1. Reproduction, Age and Growth of Sheepshead, Archosargus probatocephalus, in Mississippi Waters
Nancy J. Brown-Peterson1, James R. Warren2, William Dempster2, Gary Gray2 and Jason Tilley2
1Department of Coastal Sciences and 2Center for Fisheries Research and Development, The University of Southern Mississippi, Ocean Springs, MS
Sheepshead, Archosargus probatocephalus, commonly occur in estuarine and offshore waters of Mississippi and are regularly targeted by fishermen. Sheepshead (N=150) were collected monthly using hook and line from December 2003 – November 2004 in Mississippi waters to assess their reproduction, age and growth. Sheepshead ranged from mm TL (230-3,006 g) and 0–6 years, with age 4 fish most common in our samples. There was a highly variable but significantly positive distribution of lengths at age (p=0.01, r2=0.57). Males are longer at a given age than females, and the vonBertalanffy growth equation (based on size and age of fish sampled) predicts a larger maximum size for male sheepshead. All females <294 mm TL were immature, although 33% of age 1 females were sexually mature. The smallest male examined histologically (293 mm TL, age 1) had spermatozoa in the testis. Ovarian maturation began in December, and GSI values of females increased in February, peaked in March and returned to low levels by May. Females are capable of multiple spawns, and most females captured during March and April were undergoing final oocyte maturation. Mean batch fecundity estimates are 219,100 ± 36,700 eggs/female (N=7), and there was no significant relationship between batch fecundity and TL or weight (p>0.05). Our preliminary data suggest the Mississippi sheepshead population appears to be younger, more fecund, and reaches sexual maturity sooner than sheepshead sampled during in Louisiana.
ABSTRACT
AGE AND GROWTH
REPRODUCTIVE BIOLOGY
SUMMARY
Female sheepshead are heavier at a given size than males.
Otolith ring deposition occurs annually in late spring.
Sheepshead in Mississippi range from 0-6 years; age 4 fish were most common. There is a large variation in size at age for both sexes.
Males are longer than females at a given age and reach a larger maximum size.
Mississippi sheepshead appear to have a shorter life span than those from South Carolina, Florida and Louisiana.
All males examined were sexually mature; females reach 100% sexual maturity by age 3.
Sheepshead spawn in Mississippi waters during March and April.
Females spawn multiple times during the reproductive season; histological evidence suggests some are capable of daily spawning.
There is no relationship between batch fecundity and female size; mean batch fecundity is 219,100 eggs/female; mean relative fecundity is 214 eggs/g ovary-free body weight.
Mississippi males and females reach sexual maturity at a younger age than Louisiana and Florida sheepshead, and Mississippi females are more fecund than Louisiana females.
Additional data are necessary to confirm the above conclusions.
Figure 5. Monthly GSI values (mean ± SE) of male and female sheepshead
Figure 2. Length-weight relationships of sheepshead
W = 2.2x10-5 * TL2.958
r2 = 0.98
N = 80
W = 3.787x10-5 * TL2.865
r2 = 0.97
N = 70
Figure 3. Monthly marginal increments (mean ± SE) of age 4 sheepshead otoliths. N = 52. HO
FOM
Figure 8. Histological section of a female sheepshead in the FOM maturation class. CA—cortical alveolar oocyte; FOM—oocyte in lipid coalescence stage of FOM; HO—hydrated oocyte; Ygl—yolk globular oocyte; Ygn---yolk granular oocyte. CA
Ygn
Ygl
Sheepshead have a relatively short reproductive period. GSI values of both males and females are elevated from February – April, with a peak in March (Figure 5). This corresponds to previous reports of a February-April spawning season in Louisiana (Render and Wilson 1992) and spawning in March and April in Georgia (Music and Pafford 1984).
Female sheepshead ranged from 234 – 548 mm TL (230 – 3,006 g). Male sheepshead were similar in size, ranging from mm TL (235-2,495 g). Both sexes showed a significant, positive relationship between length and weight (Figure 2). Females tend to be heavier at a given size than males. Marginal increment analysis was conducted on otoliths from age 4 sheepshead (N=52) to validate the formation of annular rings. A minimal clear zone, suggesting recent deposition of a ring, was observed in May and August (Figure 3), although these were also months with greatest variability. Marginal increment analysis of age 3 (N=46) also showed a minimum in May. Additional data are necessary to verify annular formation of opaque bands in sheepshead otoliths, but these preliminary data suggest a ring is laid down once a year in May. Thus, we assume that age is equivalent to the number of rings on an otolith. Marginal increment analysis of sheepshead in Louisiana (Beckman et al. 1991) and South Carolina (Wenner 1996) indicated formation of a single annulus in the spring (April-May), similar to our findings.
