Validation of otolith-based ageing 

 and a comparison of otolith and 

 scale-based ageing in mark- 

 recaptured Chesapeake Bay 

 striped bass, Morone saxatilis 



David H. Secor 

 T. Mark Trice 



Chesapeake Biological Laboratory 



Center for Estuarine and Environmental Sciences 



The University of Maryland System 



RO. Box 38. Solomons, Maryland 20688-0038 



Harry T. Hornick 



Maryland Department of Natural Resources, Fisheries Division 



C2 Tawes State Office Building 



580 Taylor Avenue, Annapolis, Maryland 21401 



Anadromous striped bass, Morone 

 saxatilis, populations in the mid- 

 Atlantic region comprise important 

 commercial and recreational fish- 

 eries (ASMFC 1 ). Stock assessments 

 for these fisheries depend upon age 

 estimates using annular structures 

 of scales (Merriman, 1941; Man- 

 sueti, 1961; Kahnle et al. 2 ; Hornick 

 et al. 3 ). Age estimation for large 

 adults (>91 cm) has been problem- 

 atic owing to the presence of false 

 annuli and to difficulty in interpret- 

 ing narrow annuli in peripheral 

 fields of the scale (Scofield, 1928a; 

 Merriman, 1941; Tiller, 1950; 

 Mansueti, 1961). Recent work on 

 otolith microchemistry to decipher 

 environmental histories of migra- 

 tory striped bass has provided age 

 estimates that were considerably 

 greater than those previously re- 

 ported (Secor, 1992). Longevity of 

 female Chesapeake striped bass 

 was estimated to exceed 31 years 

 based on examination of otolith mi- 

 crostructure (Secor et al. 4 ). 



An investigation of the rate of 

 annulus formation in the otoliths 

 of Chesapeake Bay striped bass 



was performed to verify estimates 

 of growth and longevity (Secor et 

 al. 4 ). For otolith microchemistry 

 applications (Secor, 1992), it also 

 was critical to verify that annuli 

 formed at a yearly rate so that sea- 

 sonal patterns in Sr/Ca ratio (ex- 

 posure to varying salinity) could be 

 interpreted. Heidinger and Clod- 

 felter (1987) reported yearly rates 

 of annulus formation in otoliths of 

 striped bass from one to four years 

 in age in a midwest reservoir, but 

 no specific measurements of accu- 

 racy or precision were presented. 

 No other studies have been pub- 

 lished on annulus formation in 

 striped bass otoliths. 



A mark-recapture study on 

 hatchery-produced striped bass 

 (Rago et al., 1993; Hornick et al. 3 ) 

 provided samples of known-age 

 resident and migratory fish that 

 were 3 to 7 years old. From 1985 to 

 1992, approximately 5.5 million 

 juvenile striped bass were stocked 

 in Chesapeake Bay tributaries 

 (Rago et al., 1993). All fish were 

 implanted with a binary-coded wire 

 tag which indicated year of origin 



and provided information on their 

 hatchery source and release date 

 and site. The objective of this study 

 was to verify the rate of annulus 

 formation by comparing annulus 

 counts with the known age of re- 

 captured hatchery fish. A second 

 objective was to compare scale and 

 otolith ages of large striped bass 

 (>91 cm, total length [TL]) to de- 

 termine the accuracy of age esti- 

 mates derived from scales. 



Methods 



Known-age study 



Striped bass otolith ageing tech- 

 niques were verified by using two 

 sets of known-age, coded-wire 

 tagged (CWT) adults. Agroup of 24 

 CWT fish was obtained from a col- 

 laborative study of migratory 

 striped bass conducted by the 

 Maryland Department of Natural 

 Resources (DNR); the National 

 Marine Fisheries Service; the 

 North Carolina Department of En- 



1 ASMFC (Atlantic States Marine Fisher- 

 ies Commission). 1990. Source document 

 for the supplement to the striped bass 

 FMP-Amendment No. 4. Atlantic States 

 Marine Fisheries Commission. Prepared 

 by Versar, Inc., Columbia, MD, 414 p. 



2 Kahnle, A. W., D. Stang, K. Hattala, and 

 W. Mason. 1988. Haul seine study of 

 American shad and striped bass spawn- 

 ing stocks in the Hudson River estuary. 

 New York State Dep. of Environmental 

 Conservation, Albany, NY. 



3 Hornick, H. T., R. K. Schaefer, D. T. 

 Cosden, K. J. Booth, J. L. Markham, C. B. 

 McCollough, D. M. Goshorn, M. L. Gary, 

 W. S. Barbour, and R. J. Dickinson. 1992. 

 Investigations of striped bass in Chesa- 

 peake Bay. USFWS Federal Aid Perfor- 

 mance Report. Project F-42-R-5. Maryland 

 Dep. Natural Resources, Tidewater Ad- 

 ministration, Fisheries Div., 219 p. 



4 Secor, D. H., H. T. Hornick, and J. Mark- 

 ham. Lost and found generations of Chesa- 

 peake Bay striped bass: improvement in 

 year-class representation of Chesapeake 

 Bay striped bass due to the 1985-1991 

 Maryland striped bass moratorium. 

 Unpubl. manuscr. 



Manuscript accepted 23 May 1994. 

 Fishery Bulletin 93:186-190 ( 1995). 



186 



