190 



Timing of hyaline-zone formation as 

 related to sex, location, and year of 

 capture in otoliths of the widow 

 rockfish, Sebastes entomelas 



Donald E. Pearson 



Tiburon Laboratory. Southwest Fisheries Science Center 

 National Marine Fisheries Service. NOAA 

 3150 Paradise Drive. Tiburon, California 94920 



Widow rockfish, Sebastes ento- 

 melas, are an important component 

 of the west coast commercial ground- 

 fish fishery. Annual landings be- 

 tween 1983 and 1992 were 9,700 

 metric tons (Pacific Fishery Man- 

 agement Council 1 ). In addition to 

 widow rockfish, many other rock- 

 fish species are important targets 

 of commercial and sport fisheries. 

 Most stock assessments of rockfish 

 are based on ageing methods (Pa- 

 cific Fishery Management Council 1 ). 

 In most cases, rockfish are aged by 

 the broken-and-burnt otolith method 

 (Chilton and Beamish, 1982). 



Age validation of several rockfish 

 species has been conducted by mar- 

 ginal increment analysis. The fol- 

 lowing species have been validated: 

 yellowtail rockfish, S. flavidus 

 (Kimura et al., 1979); shortbelly 

 rockfish, S.jordani (Pearson et al., 

 1991); chilipepper rockfish, S. 

 goodei (Mellow 2 ); and widow rock- 

 fish ( Lenarz, 1987 ). In all four stud- 

 ies, the hyaline zone formed be- 

 tween December and April. 



Marginal increment analysis re- 

 lies on the assumption that if a hya- 

 line zone is laid down once a year, 

 there should be a clear pattern of 

 periodic growth on the edge during 

 the year. Marginal increment 

 analysis is appropriate only if all 

 fish in the population lay down the 

 hyaline zone at the same time. An 

 annulus would then consist of a 

 single hyaline zone and an opaque 



zone. Conventionally, hyaline zones 

 are counted for age determination 

 purposes. 



The hyaline zone is believed to 

 form during periods of slow growth 

 (Blacker, 1974; Schramm, 1989). 

 Specifically, hyaline-zone formation 

 has been attributed to reproduction 

 (Hostetter and Munroe, 1993), wa- 

 ter temperature (Thomas, 1983; 

 Schramm, 1989), lack of food 

 (Schramm, 1989), and environmen- 

 tal perturbation (Beckman et al., 

 1991). Schramm (1989), in a labo- 

 ratory experiment with bluegill, 

 Lepomis macrochirus, found that 

 low temperature produced a hya- 

 line zone. He was also able to in- 

 duce the formation of hyaline zones 

 by varying photoperiod and re- 

 stricting food intake, but reported 

 that the hyaline zones formed by 

 these environmental agents were 

 much fainter than those resulting 

 from temperature. 



If the hyaline zone is formed ex- 

 clusively by one factor (i.e. repro- 

 duction), and if the factor occurs 

 exactly once a year, at the same 

 time each year, every year, and at 

 the same time in all areas where 

 fish are collected, then samples can 

 be combined from multiple years 

 and different areas. However, Tho- 

 mas ( 1984 ) found that hyaline-zone 

 formation in West African pilchard, 

 Sardinops ocellata, otoliths varied 

 between years, and false marks 

 (checks) were laid down with some 



degree of periodicity. Given the 

 large number of factors known to 

 produce hyaline zones, it seems 

 likely that timing of hyaiine-zone 

 formation is variable. 



Rockfish are ovoviviparous; par- 

 turition occurs about one month 

 after fertilization (Moser, 1967), 

 and thus males expend energy on 

 reproduction at a different time 

 than do females. If spawning is 

 important in the formation of the 

 hyaline zone for rockfish, then it is 

 possible that males do not lay down 

 the hyaline-zone at the same time 

 as females. Failure to account for 

 differences among sexes in the tim- 

 ing of hyaline-zone formation could 

 result in errors in age determination. 



The purpose of this study was to 

 examine the otoliths of an impor- 

 tant rockfish species and to deter- 

 mine whether there were sexual, 

 geographical, or annual variations 

 in the time of hyaline-zone forma- 

 tion. Possible causes of variations 

 in the time of hyaline formation are 

 also discussed. 



Methods 



Sagittal otoliths of widow rockfish 

 were obtained from California and 

 Washington commercial groundfish 

 port sampling programs for the 

 years 1983-87. This interval was 

 selected because in 1983 an El Nino 

 event occurred (Glynn, 1988) and 

 a sequential series of years with 

 adequate sample sizes was desired. 

 Otoliths were collected from widow 

 rockfish caught in northern Califor- 



1 Pacific Fishery Management Council. 



1993. Status of the Pacific Coast ground- 

 fish fishery through 1993 and recom- 

 mended acceptahle biological catches for 



1994. Report of the Pacific Fisheries Man- 

 agement Council, Portland, OR, 467 p. 



- Mellow, J 1993. Bodega Bay Field Of- 

 fice, California Department of Fish and 

 Game, 1785 Highway 1, Bodega Bay. CA 

 94923. Personal commun. 



Manuscript accepted 7 September 1995. 

 Fishery Bulletin 94:190-197 ( 1996). 



