Brown-Peterson et al.: Reproductive biology of Brevoortia patronus in the Gulf of Mexico 
285 
Relatively little recent work has been done to de- 
scribe the reproductive dynamics of Gulf menhaden. 
Gulf menhaden spawn offshore in high-salinity waters 
(Fore, 1970; Sogard et al., 1987). Larvae are transport- 
ed to estuaries from late winter through early spring 
(Shaw et al., 1985; Govoni, 1997), and juveniles re- 
main in the estuary until they move offshore the fol- 
lowing fall. Females in spawning condition have been 
documented to occur from September to April, but the 
reported peak spawning season occurs between De- 
cember and February (Combs, 1969; Lewis and Roith- 
mayr, 1981). Gulf menhaden are batch spawners (Lewis 
and Roithmayr, 1981), but the duration of the spawn- 
ing season, the frequency with which an individual 
spawns, and annual fecundity are not well known, but 
are likely age- and length-dependent (see Lowerre-Bar- 
bieri et al., 2011). Because accurate age-specific spawn- 
ing seasonality, batch fecundity (BF), and estimates of 
spawning frequency have not been reported for Gulf 
menhaden, the fecundity estimates reported by Lewis 
and Roithmayr (1981), currently employed in the stock 
assessment model used for Gulf menhaden, may be in- 
accurate. Such inaccuracies can lead to a biased un- 
derstanding of the reproductive capability of the stock. 
Our objective is to determine the characteristics of 
the reproductive biology of Gulf menhaden in order to 
assess their effects on stock assessments and to under- 
stand historical patterns of reproductive output. We 
provide information on the reproductive biology of Gulf 
menhaden, including size-at-maturity, the duration and 
timing of the spawning season, individual ovarian and 
testicular dynamics, BF, and spawning frequency, and 
incorporate age-specific fecundity data into an age- 
structured stock assessment model to understand how 
updated estimates can change our understanding of 
the Gulf menhaden stock. Finally, we evaluate historic 
changes in the demographic characteristics of the Gulf 
menhaden stock by comparing data collected from the 
commercial fishery from 1964 through 2014. This re- 
search is intended to improve a general understanding 
of the dynamics of the Gulf menhaden stock and pro- 
vide information for management. 
Materials and methods 
Collection of samples 
Gulf menhaden were collected from Mississippi and 
Louisiana coastal waters of the northern GOM from 
August to October 2014, from January to June 2015, 
November 2015, and from January to February 2016. 
Samples were obtained opportunistically from purse- 
seine boats at the Omega Protein reduction facility at 
Moss Point, Mississippi, during the commercial fish- 
ing season (from April to October) and from commer- 
cial shrimp trawls in February 2015. Gulf menhaden 
were also obtained during trawl and gillnet sampling 
by the Louisiana Department of Wildlife and Fisher- 
ies (LDWF) and the University of Southern Mississippi 
(USM) Center for Fisheries Research and Development 
(CFRD) in the winter and early spring. When possible, 
biological data were collected from fish within 24 h of 
capture from fresh fish stored on ice. All collections ob- 
tained from LDWF, and some collections from Omega 
Protein, were frozen upon capture, and these specimens 
remained fully or partially frozen during the recording 
of biological data. 
Fish were measured for fork length (FL) in milli- 
meters and weighed (W) in grams, and scales were re- 
moved from along the lateral line, below the insertion 
of the dorsal fin, rinsed, and stored in paper coin en- 
velopes for age determination, consistent with current 
fishery age-sampling methods. Sex was macroscopically 
determined, and gonads were removed and weighed 
(GW) to the nearest 0.01 g. The gonadosomatic index 
(GSI) and condition factor (K) were calculated as: 
GSI = (GW/(W - GW)) x 100 (1) 
and K = ( W/FL 3 ) x 100,000. (2) 
Gonads were macroscopically classified into reproduc- 
tive phases according to the terminology of Brown- 
Peterson et al. (2011), and a portion of the left gonad 
from each fish was placed into individually labeled cas- 
settes and preserved in 10% neutral buffered forma- 
lin for histological analysis. Gonadal tissue from fro- 
zen specimens was placed in cold (4°C) formalin and 
allowed to thaw in the refrigerator in the fixative to 
minimize damage to the frozen tissues and improve the 
histological preparations. 
Age determination 
Individual ages were determined by methods con- 
sistent with the Gulf menhaden stock assessments 
(VanderKooy 4 ). Collected scales were rinsed in warm 
tap water, dried, and mounted onto glass slides (n=10 
scales/fish). Age estimates were determined by count- 
ing annuli on images that were projected by using an 
Eberbach 5 macro-projector (Eberbach Corp., Ann Arbor, 
MI) at 48x magnification. A birthdate of 1 January was 
assigned for all fish (SEDAR 2 ). Fish captured in Janu- 
ary and February that had scales with a large margin 
beyond the last annulus were classified as a year older. 
Reproductive biology 
Histological processing of gonadal tissues followed 
standard techniques. Tissues were fixed for a minimum 
of 1 week, rinsed overnight in running tap water, de- 
hydrated in a series of graded ethanols, and embed- 
4 VanderKooy, S. (ed.) 2009. A practical handbook for deter- 
mining the ages of Gulf of Mexico fishes, 2nd ed. Gulf States 
Mar. Fish. Comm., Publ. No. 167, 136 p. Gulf States Mar. 
Fish. Comm., Ocean Spring, MS. [Available from website, ac- 
cessed June 2016]. 
5 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
