Tranxaciionx of the American Fisheriex Society 124:37-54. 1995American Fisheries Society

Age, Growth, Mortality, and Reproductive Biology ofRed Drums in North Carolina Waters

JEFFREY L. Ross AND TONYA M. STEVENSNorth Carolina Division of Marine Fisheries

Post Office Box 1550. Manteo. North Carolina 27954. USA

DOUGLAS S. VAUGHANNational Marine Fisheries Service. Beaufort Laboratory

101 Fivers Island Road, Beaufort. North Carolina 285/6-9722. USA

Abstract.—Red drums Sciaenops ocellatus were sampled in North Carolina waters from October1987 through December 1990. Ages determined from sectioned otoliths were validated by length-frequency and marginal-increment analyses, and the recapture of oxytelracycline-marked fish. Fishgrowth was rapid during the first 5 years, after which annual growth increments were much smaller.Growth was best described by a continuous double von Bertalanffy growth curve, with a transitionage of 4.4 years; K\, the growth coefficient for fish younger than the transition age, was 0.30/yearand KS' lne growth coefficient for fish older than the transition age, was 0.07/year. Maximumobserved age and size were 56 years and 1.250 mm fork length (FL) for males and 52 years and1,346 mm FL for females. Fifty-percent maturity was attained among males by age 2 at 621-640mm FL and among females by age 3 at 801-820 mm FL. Spawning occurred from August throughearly October in cstuarinc waters of Pamlico Sound and nearshore ocean waters close to barrierisland inlets. Commercial and recreational landings increased during the 1980s, with most of theharvest composed of immature, age-1 fish caught during the fall. Unadjusted annual return rates(18-25%) for lagged juveniles were high. Annual survival rates based on tag-recapture data wereonly 6-24%, and estimates of instantaneous total mortality rates (Z) from cohort-based catchcurves were 1.56-2.88 for the 1985-1988 year-classes. The relative abundance of 20-55-year-oldred drums has declined 90% since 1968-1972.

The red drum Sciaenops ocellatus is an estua-rine-dependent species, occurring from Massachu-setts to Key West, Florida, on the U.S. Atlanticcoast and from southwest Florida to northern Mex-ico in the Gulf of Mexico (Lux and Mahoney 1969;Mercer 1984). Red drums supported a commercialfishery during the 1930s as far north as New Jer-sey, but since 1950 annual landings north of Vir-ginia have been less than 1 metric ton (Mercer1984). Currently, commercial fisheries along theAtlantic coast are virtually nonexistent, except inNorth Carolina. Florida has prohibited the sale ofred drum. South Carolina recently established itas a game fish, and Georgia regulations prohibitthe taking of red drum with nets (SAFMC 1990).Strict regulatory measures have been enactedthroughout the Gulf of Mexico to reduce the like-lihood of overfishing (Murphy and Taylor 1990).

Red drums are sought by recreational anglersthroughout North Carolina's coastal waters. Thesurf and inlets from Oregon Inlet to Cape Lookoutand the shoals and river mouths in Pamlico Soundsupport a trophy fishery that has produced 10 ofthe 16 current world records; 8 of the 10 recordfish exceeded 25 kg. The current all-tackle record

red drum (43 kg) was caught from the HatterasIsland surf (IGFA 1992).

Red drums attain their largest reported sizes inNorth Carolina, but we found no published ageand growth research for these waters. Similarly,collections of juvenile red drums in North Carolinaindicated that spawning occurs during summer andearly fall (Weinstein 1979; Mercer 1984), but de-tailed information on reproductive biology is un-available. Along the Atlantic coast, red drumgrowth has been described in Georgia (Pafford etal. 1990), South Carolina (Wenner et al. 1990),and Florida (Murphy and Taylor 1990); spawningseasonality and maturity have been described forSouth Carolina (Wenner et al. 1990) and the eastcoast of Florida (Murphy and Taylor 1990). In thispaper, we validate an aging procedure and describeage and growth, maturity schedules, and spawningseasonality for red drum in North Carolina waters.

High mortality and tag-return rates have beenreported for Georgia, Florida, and South Carolina(Music and Pafford 1984; Murphy and Taylor1990; Wenner et al. 1990). Stock assessments forthe southern Atlantic coast have indicated that sub-adult red drums are overfished (Vaughan and Hel-

37

SEDAR 18-RD46

38 ROSS RT AL.

• DMF tagging sites® DMF/commercial venture tagging areas

FIGURE 1.—Locations in coastal North Carolina where red drums were collected or lagged and released during1986-1990 (DMF is Division of Marine Fisheries).

ser 1990; Vaughan 1992). Therefore, in this paperwe also address the si/e and age composition andexploitation patterns of the recreational and com-mercial fisheries, and describe mortality rates ofred drums in North Carolina waters.

MethodsAge and growth.—Red drums were collected

from October 1987 through December 1990throughout North Carolina coastal waters. Mostcollections were from Pamlico Sound and its trib-utaries, and from the surf and inlets of the OuterBanks between Oregon Inlet and Cape Lookout(Figure 1). Red drums were captured by hook andline, gill nets, pound nets, commercial trawls, andlong haul seines. Fork length (FL, mm) was re-corded for all fish and is used for all lengths men-tioned in text unless otherwise noted. Total length(TL) was recorded in 1989 and 1990, and wholeweight (ViO to the nearest 0.1 kg was obtained whenpossible.

Otoliths (sagittae) were excised and stored dry.A Buehler Isomet low-speed saw with diamondwafering blades was used to cut 0.4-0.7-mm-thicktransverse sections of the sagittae through the core.Sections were mounted on a microscope slide withAccu*mount mounting medium. Sections wereread by two authors independently by means of adissecting microscope (20X magnification) with

reflected light; a common reading was conductedto resolve differences.

Validation of ages from otoliths followed threecriteria provided by Bagenal (1978). The percentoccurrence of opaque margins on otoliths was plot-ted by month to determine the timing of annulusformation (Beckman et al. 1989). Red drums (N= 118) captured with hook and line were injectedwith oxytetracycline (OTC; 25 mg/kg bodyweight), tagged, and released from 1988 through1990. Sections of the sagittae from recapturedOTC-marked fish were viewed under ultravioletlight to determine how many opaque zones weredeposited since the time of release. Finally, month-ly length-frequency modes were compared tolengths of otolith-determined age-groups.

