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Fishery Bulletin 115(3) 
140 1 A 
120 - 
100 
100 200 300 400 500 600 700 
Oocyte diameter (pm) 
Oocyte diameter (|jm) 
Figure 6 
Distributions of oocyte sizes of female Gulf menhaden 
( Brevoortia patronus) collected from the northern Gulf 
of Mexico during 2014 through 2016, showing an inde- 
terminate fecundity pattern with lack of recruitment of 
secondary vitellogenic oocytes at the end of the spawn- 
ing season. (A) Fish captured 31 October 2014, 186 mm 
FL. Arrow indicates oocytes undergoing oocyte matura- 
tion; only oocytes >500 pm were counted for fecundity 
estimates. (B) Fish captured 18 March 2015, 165 mm 
FL. Note lack of vitellogenic oocytes from 80 to 350 pm 
in the March sample. 
how these new data address critical needs for stock 
assessments and for understanding the ecological dy- 
namics of the stock. The results of our work indicate 
that Gulf menhaden have greater fecundity than that 
previously reported, and the characteristics of the re- 
productive dynamics are different than previously 
thought. Specifically, we found that egg production is 
greater and that the reproductive season is protracted, 
lasting 5.5-months. We also found that Gulf menhaden 
are batch spawners that spawn every 2. 1-4.3 days and 
that although they show indeterminate fecundity, they 
have several traits typically associated with determi- 
nate fecundity. 
The 5.5-month reproductive season (October-March) 
for Gulf menhaden from the north-central GOM de- 
scribed here is slightly longer than that previously 
reported. Combs (1969) found the spawning season oc- 
curred from late October to February or early March 
according to histological analysis, whereas Lewis and 
Roithmayr (1981) found peak spawning, determined 
from GSI, to occur from November through January, 
and that a few spawning capable females were present 
in February and none after that time. Not only is the 
Gulf menhaden spawning season longer than previous- 
ly reported, our data indicate that a high percentage of 
fish are spawning in October, and these fish are vulner- 
able to capture by the commercial purse-seine fishery 
that operates through the end of October. 
Smaller and younger Gulf menhaden have a shorter 
reproductive season than older, larger fish. Although 
data were not previously available for size-at-sexual- 
maturity for Gulf menhaden, sexual maturity was as- 
sumed to have been reached when fish approach their 
second birth date (VanderKooy and Smith 1 ). Indeed, we 
found that 50% maturity is reached at 137-140 mm FL, 
and fish of this size are found in the fall as they ap- 
proach their second birth date. However, smaller age-1 
fish in the fall have lower GSI values and delayed go- 
nadal development than those of larger fish. Further- 
more, our analysis of historic Gulf menhaden data sug- 
gests that the reproductive season may have shifted to 
a slightly earlier start in 2014 than during 1964-1970, 
possibly as a result of 2014 fish being slightly larger 
and in better condition. It is well established that old- 
er, larger females begin spawning earlier in the repro- 
ductive season and that smaller individuals may have 
a longer time between spawning events than larger in- 
dividuals of the same species (Lowerre-Barbieri et al., 
2011; Fitzhugh et al., 2012). These variations among 
different-size fish must be taken into account when 
calculating annual fecundity estimates and estimating 
spawning stock biomass. Our analysis has taken this 
variation into account by including a 1-month delay in 
the spawning season for age-1 fish, although we have 
insufficient data to estimate differences in spawning 
frequency between females age-1 and older. 
This study is the first to examine GSI and histol- 
ogy of male Gulf menhaden. Males began gonadal re- 
crudescence about 1 month before females do but, like 
females, were reproductively inactive by mid-April. 
Male Gulf menhaden exhibit an anastomosing tubular 
type of testes typical of other clupeids (Grier and Uribe 
Aranzabal, 2009). Male and female GSI values were 
similar in Gulf menhaden, particularly at the begin- 
ning of the spawning season, as also seen in another 
clupeid, the Pacific sardine ( Sardinops sagax [Stewart 
et al. 7 ]). In contrast, some male sardines have higher 
GSI values than females (Tsikliras and Antonopoulou, 
2006; Tsikliras et al., 2010), although male marine te- 
7 Stewart, J., G. Ballinger, and D. Ferrell. 2010. Review of 
the biology and fishery for Australian sardines ( Sardinops 
sagax) in New South Wales — 2010. Industry & Investment 
NSW, Fish. Res. Rep. Ser. 26, 57 p. [Available from website.] 
