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Fishery Bulletin 104(4) 



with a general lack of confidence in surface age esti- 

 mates. This uncertainty, coupled with the observation 

 that otoliths of larger, presumably older, fish tend to 

 grow in thickness rather than in sagittal diameter, led 

 to pilot work for processing and production (large-scale) 

 aging of Greenland halibut sagittae. Various methods 

 reported in the literature and several new techniques 

 were explored. This pilot work converged on a method 

 that involved cutting the left sagitta in the transverse 

 plane and staining the two restulting cross sections. 

 This method is similar to the break-and-burn method 

 (Chilton and Beamish, 1982) but is more amenable 

 to fragile Greenland halibut sagittae. The goal of the 

 present study was to determine whether the precision of 

 Greenland halibut age estimates could be improved by 

 examining the stained cross sections of their sagittae 

 rather than the surfaces of the whole sagittae, and to 

 determine whether there was a significant difference in 

 age estimates made with each of the two methods. 



Materials and methods 



Otoliths were collected from Greenland halibut in July 

 1998 and June-August 1994 as part of the AFSC Bering 

 Sea and Aleutian Islands trawl surveys. Sagittae were 

 removed at sea and stored in a glycerol-thymol solution 

 until the time of our study. Fish length (TL) was mea- 

 sured to the nearest centimeter for each specimen. 



Surface aging was accomplished by submerging sag- 

 ittae in water over a black background and counting 

 probable annuli (i.e., translucent zones) with a dissect- 

 ing microscope (6-25x) with reflected light. Probable 



annuli were counted along several vectors on both sides 

 of the right and left sagittae. A count that was repeat- 

 able, with highest reader confidence, was adopted as the 

 surface age estimate. 



The left sagitta (i.e., on blind side offish) was embed- 

 ded in clear polyester resin and cut into two pieces with 

 a low-speed saw. The cut was made slightly obliquely 

 to the transverse plane and was adjusted for each oto- 

 lith to ensure that the saw blade bisected the nucleus, 

 passed through a thick section of the perisulcular re- 

 gion (i.e., a portion with a large mediolateral dimen- 

 sion), and extended out the center of a prominent dorsal 

 finger (Fig. 1). The two exposed cross sections were then 

 polished with 800-grit wet-dry sandpaper on a lapidary 

 wheel to remove saw marks. 



Staining techniques were adapted from Richter and 

 McDermott (1990). Polyester blocks containing cut oto- 

 liths were submerged in a solution of 1% Aniline Blue 

 WS (no. B362-03. Mallinckrodt Baker Inc., Phillipsburg, 

 NJ) in 17f acetic acid. Staining times varied from 10 to 

 15 minutes initially and were consolidated to 13 min- 

 utes as the experiment progressed. Stain solution tem- 

 perature was maintained between 20° and 23°C. Upon 

 removal from the stain, otoliths were rinsed with fresh 

 water and wiped clean to ensure that residual acid 

 and stain were removed. The two cross sections were 

 covered with mineral oil to eliminate glare, and were 

 examined under a dissecting microscope at 12x to 50x 

 magnification with reflected light. Blue stained translu- 

 cent zones (Fig. 2) were counted, and this number was 

 adopted as the cross-section age estimate. 



Three trials were conducted to examine the possible 

 benefits of cutting and staining Greenland halibut sagit- 