The ages of red drums were adjusted becausethe first annulus formed 19-21 months after theactual hatching date. September 1 was used as abiologically realistic birthdate because it was themidpoint of the peak-spawning period. Ages wereincremented 1 year on this date.

Growth of red drums was described by fitting acontinuous double von Bertalanffy growth curveto data by a nonlinear, iterative, least-squares ap-proach (Vaughan and Helser 1990). The model wasfit to observed lengths at age for 839 red drumsby means of the PROC NLIN procedure with Mar-

SEDAR 18-RD46

RILD DRUM BIOLOGY 39

quardt option (SAS Institute 1987). Each age wasadjusted to account for the month of capture basedon a September 1 birthdate: for example, fish cap-tured in October were considered 1/12 year olderthan their assigned otolith age. A weightingscheme, based on the inverse of sample si/e foreach age, was used to decrease the impact of largesample sizes of young fish.

Reproductive hiology.—Gonads from 805 reddrums were excised and stored in 10% bufferedformalin from 1988 through 1990. Before exam-ination, gonads were removed from the preser-vative, washed, and blotted dry. Sex was deter-mined and gonads were weighed to the nearest 0.1g. Ovaries and testes were staged macroscopically,and stage confirmation was made by histologicalexamination of 29% of the gonads. Medial sectionsof preserved gonadal tissue were transferred to50% isopropyl alcohol, processed through a Tech-nicon Duo II tissue processor, and blocked in par-affin. Sections (7 jxm thick) were cut from eachgonad with a rotary microtome, stained with Har-ris's hemaloxylin. and counter-stained with eo-sin Y.

Characteristics of the developmental stageswere based on the macroscopic and histologicalfeatures described by Murphy and Taylor (1990),but modified by merging their "immature" and"resting virgin" stages into a stage called "im-mature," and their "spent" and "recovering"stages into a stage called "spent." The develop-mental stages are thus: (1) immature, (2) maturing,(3) well developed (mature), (4) ripe (gravid), (5)partially spent, (6) spent, and (7) resting. Maturefish were those in stages 3-7.

Gonadosomatic index (GSI) was calculated byusing the formula: GSI = (GW/FL3)100, whereGW = preserved gonad weight (g) and FL = forklength (cm). Because many of the samples wereobtained from filleted carcasses, fork length wasused instead of body weight to develop a GSI. TheStatistical Analysis System (SAS Institute 1985)was used for maximum-likelihood analysis(PROBIT) to generate 50% maturity schedules.

Tag-recapture data.—In all, 3.002 red drumswere tagged and released in estuarine waters from1986 to 1990. Fish were captured in commercialpound nets, anchored gill nets, and runaround gillnets set in Pamlico Sound grass flats adjacent toHatteras and Ocracoke islands and in the Pamlico,North, and New rivers (Figure I). All healthy reddrums were measured, tagged, and released. Fishranged from 223 to 880 mm, but 98% were 220-500 mm (10-15 months old). In 1986, Floy cinch-

up lags and Floy internal anchor tags were used,after which only Floy internal anchor tags wereused. Tags were uniquely numbered and includeda legend indicating that a reward would be givenfor tags returned to the North Carolina Divisionof Marine Fisheries (DMF). Internal anchor tagswere inserted into a small abdominal incision madeabove the midventral line, just beyond the poste-rior extension of the pelvic fin. Cinch-up tags wereinserted dorsally and just posterior to the termi-nation of the second dorsal fin.

Fishery ami mortality rates.—Data for red drumcatches in North Carolina were obtained from sev-eral sources: fishery-specific length frequenciesfrom the DMF biological database (1979 to pres-ent); commercial landings from the North CarolinaGeneral Canvas Data compiled through the DMFand National Marine Fisheries Service (NMFS)cooperative data collection program (1970 to pres-ent); and length-frequency and catch-per-unit-ef-fort (CPUE, catch/trip) data for recreational catch-es from the North Carolina Marine RecreationalFisheries Statistics Survey (MRFSS; 1987-pres-ent).

The Seber (1970) and Robson and Youngs(1971) tag recovery model was selected to estimatea series of survival rates from a sample of fishcaptured, tagged, and released into the populationat roughly the same time each year for five con-secutive years (Ricker 1975). To fit the model, onlyfish of the previous year's cohort that were taggedfrom July through December were included; thiswas also the period for first-year recoveries; suc-ceeding recovery periods were the entire year. Thenumber of recaptured fish per year was adjustedfor nonreporting, tagging mortality, and tag loss.Cohort-specific survival (S) and exploitation rates(u) were estimated with the computer program ES-TIMATE, which uses the maximum-likelihoodmethod for estimating parameters (Brownie el al.1985).

Total mortality (Z) was also estimaled by catchcurve analysis (Ricker 1975). Annual calch inweighl was converted to annual catch in numbersat age by the use of length-frequency data by yearand gear and annual age-length keys for 1986-1990. Catch in weight was converted to catch innumbers based on mean weighl of red drums es-limated from length-frequency data. Catch esti-mates (both commercial and recrealional) and rec-realional length-frequency data represented NorthCarolina and Virginia (>95%> from North Caro-lina). Ages 0-5 were included; age 6+ was createdby pooling ages 6 and older. Cohort-specific total

SEDAR 18-RD46

40 ROSS ET AL.

100

Jan Fab Mar Apr May Jun Jul

MonthSap Oct Nov Dac

FIGURE 2.—Monthly percent occurrence of opaque zones on the margins of red drum otoliths from North Carolinawaters, 1987-1990. Total monthly sample sizes ranged from 0 to 251 (sample sizes were less than 10 in Januaryand February).

mortality rates were calculated for the 1985-1988year-classes. Thus, Z for the 1985 year-class wasbased on catches of age-1-5 fish from 1986through 1990, whereas Z for the 1988 year-classwas based only on catches of age-1-2 fish during1989-1990. Red drums were considered fully re-cruited to both fisheries at age 1. The methods ofBoudreau and Dickie (1989) and Pauly (1979)were used to estimate natural mortality (Af).

ResultsAge. Growth, and Size and Age Composition

We collected sagittae from 843 red drums (250-1,346 mm) from 1987 through 1990. Sections hadwell-defined and easily interpreted translucent andopaque bands. Readers agreement was 97% afterthe first counting and 100% after the second count-ing; four sagittae (0.5%) could not be read.

