Pearson et al.: Age, growth, and potential yield of Sebastes jordani 



405 



and growth completion rate (Pauley 1980). We used 

 mean annual temperature for Ascension Canyon at a 

 depth of 200 meters (8°C, Lynn et al. 1982). We did 

 not estimate M using a catch curve (Ricker 1975) 

 because shortbelly rockfish size tends to increase with 

 depth and latitude (Lenarz 1980). For that reason, our 

 opportunistic samples would not be expected to pro- 

 duce an unbiased estimate of the true age distribution. 



Results and discussion 



Age and growth 



The edge-type analysis of broken and burnt otoliths 

 supported our interpretation that marks were formed 

 annually, generally between December and April 

 (Fig. 1). This was similar to the findings of Kimura 

 et al. (1979) for yellowtail rockfish S.flavidus and one 

 month earlier than for widow rockfish 5. entomelas 

 (Lenarz 1987). 



Between- and within-reader agreement was higher 

 for shortbelly rockfish than for other rockfish species. 

 Between-reader agreement was 76% to the year and 

 87% within one year; within-reader agreement was 

 77% to the year and 95% within one year (Fig. 2). 

 Using whole otoliths, Six and Horton (1977) reported 

 between-reader agreement for yellowtail rockfish 

 S. Jlavidus to be 24% to the year and 71% within one 

 year. For canary rockfish S. pinniger, Six and Horton 

 (1977) reported within-reader agreements of 37 and 

 21% to the year for whole and sectioned otoliths, 

 respectively. The higher levels of agreement for short- 

 belly rockfish could be due in part to their relatively 

 young age, as percent agreement declined with increas- 

 ing age beyond about age 4 (Fig. 2). 



The comparison between ages derived from examina- 

 tion of the otolith surface and from broken and burnt 

 halves revealed a systematic bias for fish older than 

 age 4. Ages obtained from the otolith surface tended 

 to be less than ages obtained from broken and burnt 

 otoliths (Fig. 3). Beamish (1979) and Stanley (1986) 

 reported similar results for Pacific ocean perch 

 S. alutus. 



Shortbelly rockfish live substantially longer than 

 previously reported. The oldest fish we found was 22 

 years old as opposed to the previous estimate of 12 

 years (Lenarz 1980). There have been similarly large 

 revisions in estimated maximum age of commercially 

 important groundfish species off the west coast of 

 Canada (Beamish and McFarlane 1987). Only 2 of 23 

 species were estimated to have maximum ages less 

 than 20 years, and 13 Sebastes spp. (not including 

 S. jordani) had maximum ages ranging from 36 to 

 140 years (Beamish and McFarlane 1987). 



Fitted growth curves differed significantly by sex, 

 with males having a slower growth rate and a smaller 

 maximum size (F crit (3, 1000, 0.01) = 3.80, F calc = 

 115.23) (Fig. 4). Although sample sizes were small, 

 there was some evidence that the oldest females were 

 smaller than somewhat younger females (Fig. 4). This 

 could be due to shrinkage in older fish through senes- 

 cence (Liu and Walford 1969); natural selection favor- 

 ing small, older fish that use available energy for 

 reproduction rather than continued growth (Leaman 

 and Beamish 1984); or higher mortality for faster- 



