389 
Abstract— An improved radiometric 
aging technique was used to examine 
annulus-derived age estimates from 
otoliths of the Atlantic tarpon, Meg- 
alops atlanticus. Whole otoliths from 
juvenile fish and otolith cores, repre- 
senting the first 2 years of growth, from 
adult fish were used to determine 210 Pb 
and 226 Ra activity; six age groups con- 
sisting of pooled otoliths and nine indi- 
vidual otolith cores were aged. This 
unprecedented use of individual oto- 
lith cores to determine age was possible 
because of improvements made to the 
226 Ra determination technique. The dis- 
equilibria of 210 Pb: 226 Ra for these sam- 
ples were used to determine radiometric 
age. Annulus-derived age estimates did 
not agree closely with radiometric age 
determinations. In most cases, the pre- 
cision (CV<12%) among the otolith 
readings could not explain the differ- 
ences. The greatest radiometric age was 
78.0 yr for a 2045-mm-FL female, where 
the radiometric error encompassed the 
annulus-derived age estimate of 55 
yr by about 4 yr. The greatest radio- 
metric age for males was 41.0 yr for a 
1588-mm-FL tarpon, where the radio- 
metric error encompassed the annulus- 
derived age estimate of 32 yr by 1 yr. 
Radiometric age determinations in this 
study indicated that the interpretation 
of growth zones in Atlantic tarpon oto- 
liths can be difficult, and in some cases 
may be inaccurate. This study provides 
conclusive evidence that the longevity 
of the Atlantic tarpon is greater than 
30 years for males and greater than 50 
years for females. 
Manuscript accepted 26 January 2001 . 
Fish. Bull. 99:389-398 (2001). 
Radiometric age validation of 
Atlantic tarpon. Megalops atlanticus 
Allen H. Andrews 
Erica J. Burton 
Kenneth H. Coale 
Gregor M. Cailliet 
Moss Landing Marine Laboratories 
8272 Moss Landing Road 
Moss Landing, California 95039-9647 
E-mail address (for A H Andrews): andrews@mlml.calstate.edu 
Roy E. Crabtree 
National Marine Fisheries Service 
9721 Executive Center Drive North 
St. Petersburg, Florida 33702-2439 
The Atlantic tarpon ( Megalops atlanti- 
cus) is believed to be a long-lived fish. 
The strongest evidence is from a cap- 
tive female Atlantic tarpon that lived 
to at least 63 years when it died in 
1998 at the John G. Shedd Aquarium in 
Chicago, Illinois. 1 Life in the aquarium, 
however, is difficult to compare with 
life in the natural environment. A simi- 
lar longevity of 55 years was estimated 
from growth zones in sagittal otoliths 
of a wild female tarpon (Crabtree et 
al., 1995). The annual periodicity of the 
growth zones used to estimate age was 
validated by using oxytetracycline up 
to an age of 9 yr in captive fish (Crab- 
tree et al., 1995), but extrapolation of 
these results to older, wild fish, how- 
ever, is fallible. In addition, wild Atlan- 
tic tarpon are highly migratory and 
inhabit waters that vary considerably 
in salinity (0 to 43 ppt) and tempera- 
ture (17° to 37°C; Zale and Merrifield, 
1989; Nichols 2 ). It is uncertain what 
affect these changing conditions have 
on the formation of growth zones in the 
otoliths, but periods of stress have been 
shown to halt otolith growth (Cam- 
pana, 1983). Furthermore, growth slows 
with age and growth zones become 
increasingly compressed, rendering oto- 
lith growth zones difficult to interpret. 
To circumvent the potential problems 
of otolith interpretation and to inde- 
pendently determine age, an applica- 
tion of the radiometric aging technique 
by using the 210 Pb: 226 Ra disequilibria 
in sagittal otolith cores (Campana et 
al., 1990) of Atlantic tarpon was per- 
formed, and the results are discussed 
in the context of existing estimated 
growth parameters. 
Materials and methods 
Pooled and individual otolith cores from 
Atlantic tarpon were analyzed for 210 Pb 
and 226 Ra to determine age. Annulus- 
derived age estimates were based on 
six independent otolith readings deter- 
mined by Crabtree et al. (1995) and 
resulted in a coefficient of variation 
of less than 12%. For radiometric age 
determination, otoliths were pooled into 
six groups based on annulus-derived age 
estimates, sex, and collection date. In 
addition, nine individual otoliths were 
analyzed. The age groups were selected 
to cover the full range of annulus-derived 
age estimates. Selected age groups had 
a narrow age range and members of the 
group were collected within a 6-month 
period. Otoliths of adult age groups were 
cored to the first two years of growth 
and otoliths of the youngest age groups 
1 Pamper, K. 1999. Personal commun. 
John G. Shedd Aquarium, 1200 S. Lake- 
shore Dr., Chicago, IL 60605. 
2 Nichols, K. M. 1994. Age and growth of 
juvenile tarpon. Megalops atlanticus , from 
Costa Rica, South Carolina and Venezu- 
ela. Senior thesis, Univ. South Carolina, 
Columbia, SC 29208, 52 p. 