The first opaque zone appeared during the sec-ond spring, when fish were 19-21 months old,based on the September 1 birthdate. Marginal-in-crement analysis confirmed the recurring forma-tion of opaque zones during March-May. Duringthis time 90-100% of the otoliths for all age-class-es had opaque margins (Figure 2).

Monthly length-frequency distributions of reddrums shorter than 900 mm exhibited 2-3 modesthat represented ages 0, 1, or 2. The modes gen-erally corresponded to the lengths of fish with the

same otolith-determined ages (Figure 3). Conver-gence of modes after age 2 prevented discrimi-nation of older age-groups.

The annual periodicity of opaque zoneformation was confirmed by the recapture of reddrums injected with OTC. Otoliths from 4 of 118chemically marked fish were recovered. The OTCmark was on the margin of the sectioned sagittaefrom two fish at large less than 1 month. A thirdfish (1,090 mm) was released November 1989 andrecaptured August 1990; a fourth fish (1,295 mm)was released November 1989 and recaptured Oc-tober 1990. The OTC marks on both appeared onthe outer margin of a translucent zone beyondwhich were one opaque and one translucent zone.This zonation confirmed that one opaque zoneformed annually during the spring on red drumotoliths. These fish were 40 and 38 years old, re-spectively, when recaptured.

Red drums grew rapidly during their first 5years, after which annual growth was much slower;fish attained a maximum age of 56 years (Table 1;Figure 4). Variation within ages was considerable;1,000-1,100-mm fish were ages 8-52; 1,100-1,200-mm fish were ages 14-56, and 1,200-1,300-mm fish were ages 40-52. The world record reddrum (1,499-mm FL; 42.7 kg) was 53 years old,whereas the 55- and 56-year-old fish in this studywere 1,165 and 1,145 mm, and each weighed less

SEDAR 18-RD46

RED DRUM BIOLOGY 41

10nfln

Jan

50-

25-

120-

80-

40-

^

f

Feb

•IK,!. . . .Mar

*- 1 -—2 — 3

1 — **V -r

100

50-

0 ZOO e&o

200-

150-

100-

50-

g 300-•

1 200-

100-

30-

15-

30-

15-

•

-0-

1 J_,.

n. J1 .'

-r** —— , —— 410 200 4

Stp^

H— 3— •

I "̂

— Oct

i —— 2 — i

-•— • Nov

Dtc

: B __OO 600 800

Fork Length (mm) Fork Length (mm)

FIGURE 3.—Monthly length-frequency distributions of red drums sampled from North Carolina coastal waters,1979-1990. Horizontal lines represent the observed ranges of lengths for red drums of ages 0-3 each month forwhich fish were aged by otoliths. Ages were advanced I year on September I .

than 30 kg. Males ranged from 395 to 1,250 mmand from ages 0 to 56. Females ranged from 397to 1,346 mm and from ages 0 to 52.

Growth was best described by a continuous dou-ble von Bertalanffy curve (Vaughan and Helser

1990) for both sexes pooled. The regular von Ber-talanffy curve produced a distinct pattern of re-siduals—underpredicting for ages 2-6 and the old-est ages, and overpredicting for ages 9-23 (Figure4). Separate double von Bertalanffy growth curves

SEDAR 18-RD46

42 ROSS ET AL.

TABU- 1.—Predicted and mean observed fork lengths(FL. mm) for red drums sampled in North Carolina, 1987-1990. Sample si/.es (N) are in parentheses. Predictedlengths are from the continuous double von Bertalanffycurve.

PredictedAge FL

0 2791 4572 6393 7744 8755 8856 9037 9208 9369 951

10 9651 1 97812 9901314151617181920212223242526272829303132333435363738394041424344454647484950515253545556

.002,012.022.032,030.049.056.063.070,076,082,087.092.097,101.105.109.113.116.119.122,125.127.130.132.134,136,138.140.141.143,144.145.146.148.149.150.151.151.152.153.154.154.156

Observed FL

Mean (N)

312(35)421 (123)647(197)752(74)835(31)889(10)904(9)911 ( 1 3 )965(13)937(15)972 (24)986(14)967(35)987 (4)

1,023(17)1.022(42)1.014(40)1.020(56)1.004(19)1.017(10)1.087(2)1.070(1)1.030(1)1.086(2)1.104(4)1.170(1)

1.080(1)1 .122(2)1.090(2)1.121 ( 1 )1.160(1)

1 . 1 1 1 ( 1 )1.100(2)1.150(4)1.137(5)1.100(2)

1.139(3)1.218(2)1.086(1)

1.194(1)

1 .135(2)

1.140(4)

1.162(3)1,070(1)1.146(2)1.165(3)

1 ,165(1 )1.145(1)

Range

250-400271-718518-763641-855733-940859-933791-940870-978890-1,090895-991915-1.050917-1.050880- 1 .050965-1.003965-1.194959-1. 1 20928-1.168740-1.118752-1.085955-1.085

1,075-1. UK)

1.082-1.0901.065-1.150

1,110-1.1351.030-1.050

.070-1.130

.107-1.194

.065-1.193

.060-1.140

,115-1.183.090-1,346

1.130-1.140

1.110-1.181

1.090-1.250

1.137-1.1551.090-1.220

were generated for males (N = 329) and females(N = 340). The five parameters from each growthcurve were tested, based on their multivariale nor-mal distribution, by ini t ia l ly computing the Ho-telling's 72-statislic (2.20) and its correspondingF-statistic (0.44) (Morrison 1967; Bernard 1981).Because the computed F-statistic does not exceedthe tabled value at P = 0.05 (F - 2.21; df = 5and 663), there are no significant differencesamong the set of underlying parameters describinggrowth for the two sexes. The double von Berta-lanffy growth curve generated for sexes pooled(Figure 4; Table 1) melds two separate regular vonBertalanffy growth curves at tx (transition age) =4.4 years, with K\ = 0.30/year, K2 = 0.07/year, t\= -0.33 year, r> = -15.4 years, and Lx = 1,163mm.

