Schwenke and Buckel: Age, growth, and reproduction of Coryphaena hippurus 
91 
Reproduction 
Peak spawning in dolphinfish off the southeastern 
United States extends from January through July 
(Beardsley, 1967; this study). Previous reviews of the 
reproductive characteristics of dolphinfish revealed 
that young dolphinfish are throughout the year in 
the Florida current and their presence may indicate 
year round spawning there (Oxenford, 1999). However, 
there are regional peaks in spawning activity off the 
southeastern U.S. coast. Peaks occur from January to 
March in Florida (Beardsley, 1967) and from May and 
June (Schuck, 1951) or June and July (Rose, 1966) 
in North Carolina. Unfortunately, sampling in North 
Carolina was limited to May and June in the former 
study (Schuck, 1951) and June, July, and August in 
the latter study (Rose, 1966). Based on our nearly year 
round collections of gonad weights, peak spawning in 
dolphinfish occurs from May to July off the coast of 
North Carolina; interestingly, peak spawning (deter- 
mined from GSI values) occurs from May to June in 
Barbados (Oxenford, 1985). 
Back-calculated hatching dates of age-0 fish collected 
in North Carolina confirm a spawning period from Jan- 
uary through July off the southeastern United States; 
hatching dates do occur in other months, but at lower 
levels. Similarly, there is good correspondence between 
dolphinfish spawning and back-calculated hatching 
dates for the Mediterranean Sea (Morales-Nin et al., 
1999). There is interannual variation in the hatching- 
date distribution of dolphinfish (Massutf et al., 1999; 
this study); this may be due to changes in the spawning 
peak or to differential mortality (Massutf et al., 1999). 
Given the lack of information on dolphinfish mortality, 
corrections for mortality in hatching-date distributions 
were not made. 
The assignment of a 15 April biological hatching date 
to all >age-0 dolphinfish in this study reduces much of 
the variability associated with length-at-age seen in 
the von Bertalanffy growth curve where a biological 
hatching date is not used. Some variability in length- 
at-age still exists, however, and may be a result of other 
environmental factors experienced by an individual 
dolphinfish (i.e., water temperature, differences in prey 
consumption and prey quality). However, the protracted 
spawning season is likely the most important factor 
responsible for variability in length-at-age. 
Overall, there has been little evidence of changes 
in size-at-maturity in dolphinfish off the U.S. east 
coast from the 1960s to the time of our study. Males 
first begin to mature at a fork length of about 435 
mm, which is in agreement with Beardsley’s (1967) 
observation of first maturity in males at a fork length 
of 427 mm. A previous estimate of the length at 50% 
maturity for female dolphinfish caught off Florida in 
the 1960s (Beardsley, 1967) is nearly identical to our 
estimate (450 [Beardsley, 1967] vs. 457 mm FL [our 
study]); however, Beardsley (1967) found earlier first 
maturity in females (-350 mm FL) compared to our 
study (-430 mm FL). 
Summary and implications 
Age, growth, and reproduction data for dolphinfish 
caught off the coast of North Carolina are provided. 
Using scale annual marks and daily growth increments 
from otoliths, we determined an updated age-length 
function. Furthermore, comprehensive seasonal esti- 
mates of gonad weights and marginal increment widths, 
as well as back-calculated hatching dates and daily 
growth-rate estimates, are the first for dolphinfish in 
North Carolina waters. Because this species is highly 
migratory, a much broader study encompassing the U.S. 
east coast or western North Atlantic may be needed in 
order to truly characterize dolphinfish reproduction and 
marginal increment widths. Direct validation through 
mark and recapture studies could also confirm annual 
marks on scales and provide good estimates of growth 
rates for tagged dolphinfish that remain at large through 
suspected periods of annulus deposition. 
Intense positive size-selective mortality can lead to 
changes in life history parameters (Pitcher and Hart, 
1982; Conover and Munch, 2002). However, there have 
been no changes in size-at-age or size-at-maturity of 
dolphinfish; therefore, the increased harvests in the 
1980s and 1990s have not influenced these life history 
parameters to date. Because of their fast growth rates 
and small size-at-maturity, dolphinfish appear an ideal 
fishery resource species capable of withstanding high 
rates of fishing mortality. 
Acknowledgments 
We thank Captain J. Gay of the FV Old Smokey for 
his field assistance, R. Gregory and L. Daniel from 
North Carolina Division of Marine Fisheries for dis- 
cussions and use of equipment, and J. Arnott and J. 
Edwards from Center for Marine Science and Technol- 
ogy (CMAST), North Carolina State University, for 
extensive help with dolphinfish sampling. We thank 
P. Rudershausen for his assistance with scale read- 
ings. P. Rudershausen, J. Hightower, and L. Stefanski 
reviewed an earlier draft of the manuscript. We also 
thank B. Morales-Nin, E. Massutf, and J. Moranta 
from the Mediterranean Institute for Advanced Stud- 
ies (IMEDEA) in Mallorca, Spain, D. Ahrenholz from 
the Center for Coastal Fisheries and Habitat Research, 
National Oceanic and Atmospheric Administration, in 
Beaufort, North Carolina, and S. Searcy from CMAST 
for their assistance with our otolith preparation tech- 
nique. This project was funded by a North Carolina 
Fishery Resource Grant no. 02-EP-01. 
Literature cited 
Beardsley, G. L., Jr. 
1967. Age, growth, and reproduction of the dolphin, Cory- 
phaena hippurus, in the Straits of Florida. Copeia 
1967:441-451. 
