Schwenke and Buckel: Age, growth, and reproduction of Coryphaena hippurus 
85 
Table 1 
Monthly mean (±SE) fork length (FL; mm), FL range, and sample size (n) for male and female dolphinfish (Coryphaena hippurus) 
collected from May 2002 through May 2004. Sex was unable to be determined for six dolphinfish and their size information is not 
shown here. No dolphinfish were caught in December. SE = standard error. 
Male 
Female 
Mean FL (SE) 
FL range 
n 
Mean FL (SE) 
FL range 
n 
January 
682 (81.1) 
559-835 
3 
708(70.3) 
575-966 
5 
February 
— 
— 
0 
699(62.4) 
545-850 
4 
March 
709 (61.3) 
453-915 
6 
730 (17.9) 
560-889 
20 
April 
820(26.1) 
550-1130 
24 
773(12.1) 
608-1020 
50 
May 
935 (17.4) 
582-1315 
92 
765 (14.2) 
485-1275 
101 
June 
1123 (25.4) 
552-1395 
72 
688 (31.8) 
295-1145 
43 
July 
705(50.9) 
395-1451 
31 
607 (25.5) 
205-980 
48 
August 
805(41.5) 
310-1333 
46 
650(24.1) 
295-1205 
101 
September 
689 (51.0) 
462-1280 
16 
510(19.8) 
278-800 
40 
October 
594(25.6) 
432-798 
17 
556(26.1) 
410-1435 
41 
November 
570(50.0) 
520-620 
2 
628(60.7) 
460-905 
7 
from 205 to 1435 mm (mean length and weight of all 
females sampled was 655 mm FL [SE = 9.0] and 3.13 kg 
[SE = 0.2]; Table 1). There were significant differences in 
male dolphinfish mean weight (Kruskal-Wallis ANOVA: 
X 2 =80.6, df=9, P<0.001) and fork length (% 2 =98.9, df=9, 
P<0.001) by month (pooled over 2002-04). There were 
also significant differences in the mean weight of female 
dolphinfish (Kruskal-Wallis ANOVA: % 2 = 85.1, df=9, 
PcO.OOl) and fork length (x 2 =140.0, df=10, P<0.001) by 
month (pooled over 2002-04). 
Age and growth 
Because of the small size and complex structure of 
dolphinfish sagittae, counts were typically made on the 
dorsal side of the otolith as that region was the easiest 
to follow a clear increment sequence (Massuti et al., 
1999). Alternating light and dark bands, assumed to 
be daily increments (see Methods section), varied in 
width; tightly packed increments were located more 
toward the core and outer edge of the sagittae, and wider 
increments were located more in the center of the dorsal 
wing (see Massuti et al., 1999, for a picture of growth 
increments). 
A total of 181 dolphinfish otoliths were examined 
(u = 131 age-0 otoliths, n = 50 >age-0 otoliths). Annual 
marks could not be detected in transverse cross-sec- 
tions of sagittal otoliths of >age-0 dolphinfish. Daily 
increment counts were possible for a total of 107 (82%) 
otoliths from age-0 dolphinfish (designated age-0 be- 
cause of a lack of annual marks on scales [see be- 
low]). Of these, 62 were from female dolphinfish (mean 
FL = 509; range: 278-650 mm) and 39 were from males 
(mean FL = 538; range: 310-650 mm). Sex could not be 
determined for five of the smallest dolphinfish whose 
sagittae were examined (mean FL=152; range: 89-285 
mm) and was not recorded for one of the larger dol- 
phinfish aged from daily growth increments (FL = 575 
mm); however, these dolphinfish were still used in the 
von Bertalanffy analyses. Four of the 131 otoliths from 
age-0 dolphinfish were rejected because percent agree- 
ment between the first and second count exceeded 10%, 
and 20 age-0 otoliths were unreadable because of prob- 
lems with cross-sectioning or polishing. Minimum and 
maximum age estimates ranged from 31 to 204 days. 
Average growth rates based on daily ring counts were 
3.78 mm FL/day for all age-0 fish less than 650 mm 
FL. 
Scales were collected from 560 fish; 14 of the result- 
ing scale impressions were unreadable and five more 
were discarded because of uncertainty in the determi- 
nation of age (i.e., the three counts did not agree with 
each other). A total of 234 scales were classified as age- 
1 or older (84 females, 150 males) and the remaining 
scales (n = 307) were estimated to be age-0. The >age-0 
dolphinfish were classified as follows: 175 age-1 dol- 
phinfish ranging from 575 to 1435 mm FL (mean=938 
mm, SE = 9.8), 46 age-2 dolphinfish ranging from 925 
to 1451 mm FL (mean = 1197 mm, SE = 17.3), and 13 
age-3 dolphinfish ranging from 1095 to 1334 mm FL 
(mean=1249 mm, SE = 17.9). Final agreement between 
readings by the same investigator was 99%; an inde- 
pendent reader who was trained to identify annual 
marks on dolphinfish scales examined a subsample of 
50 >age-0 dolphinfish scales, and agreement between 
the independent reader’s reading and the first reader’s 
final age was 69% (Schwenke, 2004). 
Marginal increment widths from age-1 dolphinfish 
(rc = 182) were greatest in May, June, and July, dropped 
slightly in August, then dropped considerably during 
