Woodbury: Reduction of growth in otoliths of Sebastes entome/as and S. flavidus 



681 



observed to be narrower than adjacent annuli. 

 To quantify this observation, measurements of 

 annuh were made on these otoliths, as well as 

 additional otoliths obtained from an ongoing 

 port sampling program. Otoliths were collected 

 from male and female widow and yellowtail 

 rockfish landed at Eureka, California, and fe- 

 male widow rockfish landed at Bodega Bay, 

 California, during 1989 and 1990. 



The annulus was defined as otolith growth 

 from the end of one summer to the end of the 

 following summer (approximately October 

 through September). Using reflected light on 

 the distal surface of whole otoliths, I observed 

 that summer growth appears as a white ring 

 and winter growth as a dark ring (Fig. 1). An- 

 nuli from 366 otoliths were measured by using 

 one of the two following methods. With the first 

 method, a camera lucida was mounted atop a 

 dissecting microscope, which was used to trace 

 the surface annuli from 115 female yellowtail 

 rockfish otoliths collected at Cordell Bank. A 

 digitizing pad was used to measure the area of 

 each annulus from the tracings. One or two 

 otoliths per hour could be processed with this 

 method. The remaining 251 otoliths were ana- 

 lyzed by using an image enhancement system 

 comprising a personal computer interfaced with 

 a dissecting microscope and a high resolution 

 closed-circuit video camera. A mouse-driven 

 crosshair was used to trace the annuli displayed 

 on the monitor This method increased produc- 

 tion by sixfold. The area of each annulus (mm-) 

 was square-root-transformed prior to analysis. 

 To compare the two methods, annuli from five 

 otoliths measured by the first method were 

 remeasured by using the second method. The 

 differences in the estimated growth from these 

 five otoliths ranged from 0.2 to 11.4%, with a 

 mean of 2.9%, which represented a minor error 

 compared with observed interannual growth 

 differences. 



Potential problems arise when measuring all 

 the annuli in an otolith. When these rockfish 

 species reach sexual maturity and somatic 

 growth slows, the reduced growth rate is re- 

 flected in their otoliths. Therefore, it would be 

 impossible to determine if a reduction in otolith 

 growth was caused by poor environmental con- 

 ditions or from energy being diverted into go- 

 nadal development. In addition, annuli formed after 

 the onset of maturity are deposited disproportion- 

 ately on the proximal surface of the otolith. It is easier 

 to measure annuli deposited during the immature 

 phase on the distal side of the otolith. To minimize 



Figure 1 



Otoliths from female yellowtail rockfish collected at Cordell Bank. 

 California, showing narrow 1983 annulus (arrow I: (A) 1982, (B) 

 1981, and (C) 1980 year classes. 



these concerns, measurements were restricted to the 

 five annuli formed prior to sexual maturity. Both 

 male and female widow rockfish have an age of 50% 

 maturity of five years, whereas male and female yel- 

 lowtail rockfish are mature at six and seven years. 



