Winner et al.: Age and growth of Archosargus probatocephalus in Tampa Bay, Florida 
157 
28°0'N 
27M5'N 
27°30'N 
Figure 1 
Sampling locations (indicated by black circles) in Tampa Bay, Florida, 
where sheepshead {Archosargus probatocephalus) were collected dur¬ 
ing 1993-2009 for age and growth analysis under the guidance of the 
Fisheries-Independent Monitoring program of the Florida Fish and 
Wildlife Conservation Commission. 
82°45'W 
82°30'W 
lith sections were mounted on microscope slides by 
using Histomount solution (Thermo Fisher Scientific, 
Waltham, MA). With a dissecting microscope (8-25x 
magnification), 2 or 3 readers independently counted 
the opaque rings on each otolith twice under reflected 
light. Readers counted rings without knowing the sex, 
length, or capture date of specimens. Disagreements 
in annulus counts were resolved by at least 2 read¬ 
ers, without knowledge of previous counts. If an an¬ 
nulus count could not be agreed upon after reexamina¬ 
tion, the otolith was rejected from the age and growth 
analysis. 
Validation of annuli counts was completed through 
marginal-increment analysis, which provided indi¬ 
rect evidence at the otolith margin of the periodicity 
of annulus formation. Measurements from the core to 
the proximal edge of each annulus, 
along the ventral sulcal ridge, were 
completed with a digital image- 
processing system for all otoliths 
processed from 1995 through 1998. 
The marginal increment was calcu¬ 
lated as a percentage by dividing 
the distance from the terminal an¬ 
nulus to the marginal edge by the 
distance between the last 2 annuli 
formed on the otolith and multiply¬ 
ing by 100. Monthly marginal-in¬ 
crement statistics (25th, 50th, and 
75th percentiles) with all age classes 
pooled were calculated for Febru¬ 
ary 1995-December 1998, the period 
during which monthly samples were 
collected consistently. Additionally, 
monthly marginal-increment sta¬ 
tistics were plotted, with months 
pooled across all years (1995-1998), 
for individual age classes (ages 1-6 
only). Fish age 7 and older were ex¬ 
cluded from these age-class-specific 
analyses because of low sample size 
across sampled months. 
Age of each sheepshead was calcu¬ 
lated on the basis of annulus count, 
marginal increment, date of cap¬ 
ture, and an assumed hatching date 
of 1 April (an assumption based on 
spawning and larval recruitment; 
Parsons and Peters, 1989; Tuck¬ 
er and Alshuth, 1997). Therefore, 
sheepshead collected in February 
and March that had recently formed 
an annulus, as determined by a low 
(<30%) marginal increment were as¬ 
signed an age of one less than the 
ring count. Fish collected in April, 
May, or June that were about to de¬ 
posit an annulus (at >80% marginal 
increment) were assigned an age of 
one more than the ring count. All 
other fish were assigned an age equal to the ring count. 
Daily age was calculated on the basis of the age and 
the number of days that had passed between 1 April 
and the date of collection: 
{integer age -i- number of days)/365. (1) 
The G-test was used to compare sex ratios for all fish 
collected and subsets of fish kept for or eliminated from 
the aging analysis. Lengths of retained and eliminated 
sheepshead were compared by using the KS 2-sample 
test (Proc Nparlway procedure; SAS, 2006). The KS 
test was also used to compare age-frequency distribu¬ 
tions between the sexes. 
The von Bertalanffy (1957) growth equation, 
4 = 
( 2 ) 