The age composition of red drums sampled from1988 through 1990 included fish from age 0 to age56. with 29-34 age-groups represented annually(Figure 5). Age-0-3 red drums accounted for 51%of the combined samples, ages 4-10 for 14%, ages11-20 for 28%, and ages 20-56 for 6%. In additionto the expected peaks for age-0-3 fish, two othermodes were recurrent each season: ages 10 and13-17 in 1988; ages I I and 14-18 in 1989; andages 12 and 15-19 in 1990. Also recurrent weremodes representing ages 34-35 in 1988, ages 35-36 in 1989, and ages 36-37 in 1990. This annualprogression of age-groups probably reflects strongyear-classes and provides further validation of theannual formation of a single opaque zone.

The persistence of strong year-classes in theadult population was also apparent when age com-position data for 1968-1972 (W. Foster, North Car-olina State University, unpublished) and 1987-1990 were compared (Figure 6). Old red drums inrecent samples matched the prevalent 1936-1937,1940-1942, and 1951-1954 year-classes in the1968-1972 distribution. The strong year-classes of1932-1933 were represented by 55- and 56-year-old fish in recent samples.

The weight-length and fork length-total lengthregressions for red drums in North Carolina arepresented in Table 2. Because there was no sig-nificant difference between males and females forweight and fork length (F = 0.19; P > 0.66), thesexes were combined.

Maturity, Spawning Season, and SpawningGrounds

Unsexed, immature specimens were 250-627mm long and 0-1 years old. The overall sex ratio

SEDAR 18-RD46

RED DRUM BIOLOGY 43

1 ,«*UU -

1.200-

_ 1,000 -EE^ 800-B)§-J 600-^o"• 400-

i

200-

o-0

. _ M,._,^__^KjijE1^ "t T \ '

\ltiff MIvr- y 1'r/fl r ^, Comparison:

• Observed— ReguJar- - Double

1 1 1 1 1 I I 1 1 | 1 1 • 1 1 1 1 1 1 | M 1 t II i I 1 | 1 1 1 1 I I 1 1 1 | 1 |> 1 1 1 1 1 1 | 1 1 1 1 I I 1 1 q

l 10 20 30 40 50 6(

Age (years)

FIGURE 4.—Means (boxes) and ranges (vertical lines) of observed fork lengths (FL) of red drums from NorthCarolina coastal waters. 1987-1990. including comparison of predicted lengths from a regular (single) von Ber-talanffy growth curve (Lt = 1.114 mm FL. K = 0.19/year, fo = ~ 1.48) and a double von Bertalanffy growth curve(7-T = 1.163 mm FL. K\ = 0.30/year, K2 = 0.07/year. / j = -0.33 year, t2 = -15.4 years, tx = 4.4 years). Thesingle growth curve is derived from the formula L\ = L, \ I — e K^ '<^|. where L* = asymptotic length. K = growthcoefficient, and to is the hypothetical age at which fish length is zero. The double growth curve combines growthcurves for fish younger and older than a transitional age (/v), described by the formula: tx = (#2*2 ~ K\t\)l(K2 -K\), where K\ and t\ are for fish younger than the transitional age and K2 and 12 are for fish older than the transitionalage.

(349 males:373 females) was not significantly dif-ferent from 1 : 1 (x2 = 0.80: P > 0.99).

Female red drums in North Carolina waters ma-ture by age 4 (Table 3). No age-0-2 females ex-hibited vitellogenesis, but 57% of the age-3 and100% of the age-4 females were mature. Only 14%of the age-3 females had mature (well-developed)ovaries, but 43% were considered mature becausetheir ovaries contained postovulatory follicles orexhibited atretic activity during early fall. Thesmallest female with ovaries undergoing late-stagevitellogenesis was 773 mm, although a 733-mmfemale was classified spent. Maximum-likelihoodestimates (PROBIT analysis. Murphy and Taylor1989) of 20-mm increments indicated that 50%were mature at 801-820 mm. All females largerthan 860 mm were mature. Two old females (ages49 and 51) were senescent, with ovaries severelyatrophied and oogenic tissue absent; however fiveother old females (ages 40-52) caught betweenOctober and June were spent or resting.

Males matured at an earlier age and smaller sizethan females (Table 3). Earliest spermiogenesiswas observed in an age-1 (23-month-old) male.The youngest ripe male was age 2. More than 50%of the males were mature by age 2, and all weremature by age 3. Spermiogenesis was observed ina 520-mm male, and the smallest ripe male was700 mm. Fifty percent maturity for males wasreached at 621-640 mm (PROBIT), and all maleslarger than 740 mm were mature.

Peak spawning occurred in August and Septem-ber, based on maturity stages and gonadosomaticindices (GSI). Gonadogenesis began as early asMay in one male and one female, and was exhib-ited by 52% of the males and 77% of the femalesby July (Figure 7). Well-developed gonads wereobserved in females and males July through Sep-tember. Ripe males were found during Augustthrough early October, and two ripe females werecollected in August and September. Partially spentfish were collected during September and early

SEDAR 18-RD46

44 ROSS ET AL.

O O 10 10 20 30 90 «*0

1O 1O 2O OO 90 -4.0

Age (years)FIGURE 5.—Annual age composition of red drums sampled from North Carolina coastal waters, 1988-1990.

October. In all 3 years. GSI maxima for both sexesoccurred in August and September, with the ex-ception of August 1989, when only two small fe-males were collected (Figure 8).

Ripe and partially spent males, with well-de-veloped, ripe, and partially spent females werefound in estuarine and nearshore ocean waters.During August and September, ripe males andwell-developed females (N = 34) were caught at

the mouth of the Pamlico River, in bays betweenthe Pamlico and the Neuse rivers, and in PamlicoSound, 5-8 km inside of Hatteras and Ocracokeinlets over deep grass flats or channels. Catchesof adults from these waters declined during Oc-tober, but those remaining (N = 5) were all par-tially spent or spent. During that period, schoolsof large red drums found 5-10 km offshore ofHatteras Inlet and Ocracoke Island, and red drums

SEDAR 18-RD46

RED DRUM BIOLOGY 45

16 -

75 — '

50 -

25 -

.