Sheepshead, Archosargus probatocephalus
Sheepshead have asynchronous oocyte development (Figure 8), suggesting females can spawn multiple times during the 2 month spawning season. Some females with hydrated oocytes also had a second batch of oocytes in the lipid coalescence stage of final oocyte maturation (Figure 8), indicating the species is capable of daily spawning. Render and Wilson (1992) reported spawning frequency of sheepshead from Louisiana ranged from every 1 to every 20 days. No evidence of POFs were found in any females in the late maturation (LM) or FOM classes, although only 12 females in these classes were captured during this study. All hydrated females were taken from the offshore barrier islands, supporting previous suggestions that sheepshead primarily spawn offshore (Music and Pafford 1984; Render and Wilson 1992)
Figure 6. Percentage of male sheepshead in testicular maturity classes by month
Histological evidence of gonadal recrudescence in male sheepshead occurrred as early as October with the presence of fish in the early maturation (EM) class (Figure 6), and males in late maturation (LM) were observed as early as December. Histological evidence of sperm in the ducts was found December – May, although running ripe males were only captured in March, corresponding to the GSI peak (Figure 5). No immature males were observed in the sample; the smallest male examined histologically (293 mm TL, age 1) had spermatozoa in the testis. Nearly all Florida males are also sexually mature by age 1 (Murphy and MacDonald 2000). In contrast, Render and Wilson (1992) found males did not reach 100% maturity until age 4.
OBJECTIVES
Life history information on sheepshead in the northern Gulf of Mexico is limited to data collected in The objective of this study is to provide updated information on length-weight relationships, age, growth, reproductive seasonality and fecundity of sheepshead in Mississippi waters.
Lmax = 424
K = 0.633
t0 =
Lmax = 456
K = 0.409
t0 =
Figure 4. Age-length relationships of sheepshead
LITERATURE CITED
Beckman, D.W., A.L. Stanley, J.H. Render and C.A. Wilson Age and growth-rate estimation of sheepshead Archosargus probatocephalus in Louisiana waters using otoliths. Fish. Bull 89:1-8.
Murphy, M.D. and T.C. MacDonald An assessment of the status of sheepshead in Florida waters through Florida Marine Research Institute, St. Petersburg, FL. 50 p.
Music, J.L., Jr. and J.M. Pafford Population dynamics and life history aspects of major marine sportfishes in Georgia’s coastal waters. GA Dept. Nat. Res., Coastal Res. Div., Coastal Fish Section, Final Report. Study IV Federal Aid Project F p.
Render, J.H. and C.A. Wilson Reproductive biology of sheepshead in the northern Gulf of Mexico. Trans. Am. Fish. Soc. 121:
Wenner, C.A Age and growth of sheepshead, Archosargus probatocephalus, from Wouth Carolina waters with some preliminary management concepts. SC Dept. Nat. Res. Final Report, job 6 of F p.
Sheepshead were collected monthly using hook and line from December 2003 through November 2004 in Mississippi waters, including inshore bays and bayous and near offshore barrier islands. Otoliths were removed, sectioned on an isomet saw and opaque bands were counted under a microscope for age-growth analysis. Gonads were removed, weighed and preserved in 10% neutral buffered formalin for histological analysis. Ovaries of fish undergoing FOM with hydrated oocytes were preserved in Gilson’s fixative and fecundity was determined using the volumetric method.
METHODS
r2 = 0.37
p = 0.14
Figure 9. Relationship between batch fecundity and TL
Figure 7. Percentage of female sheepshead in ovarian maturity classes by month
Histological evidence of gonadal recrudescence in female sheepshead was first seen in December, with fish in the early maturation (EM) class (Figure 7). Females in spawning condition (FOM class) were only found in March and April, corresponding to the GSI peak (Figure 5). Regressed females were found during all months except the time of elevated GSI values (February – April). All females <294 mm TL were immature, and all females >353 mm TL were sexually mature. The majority of age 1 (67%) and age 2 (75%) females were immature; all females ages 3-6 were sexually mature. In contrast, female sheepshead in Louisiana and Florida did not reach 100% sexual maturity until age 5 (Render and Wilson 1992; Murphy and MacDonald 2000). There are insufficient data to accurately determine size or age at 50% maturity for females in Mississippi.
RESULTS
Figure 1. Number of sheepshead captured each month in Mississippi waters.
N=80 Females
N=70 Males
There was no relationship between fish size and batch fecundity (Figure 9). Batch fecundity estimates of 7 fish ranged from 144,010 – 363,321 eggs, with mean batch fecundity of 219,100 ± 36,700 eggs/female. This is greater than batch fecundity reported for 20 Louisiana females, which ranged from 1,100 – 250,000 eggs with a mean of 47,000 (Render and Wilson 1992). Mean relative fecundity of Mississippi fish is 214 ± 42 eggs/g ovary-free body weight.
Sheepshead ranged from 0 to 6 years, with age 4 fish most common in our samples. Mississippi sheepshead appear to be much younger than sheepshead from other areas, based on maximum ages of fish collected in South Carolina (26 years; Wenner 1996), Louisiana (20 years; Beckman et al. 1991) and Florida (13-16 years; Murphy and MacDonald 2000). There was a highly variable but significantly positive distribution of lengths at age for both sexes (p = 0.01, r2 = 0.50, males, r2 = 0.38, females; Figure 4). The large variability in size at age is common for sheepshead, and has been reported for South Carolina, Florida and Louisiana. Males were longer than females at a given age, and the vonBertalanffy growth equation predicts a larger maximum size for male sheepshead than females (Figure 4). These results are in contrast to findings from Louisiana (Beckman et al. 1991), where females were predicted to be larger than males, although estimated Lmax for males from both areas are the same. However, K values suggest that Mississippi females exhibit more rapid growth to an asymptotic size than males.
ACKNOWLEDGMENTS
This research was funded by the U.S. Fish and Wildlife Service, Sportfish Restoration Program, through the Mississippi Department of Marine Resources.