, 

 1974; Neilson et al., 1985; Smith, 

 1992) to assign with accuracy group 

 membership to individuals. 



This study investigates the po- 

 tential of using otolith microstruc- 

 ture to assist in the identification 

 of larval rockfish. We assume that 

 no change occurs to early larval 

 otolith microstructure once it is 

 deposited (Brothers, 1984; Steven- 



son and Campana, 1992). Otolith 

 characteristics (nuclear shading 

 patterns, nuclear radius, and first 

 increment width) produced during 

 the early larval period were de- 

 scribed and measured from late lar- 

 val and pelagic juvenile stage speci- 

 mens of eight species of rockfish: 

 Sebastes auriculatus, S. entomelas, 

 S. flavidus, S. goodei, S. jordani, 

 S. mystinus, S. paucispinis, and S. 

 saxicola. These species were the 

 most numerous rockfish species 

 collected off the central California 

 coast during the study period. 



Methods 



Field collections 



Samples of young-of-the-year pe- 

 lagic juveniles and late larvae were 

 collected with a midwater trawl ( 12 

 x 12 m) from the National Oceanic 

 and Atmospheric Administration 

 RV David Starr Jordan. From 1983 

 to 1989 nine cruises were conducted 

 off central California (lat. 36°30- 

 38°10'N) during the months of 

 April-June. Pelagic juvenile rock- 

 fish were frozen at sea and re- 

 turned to the laboratory for final 

 identification. Wyllie Echeverria et 

 al. (1990) have described cruise 

 sampling methodology in detail. 



Laboratory procedures 



Pelagic juveniles were identified to 

 species from external characteris- 

 tics, including pigmentation, fin- 

 ray counts, and gill-raker counts 

 (Laidig and Adams, 1991). The sag- 

 ittal otoliths were removed and af- 

 fixed whole to microscope slides 

 and were prepared for viewing with 

 the methods outlined in Laidig et 

 al. (1991). 



Otoliths were examined with a 

 video image interfaced with a digi- 

 tizer (Laidig et al., 1991). Distinct 

 reoccurring shading patterns in the 



Manuscript accepted 15 June 1994. 

 Fishery Bulletin 93:166-171 (1995). 



166 