1 987-1 99O

[Z]n-381

1 >r f

J7L ''0 *| ITI'I I ' l ' l ' l ITTI

1 93O 1 940 1 950 1 960 1 970

-i

/ /

/ /

// /

VI /r'Mi rri "T1 1 ' r n Tf I'l'i'i i i i i1 960 1 99O

Year-ClassFIGURE 6.—Frequency of cohorts represented in samples of adult red drums (5-56 years old) captured at Cape

Halteras. North Carolina, during 1968-1972 (Foster, unpublished) and in North Carolina coastal waters north ofCape Lookout during 1987-1990.

caught around the outer bars of Hatteras, Ocra-coke, and Drum inlets consisted of well-devel-oped, ripe, and partially spent males and females.By September, most (67%) of the adults caughtaround the inlets were spent. As the number ofadults found in estuarine waters declined in Oc-tober, they became more prevalent around the outerbars of each inlet, and virtually all were spent.

Fisheries and Size and Age Composition of theCatches

Commercial landings of red drums in North Car-olina increased from a mean of 37,681 kg/year

during the 1970s to a mean of 91,598 kg/year dur-ing the 1980s (Figure 9). Landings were dominatedby long-haul seine catches during the 1970s andby gill-net catches during the 1980s. Red drumsare a marketable bycatch of most inshore gears butare targeted during the fall with gill nets. Peaklandings occurred August through Novemberwhen the previous year's cohort attained legal size(357 mm FL) and recruited to most gears.

Annual recreational landings of red drums inNorth Carolina ranged from 40,735 to 146,514 kg(26,258 to 109.469 fish) during 1987 through 1990

SEDAR 18-RD46

46 ROSS ET AL.

TABLE 2.—Log weight-log length and fork length-total length regressions for red drum in North Carolina; Wweight (kg); FL = fork length (mm); TL = total length (mm).

Least squares equation

Log,0VV = -8.(X)8 4- 3.035log,()FLLog,0VV - 7.792 + 2.9351og,0FLFL - 25.933 f 0.9I4TLTL - -23.(X) + 1.087FL

A^

18297

586586

Range of lengths

250-1.346 mm280-1.270 mm

r2

0.990.990.990.99

(DMF, 1987 MRFSS survey, unpublished). Land-ings were low in 1990 following a severe freezein December 1989.

Red drums captured by both commercial andrecreational fisheries were typically small fish.From 1979 to 1990, 80% of the red drums sampledfrom commercial catches were 341-460 mm andwere caught during late summer or early fall when10-16 months old; only 4% were greater lhan 812mm. From 1987 ihrough 1990, 55-76% of ihe fishsampled from recrealional catches were less than460 mm; fish grealer lhan 812 mm made up only2-6% of ihe samples during 1987-1989, bul 16%during 1990.

TABLM 3.—Percent maturity of male and female reddrums in specified size-classes and age-classes. Fish cap-tured from September through December were included inthe previous age-class to maintain year-class integrityihrough a spawning season. Number of fish sampled (N)is in parentheses.

Percent maturity

Class Unknown sex

Fork length (mm)^400 0 (65)

4()1-5(X) 0(18)501-550 0(2)55 1 -600 0 ( 1 )601-650 0(4.)651-700701-75075I-8(X)HO 1-85085 1 -9(X)901-95095 1 - 1 .000> 1,000

Age (years)0 0(80)1 0(7)2 0 (1 )3456789

10>10

Males

0(2)20(10)21 (24)54 (28)52(31)86(22)

100(15)100(17)KM) (15)100(58)100(89)100(89)

0 ( 1 )31 (49)67 (70)

100(23)100(6)100(3)100(7)100(5)100(4)-100(15)100(3)100(135)

(N)

Females

0(3)0(12)0(12)0(29)0 (46)8(25)

10(20)54(13)93(14)

100(54)100(117)100(117)

0(3)0 (40)0(93)

57(21)100(10)KM) (4)100(5)100(8)100(5)100(12)100(9)100(125)

The year-class composition of adult (age-4-f)red drums sampled off Cape Hatteras from 1987through 1990 differed dramatically from samplestaken during 1968-1972 (Foster, unpublished; Fig-ure 6). Age-20 and older fish accounted for 67%of the adults in 1968-1972, but only 6.4% of theadults in 1987-1990. There were 46 year-classesrepresented in 1968-1972 (N = 191) and 40 year-classes in 1987-1990 (N = 381).

Tag-Recapture Data ami Mortality RatesThe short distance-of-movement patterns of red

drums justified treating North Carolina as a closedsystem for estimating survival rates from tag-re-capture data. Of the 1 ,1 13 subadull and adult reddrums tagged in North Carolina waters and recap-lured between 1984 and 1990, 99.7% were caughtin coastal or estuarine waters of North Carolina;one age-1 fish and two adults were caught in Vir-ginia waters (Ross and Stevens 1992).

Recapture rates for late age-0 and early age-1red drums in commercial and recreational fisherieswere very high. Tag return rates for the 1985-1989year-classes of red drums that were tagged when10-15 months old (July-December) ranged from18 to 25% by the end of the calendar year theywere tagged and from 21 to 28% through 1990(Table 4). After adjusting the data 50% to allowfor nonreporting (Pafford et al. 1990) and 20% forini t ial tag loss and tagging mortality (Gulherz etal. 1990), the recapture rates by cohort, as the co-horts in i t i a l ly recruited to the fisheries (August-December), ranged from 46 to 62% during the cal-endar year they were tagged (Table 4).

Total instantaneous mortality rates (Z) for sub-adull red drums were estimaled from bolh lag-recaplure dala and catch curve analysis. Estimatesof 5 for the 1985-1989 year-classes, based on theSeber (1970) and Robson and Youngs (1971) tagrecovery model, ranged from 6 to 24%; first-yearexploitation rates were 46-62% (Table 5). Thus,estimales of 2 ( = log,.,S) ranged from 1.44 to 2.74(Table 6). Year-class-specific estimates of Z fromcatch curves for North Carolina (Table 6) watersranged from 1.56 (1985) to 2.88 (1988).

SEDAR 18-RD46

RED DRUM BIOLOGY 47

12O

100 —

8O —

o>

If 60

40 -

20 -

O —'

Males (n=3O3)O Maturing

£3 Wall Davalopad

• Rip*

ffl Partially Spant

D Spant

sting

War Apr Jun Jul Aug

MonthSap Oct Nov Da>c

12O

100 —

80 —

0

t 6O —

40 -

20 -

Females <n = 226)n Maturing

Qwall Davalopad

• Rlpa

CD Partially Spant

C3 Spant

sting

Mar Apr May Jun Jul Aug

MonthSap Oct Nov Da>c

FiGi'RH 7.—Monthly frequency of occurrence of gonad developmental stages of mature red drums sampled inNorth Carolina waters during 1987-1990.

