Schwenke and Buckel: Age, growth, and reproduction of Coryphaena hippurus 
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Figure 4 
Box plots of gonadosomatic indices (GSI) for (A) males and (B) female dolphinfish ( Coryphaena hippurus) collected from 
January 2002 through December 2004, and (C) mean (±SE) In (gonad weight) of male (closed circles) and female (open 
circle) dolphinfish adjusted to a common length for March through October of 2002-04. Like letters for each sex in C 
indicate no significant difference between months as determined with ANCOVA. The 25 th percentile of the GSI data is 
represented by the boundary of the box closest to zero, in relation to the y-axis, and the 75 th percentile is represented by 
the boundary of the box farthest from zero. The line within the box is the median value. Whiskers (error bars) above and 
below the box indicate the 90 th and 10 th percentiles, respectively. Outlying values for both upper and lower ranges are 
represented by closed circles (in A and B). SE = standard error. Sample sizes are given inside the boxes (in A and B). 
methods used to date. Massuti et al. (1999) using sagit- 
tal plane sections did not observe annual marks on dol- 
phinfish otoliths from the Mediterranean Sea, although 
the authors speculated that detection of annual marks 
on the outer edges of adult otoliths may have been hin- 
dered by otolith preparation. A transverse cross-section 
approach was used in our study in an attempt to obtain 
a view of the outer edges, but the technique used in 
otolith preparation or the complex structure of >age-0 
dolphinfish otoliths may have prevented detection of 
any annual marks. Alternatively, annual marks may 
not exist on sagittal otoliths of dolphinfish. 
Validation of scale annuli has been attempted in only 
a few studies of dolphinfish. Although the annual marks 
on scales of >age-0 dolphinfish were relatively easy 
to interpret and within-laboratory agreement of age 
assignments was good in our study, these features do 
not establish that the ages are correct. In general, the 
monthly pattern in marginal increment widths in our 
study was similar to prior work in Florida (Beardsley, 
1967). After measuring the distance between the last 
annulus and the margin of the scale for all dolphin- 
fish with one or more year marks, Beardsley (1967) 
considered November to be the period of annulus for- 
mation because of an abrupt decrease in width of the 
increments from October to November. The smallest 
mean marginal increment in our study occurred dur- 
ing winter; this finding supports the hypothesis that 
dolphinfish lay a new annulus in winter as a result of 
decreased water temperature. The temperature of the 
