342 



Fishery Bulletin 97(2), 1999 



_ 38° 



37» 



76° 



75°30' 



Figure 1 



Lower Chesapeake Bay system, including James, York, and Rappahannock rivers. Points indicate stations where blackcheek 

 tonguefish, Symphurus plagiusa, were collected, April 1994— August 1995. 



diameter (distance from anterior tip of rostrum to 

 postrostrum) was measured to the nearest 0.00001 

 mm by using a compound microscope coupled with a 

 video camera interfaced with a microcomputer 

 equipped with Biosonics' Optical Pattern Recognition 

 System (OPRS) software (Biosonics, Inc., 1987). Be- 

 cause no asymmetry in otolith shape was apparent, 

 sagittal otoliths (left or right) were arbitrarily se- 

 lected from each fish for age analysis, embedded in 

 epoxy resin (Spurr, 1969), and sectioned transversely 

 ( 1 mm thick ) through the core with a Buehler Isomet 

 low-speed saw with duel diamond blades. Sections 

 were mounted on glass slides with Crystal Bond ad- 

 hesive, sanded with 1000-grit sandpaper to remove 

 saw marks and to gain proximity to the core, pol- 

 ished with alumina powder, and examined with a 

 binocular dissecting microscope ( 30x ) with transmit- 

 ted light and bright field. Annuli on otoliths from all 

 566 blackcheek tonguefish were counted once a 



month for three months. Counts were made without 

 information regarding fish length or catch date. In 

 185 (32.7%) cases, the first and second readings did 

 not agree and a third reading was made. The major- 

 ity of disagreements in age estimates occurred dur- 

 ing the beginning of the study; subsequent re-age- 

 ing resolved most discrepancies in age estimates. In 

 most cases, the second reading of an otolith section 

 differed from the first reading by only one year If a 

 third reading agreed with either of the first two, then 

 that age was assigned to the otolith. In 28 (59f ) cases, 

 the third reading was different than the first and 

 second readings. These 28 otoliths were considered 

 unreadable and excluded from further analysis. 



Otolith annuli were validated by the marginal in- 

 crement method (Bagenal and Tesch, 1978; Jearld, 

 1983). Distances from the core to each annulus and 

 the proximal edge were computed by drawing a ver- 

 tical line from the core to the proximal edge of the 