Because of the longevity of the red drum, naturalmortality can be expected to vary with age, in partbecause fish have fewer predators as they grow,and because adults and juveniles have differenthabitats (ASMFC 1990; Vetter 1988). We tried twomethods to generate more than one estimate of Mto reflect a nonconstant M. Natural mortality fromPauly's (1979) equation, with which we used the

double von Bertalanffy growth parameters Lt. K\.and Ki and an average annual water temperatureof 19°C (Williams et al. 1973) was 0.47 for ages0-5 and 0.18 for ages 6-56. These estimates, par-ticularly for ages 0-5, seemed biologically unrea-sonable for red drum, which has a 56-year life spanand few predators after age 1.

An alternative method, based on life history,

SEDAR 18-RD46

48 ROSS ET AL.

0.08-1

May

Month/YearFIGURE 8.—Monthly mean gonadosomatic indices (GSI) for red drums, exclusive of immature (stage-1) fish,

sampled in North Carolina from May 1988 through December 1990. Monthly sample sizes were 1-51 females and1-70 males. (Female sample sizes were less than 5 in July, August, October, and December 1988; June and August1989; and March. May, and October 1990. Male sample sizes were less than 5 in June and July 1988; June 1989;and March, April and July, and November 1990.)

1970 1990

FIGURE 9.—Annual commercial landings of red drum in North Carolina from 1970 through 1990 (source: NorthCarolina General Canvas Data from cooperative NMFS and DMF collection program) and recreational red drumlandings from 1979 to 1990 (source: Marine Recreational Finfish Statistics Survey).

SEDAR 18-RD46

RED DRUM BIOLOGY 49

TABLE 4.—Recapture rates of lagged 10-15-monlh-old red drums from 1985-1989 year-classes by commercial andrecreational fishing in North Carolina under two scenarios. Scenario 1: no adjustment for tag loss, tagging mortality,and nonreporting. Scenario 2: a 20% adjustment for initial tagging mortality and tag loss (Guther/ et al. 1990) and a50% adjustment for nonreporting (Pafford et al. 1990). Year-classes were tagged and released during the followingcalendar year.

• Recaptures by end of year released

Year-class(year released)and scenario

1985 (19X6)Scenario 1Scenario 2

1986(1987)Scenario 1Scenario 2

1987 (1988)Scenario 1Scenario 2

1988 (1989)Scenario 1Scenario 2

1989 (1990)Scenario 1Scenario 2

AllScenario 1Scenario 2

Numbertagged

1.459

427

733

270

36

2,925

Adjustednumbertagged

1,4591.167

427342

733586

270216

3629

2.9252,340

Numberreturned

329

79

142

55

9

614

Adjustednumber

recaptured

329658

79158

142284

55110

918

6141.228

Percentrecaptured

22.656.4

18.546.2

19.448.5

20.450.9

25.062.1

21.052.5

Overall

Numberreturned

410

100

171

58

9

748

recaptures through 1990

Adjustednumber

recaptured

410820

1002(X)

171342

58116

918

7481.486

Percentrecaptured

28.170.3

23.458.5

23.358.4

21.553.7

25.062.1

25.656.8

that provides age-specific estimates of naturalmortality from mean weight at age, was suggestedby Boudreau and Dickie (1989). This method, ap-plied to weakfish Cynoscion regal is (Seagraves1992) and red drums (Vaughan 1992), sets M =2.88 X VV"0-33. W being weight converted to kilo-calories. With mean weight at age for red drumestimated from age-length data, the following age-specific estimates of M were obtained: 0.41 at age0, 0.29 at age I, 0.18 at age 2, 0.15 at age 3, OJ3at age 4, 0.13 at age 5, and a mean of 0.11 forages 6-56 (range, 0.13-0.09). The mean of 0.22for ages 0-5 is a more reasonable estimate of Mthan 0.47 from Pauly's (1979) equation and wasthus used to estimate fishing mortality.

The instantaneous fishing mortality rates (F) forsubadult red drums were estimated by three meth-ods. The difference between Z (from both catchcurves and tag-recapture data) and M producedsimilar estimates of F for three of four year-classes(Table 6). Estimates of F from year-class-specificexploitation rates (M; Ricker 1975, equation 1 . 1 1 )generated by the tag-recapture model of Brownieet al. (1985) ranged from 1.06 to 1.49. These val-ues were lower than those estimated by the dif-ference between Z and M. Underestimating tagloss, tagging mortality, and tag nonreporting couldall result in underestimating F.

DiscussionAge and Growth

Sagittae are valid structures for determining theage of red drums in North Carolina. The formationof the first annulus during the second year andyearly annulus formation thereafter during the latewinter or early spring occurs in red drums sampledalong the U.S. southeast Atlantic coast (Pafford etal. 1990; Wenner et al. 1990) and in the Gulf ofMexico (Beckman et al. 1989; Murphy and Taylor1990). Direct validation of annuli in adults, basedon recaptured OTC-injected fish, was extended bythis research from 27-year-olds (Murphy and Tay-lor 1991) to at least 40-year-olds. The annual pro-gression of strong year-classes in 1987-1990North Carolina age composition data and the cor-respondence of old red drums captured during1987-1990 with strong year-classes hatched in the1930s and 1940s (Foster, unpublished) would oc-cur only if aging were valid and mortality rateswere equal across adult cohorts over time.

Red drums grow rapidly during their first 4-5years, after which growth slows as both sexes at-tain full maturity. This pattern of growth was re-ported in Florida (Murphy and Taylor 1990) andSouth Carolina (Wenner et al. 1990). The growthequations were not significantly different between

SEDAR 18-RD46

50 ROSS ET AL.

TABLE 5.—Bias-adjusted maximum-likelihood estimates of annual survival rales (S) and exploitation rates (M) basedon recapture matrix of red drums tagged when 10-15 months old, partitioned by year-class (1985-1989) and year ofrelease (1986-1990) in North Carolina waters. Number of fish tagged is adjusted for 20% tag loss and release mortality;number of recaptures is adjusted for 50% nonreporting of recaptured tags.

