128 



Fishery Bulletin 102(1) 



?8W 126"W 124°W 122 W 120W 118"W 116°W 



Figure 1 



Map of California and southern Oregon showing the locations ( black dots ) 

 of sablefish sampling and tagging in September and October of 1991. 



determinations, independent age readings seldom are in 

 agreement. This suggests that the methods used to validate 

 the ages were insufficient to allow development of precise 

 aging criteria. The lack of reliable age data has made stock 

 assessments difficult and controversial (Crone et al., 1997 ). 

 and in addition, accurate aging is needed to support eco- 

 logical and habitat studies. 



In September and October of 1991, a tagging and oxytet- 

 racycline (OTC) injection study was included as part of a 

 fish trap survey of the abundance of sablefish in southern 

 Oregon and California. The purpose of this study was to 

 attempt, once more, to improve our ability to reliably age 

 sablefish, thereby improving our ability to manage the 

 species. 



Methods 



trarily selected fish at each station, and the rest of the fish 

 were tagged with blue spaghetti tags. Three of every four 

 tagged fish were injected intraperitoneally with 30 mg of 

 OTC per kilogram offish (Beamish et al., 1983) and the 

 fourth fish was used as a control. A complete description of 

 the survey can be found in Parks and Shaw ( 1994 ). 



A scientist visited the major commercial fishing ports 

 in California and southern Oregon to make port samplers, 

 commercial dealers, and fishermen aware of the impor- 

 tance of the study and to explain handling procedures in 

 the study. A $50.00 reward was offered for the return of 

 whole tagged fish. 



When a tagged fish was returned, the port sampler 

 measured it (fork length in mm), determined the sex, and 

 removed the otoliths. The otoliths were cleaned and stored 

 in painted glass vials (because the OTC mark was light 

 labile) with a 5095 ethanol solution. 



Capture, tagging, injection, and recovery 



In September 1991, the fisheries research vessel Alaska 

 was chartered by the National Marine Fisheries Service 

 to conduct a trap survey from Coos Bay, Oregon, to Cortez 

 Bank, California (Fig. 1). A total of nine sites were visited. 

 At each site seven strings of ten traps were deployed in 

 various depths between 250 and 1900 meters. The traps 

 were retrieved after 24 hours, the catch was removed, and 

 the traps reset for an additional 24 hours. All the sablefish 

 were counted, otoliths were removed from the first 20 arbi- 



Processing of the otoliths 



Two pairs of otoliths were initially selected to develop the 

 procedures to be used in the study. It was found that the 

 OTC mark was very faint and upon heating (as required 

 by conventional age determination methods), the mark 

 disappeared. Accordingly, we developed a method to 

 obtain images of the otoliths before and after heating, and 

 to superimpose the two images of the same otolith; the 

 first viewed under UV light and, the second, after heating, 

 under white light. 