Yearclass

19851986198719881989

Yearreleased

19861987198819891990

Adjustednumberof fishlagged

1,16734258621629

Adjusted numbers of recaptured fish

1986 1987

658 154158

1988

436

284

1989

24

54I K )

in:

199()

2246

18

Survival rate

5

23.6913.8218.786.45

SF.

2.051.982.471.95

Exploitation rate

M

56.3846.2048.4650.9362.07

SE

1.452.702.063.409.01

the sexes, which confirms the findings of Vaughanand Helser (1990) for pooled south Atlantic reddrum data. No differences in growth rates werefound between sexes for 1-3-year-old red drumsin Florida (Murphy and Taylor 1990). althoughBeckman et al. (1989) generated growth modelsthat predicted larger females than males.

Growth was best described by a continuous dou-ble von Bertalanffy growth curve, which fits rapidearly growth with slower growth in later years andjoins them in a continuous curve at some transitionage (Vaughan and Helser 1990). This model wasbiologically reasonable because the transition ageseparated two distinct growth stanzas and corre-sponded with full maturity for both sexes as wellas the adoption of an adult migratory pattern (Rossand Stevens 1992).

Red drums attain their largest size and maximumlife span in waters between Cape Lookout and theVirginia barrier islands. The predicted Lx (1,163mm), the observed maximum lengths for males(1,250 mm) and females (1,346 mm), and theworld record (1,499 mm FL) exceed maximum

TABLE 6.—Summary of estimates of red drum mortalityrates in North Carolina, based on catch curve analysis andtag-recapture data.

Year-

Instantaneoustotal mortality

rate (Z) Inslan'

Tag-re- natural

curve data rate

Instantaneous fishingmortality rate (F)

Z2ub

class (Z,) Z, - M Z2 - M

1985198619871988

1.561.922.492.88

1.441.981.672.74

0.220.220.220.22

1.341.703.272.66

1.221.661.452.52

1.061.061.001.49

a Mean M for ages 0-5 are from age-specific estimates of M frommean weight at age (Boudreau and Dickie 1989; Vaughan 1992).

h A tag-recapture model (Ricker 1975, equation 5.3b) was used tocalculate M; A is the actual total mortality.

sizes reported from South Carolina to Texas (Table7). The oldest fish we sampled were 55 and 56years old, essentially the same as the maximumages (56 and 57 years) reported off North Carolinaduring 1968-1972 (Foster, unpublished). Blackdrums Pogonias cromis have been reported to liveat least 58 years (Murphy and Taylor 1989).

The existence of the oldest and largest red drumsin the higher latitudes of their range (North Car-olina and Virginia) is not unique. Conover (1990)noted that the maximum growth potential for fishmay vary inversely with the duration of the grow-ing season. The evolutionary basis for this phe-nomenon in subadults may be an adaptive responseto size-selective winter mortality in more temper-ate climates (Conover 1990). The attainment oflarger maximum sizes and greater longevity mayresult from increased metabolic costs for repro-duction in warmer southern waters (Edwards1984). Countergradient variation in growth ratewas noted for striped bass Morone saxatilus andAmerican shad Alosa sapidissima (Conover 1990),weakfish (Shepherd and Grimes 1983), and Atlan-tic croaker Micropogonias undulatus (While andChittenden 1977). The possibility that red drumsmove to more northern portions of their range dur-ing their lifetimes is unlikely. No fish tagged be-tween Florida and South Carolina have been re-captured as adults in North Carolina or Virginia,nor have red drums tagged south of Cape Lookoutbeen recaptured north of Cape Hatteras (Paffordet al. 1990; Wenner el al. 1990; Ross and Stevens1992).

Maturity, Spawning Seasonally, andSpawning Grounds

Male red drums mature at earlier ages and small-er sizes than females. In North Carolina, more than50% of ihe males were mature al age 2 and 100%were mature by age 3. This corresponds wilh red

SEDAR 18-RD46

RED DRUM BIOLOGY 51

TABLE 7.—Maximum reported ages and sizes of red drums (TL is total length: FL is fork length: M is male: F isfemale).

Slate (source) Age

Virginia (Claude Bain.Virginia Marine Re-sources Commission)

North Carolina (North 56Carolina Division of

Oldest fish

Length Sex Dale

None reported

1.145 mm FL M Ocl 1992

Weight (kg)

38.6

42.6

Largest fish

Length

1.397 mmTL

1.499 mm FL(53 years old)

Date

1981

Nov 1984

1.095 mmTLMarine Fisheries)

South Carolina (Charles 38Wenncr. Soulh CarolinaWildlife and Marine Re-sources Department)

Georgia (John Pafford. 40Georgia Department ofNatural Resources)

Florida (Michael Murphy. 35Florida Department ofNatural Resources)

Louisiana (Charles Wilson. 38 1.030 mm FLLouisiana Slate Univer-sity)

Te.\a«» (Robert Colura. 35Texas Parks and Wild-life Department)

Ocl 1986 34.0

1.057 mm FL M Nov 1989 21.5 1,066 mm FL

1,050 mm FL M Dec 1982 26.7

1990

1.055 mm TL M 1988

34.9

1965

1986

Aug 1983

Apr 1975

23.5 1.284 mmTL Nov 1967

drums in South Carolina, where most males ma-tured by the beginning of their third year (36months; Wenner et al. 1990), and Florida, whereall males were mature by age 3 (Murphy and Tay-lor 1990). In North Carolina, 50% of the femaleswere mature at age 3 and 100% were mature byage 4 (>860 mm FL). Similarly, off South Caro-l ina (Wenner et al. 1990) and in the northern Gulfof Mexico (Wilson et al. 1989), initial maturitywas reported at age 3, and most females were ma-ture during their fourth year. On the east and westcoasts of Florida, females mature at a smaller ini-tial si/e, but the length at 50% maturity (825-900mm FL) was similar to those from North Carolina(Murphy and Taylor 1990).

The peak spawning season for red drums inNorth Carolina waters is August and September.This was corroborated by recruitment of juveniles(10-30 mm) during September-October in state-wide estuarine trawl and seine surveys (Ross andStevens 1992). This confirms speculations of mid-August to October spawning off Chesapeake Bayand in the South Atlantic by Pearson (1929) andMansueti (1960) and is similar to the spawningseason off South Carolina (Wenner et al. 1990).Spawning occurs off both coasts of Florida duringSeptember and October (Murphy and Taylor 1990)but may begin in July (Peters and McMichael1987) and cease in early November (Johnson andFunicelli 1991). In the Gulf of Mexico, red drums

spawn from mid-August through mid-October offLouisiana (Wilson et al. 1991), but possibly as lateas February off Texas (Matlock 1984).

The presence of gravid and spent adults alongthe outer bars of inlets and in nearshore oceanwaters conforms with observations that red drumsfrom Chesapeake Bay to the east coast of Floridaspawn in coastal waters of the Atlantic (Mansueti1960; Tagatz and Dudley 1961; Yokel 1966). Reddrums in South Carolina and Georgia waters leavethe estuaries upon reaching maturity to spawn inthe sea (Music and Pafford 1984; Wenner et al.1990). In the Gulf of Mexico, spawning occursalong the beaches, often in the vicinity of passes,and in open waters along the Gulf side of the bar-rier islands from Florida to Texas (Yokel 1966:Matlock 1984; Murphy and Taylor 1990).

Red drums also spawn in the estuarine watersof North Carolina. Schools of adults occur fromAugust through early October over specific shoaland channel sites in Pamlico Sound near Hatterasand Ocracoke inlets, and around the mouths ofbays and rivers in western Pamlico Sound. Vir-tually all fish caught from these schools were inspawning condition. Spawning in estuarine watersis atypical for the species but not unique. A re-cently spawned female was caught 7 km inside themouth of Tampa Bay, Florida (Murphy and Taylor1990). Plankton tows, coupled with the presenceof spawning females far from inlets (Murphy and

SEDAR 18-RD46

52 ROSS KT AL.

Taylor 1990; Johnson and Funicelli 1991), indi-cated spawning in Mosquito Lagoon. Florida,where sonic tracking detected l i t t le directed move-ment of adults during the spawning season (Carrand Smith 1977). This conforms with our obser-vations that the schools of red drums in estuarinewaters of North Carolina remained in the samelocations for several weeks during August andSeptember.

Fishery and Mortality RatesRecapture rates of tagged subadults by the com-

mercial and recreational fisheries were extremelyhigh, indicating intense fishing pressure. Unad-justed annual (18-25%) and overall (21-28%) re-turn rates for juvenile red drums in North Carolinawaters were as high as rates from South Carolinato Texas, or higher. Over a 5-year period, 6-16%in South Carolina (Wenner et al. 1990) and 17-40% in Georgia (Pafford et al. 1990) were recap-tured by the end of the tagging year. In the Gulfof Mexico, annual tag return rates were 1 1-25%in Florida (Murphy and Taylor 1990) and 8-13%for subadult red drums in Texas lagoons (Green etal. 1985).

Unadjusted recapture rates for red drum werehigher than for all other species tagged in NorthCarolina's coastal waters. Return rates for summerflounder Paralichthys dentatus and southern floun-der P. lethostigma were 6% overall and 3-13%annual ly during a 5-year study (R. Monaghan,DMF, personal communication). Both species weresubjected to intensive recreational or commercialfishing pressure, or both, and summer flounderwere assessed to be overfished (MAFMC 1990).Tagged Atlantic croakers, which were commer-cially harvested throughout the year and exhibitedsigns of growth overfishing, were returned at anoverall rate of 3% (1-9% annually; D. DeVries,NMFS, personal communication). Only tag returnrates for striped bass were as high as those for reddrum. Slocked and tagged juvenile striped basswere returned at an annual rate of 7-29% from1981 through 1987 and reflected a severely over-fished population during the early and mid-1980s(S. Winslow. DMF, personal communication).

Very high estimates of total mortality indicatedlow survival of female red drums to maturity. Totalmortality from both catch curve and tag-recapturedata for the 1985-1988 year-classes translates toonly 6-24% annual survival . The strong year-classes of 1982 and 1985 were followed by highcommercial landings in 1983-1984 and 1986-1987. Thus, the contribution of recent year-classes

to the adult population, compared with the 1971-1973 and 1978 year-classes, was low.

Annual survival rates of subadults in North Car-olina were as low or lower than reported in theU.S. south Atlantic or Gulf of Mexico. Survivalrates from cohort-based catch curves in South Car-olina and Georgia were 6-29% and 15-43%, re-spectively (Vaughan and Helser 1990). In Floridawaters, survival rates were 2-13% for 2-4-year-olds in the Gulf of Mexico and 24-50% for 2-6-year-olds in Mosquito Lagoon (Murphy and Taylor1990). Subadult annual survival rates were 12-20% in Texas lagoons, based on tag-recapture data(Green et al. 1983). The populations were consid-ered overexploited in all cases, and strict man-agement measures were recommended. Survivalrates in North Carolina waters were similar to theoverall rates estimated for the south Atlantic (16-19%; Vaughan and Helser 1990).

Continued excessive fishing pressure on sub-adult red drums in North Carolina could ultimatelyreduce the spawning stock below levels sufficientto maintain the population. Vaughan and Helser(1990) estimated that the spawning stock ratio for1986-1988 ranged from 2 to 3%, well below theSouth Atlantic Fishery Management Council'sgoal of 30% (SAFMC 1990).

Acknowledgments

We appreciate the time, effort, and patience ofthe following commercial fishermen who assistedus with the capture of red drums: M. Langowski,E. Dickens, R. Morgan, L. Paul, G. Paul, and D.Ormond. We are indebted to several Outer Bankstackle shops, commercial fish packinghouses, andCaptain N. Miller for collecting red drum carcassesfor assessments of age, growth, and reproductivebiology. C. Wenner and W. Roumillat (South Car-olina Marine Resources Research Institute) gra-ciously provided their time and facilities in makinghistological preparations of our gonad samples. Weappreciate the contributions of DMF staff, includ-ing J. Zuaboni, M. Millard, B. Burns, L. Judy, andothers for field work and sample and data collec-tion; L. Mercer. M. Street, R. Monaghan, and S.Winslow for constructive comments on the manu-script; D. Willis for typing and organizing the finalmanuscript; and P. Phalen, M. Tangedal, and D.Tootle for computer data processing. This projectwas conducted under the Federal Aid in Sport FishRestoration Act and funded, in part, by the U.S.Fish and Wildlife Service, under project F-43.

SEDAR 18-RD46

RED DRUM BIOLOGY 53

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Received June I I . 1993Accepted July 22. 1994

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