Population dynamics of spot - Springer Link

Estuaries

Vol. 7, No. 4A, p. 444-450

December 1984

Population Dynamics of Spot, Leiostomus xanthurus, in Polyhaline Tidal Creeks of the York River Estuary, Virginia I MICHAEL P. WEINSTEIN 2

Virginia Institute of Marine Science Gloucester Point, Virginia 23062 LARRY SCOTT STEVEN P . O ' N E I L 3

Department of Biology Virginia Commonwealth University Richmond, Virginia 23284 ROBERT C. SIEGFRIED II STEPHEN T. SZEDLMAYER

Virginia Institute of Marine Science Gloucester Point, Virginia 23062 ABSTRACT: Most populations of estuarine-dependent, early life stages of marine fishes are open. As a result, it has been difficult to apply conventional population models to most systems. In this study, a marked population of young-of-year spot (Leiostomus xanthurus) was released into a polyhaline tidal creek within the Guinea Marshes of the York River estuary, Virginia. Over a 90day study period, 221 marked fishes were recaptured. Plots of the ratio of marked to unmarked individuals (mi/ni) in subsequent samples indicated that the population was resident in the creek for up to 162 days with the average individual present for 81 days. When this population turnover rate was compared to the total population decay rate (marked plus unmarked fish), it was determined that exchange between habitats (immigration/emigration) accounted for about 36.4% of the total decay rate, with the remainder attributed to natural mortality. By correcting the overall disappearance rate for population turnover due to emigration and using this adjusted value as a measure of instantaneous mortality (z), the estimated production (over 90 days) in this population was 23,630 cal (98,870 J) per m 2. This figure agrees with a previously derived estimate for spot in the Guinea marshes and is nearly two orders of magnitude higher than other reported values for this species for all size classes over the entire growing season.

tion turnover associated with movement between habitats (immigration and/or emigration). Failure to account for such movements may result in considerable underestimates of production (Weinstein 1983). This is because z, the instantaneous mortality rate in the population, is usually estimated from the descending limb of the population abundance curve which includes an unknown measure of population turnover (Pearcy 1962; Adams 1976, Chapman 1965; Weinstein and Waiters 1981). Population models derived from mark-

Introduction Most populations of immature estuarinedependent species are open; i.e., once recruitment to the primary nurseries ceases, there remains a certain amount of populaContribution No. 1202, Virginia Institute of Mafine Science, Gloucester Point, Virginia. 2 Present address: Lawler, Matusky and Skelly, Engineers, One Blue Hill Plaza, Pearl River, New York 10965. 3 Present address: Virginia Institute of Marine Science, G~oucestcr Point, Virginia 23062. 9 1984 Estuarine Research Federation

444

0160-8347/84/04A0444-07$01.50/0

Spot, PopulationDynamics,Marshes

recapture data also include assumptions of negligible immigration/emigration rates (Seber 1973). Even the classical Jolly-Seber method (Jolly 1982) for open populations requires that emigration be permanent, an assumption which may be easily violated in marine systems. The few models which can account for population turnover (Seber 1962; Paulik 1963; Parker 1963) require multiple-marking and recapture events and are either labor intensive or not generally amenable to studies of fragile young-of-year. Weinstein (1983) developed a simple method to account for population turnover due to emigration. The technique stems from the work of Parker (1955) who estimated recruitment of new individuals into a marked population. By modifying his method to account for events occurring after recruitment, Weinstein (1983) was able to establish a "dilution" factor for marked spot (Leiostomus xanthurus) residing in a small (4 ha) tidal creek. It was assumed that the dilution rate was associated with marked animals leaving the population and being replaced by unmarked individuals. This approach led to an estimate of population turnover rate of about 26% of the total decay rate. In addition, it was estimated that an average individual remained in the creek for 91 days, a much greater degree of residency than was anticipated for this small system. In the present study, we extend these methods to a creek of much larger size, but within the same general area of the Guinea Marshes, York River estuary, Virginia. As in the earlier effort, young-of-year spot were marked and released within the confines of the tidal creek. Our specific objectives were to (a) determine residence time and extent of movement between the creek and adjacent areas; (b) measure turnover rate of spot in the creek; (c) estimate the mean growth rate of spot in the creek, and (e) during their residency period, estimate spot production in the creek. Study Area Blevins Creek (Fig. 1) is the largest tidal drainage system located in the Guinea Marshes of the York River estuary. A dredged channel, with a depth of about 4 m, is maintained immediately outside of the

445

.~11r ~ ~ #BLEVINSCR. ~, ,~.~ ~ ~ - - - ~ ~ ?

J

J-

~

MARSHES , ~ . v - ~ j " a . . ~ l

tl

Fig. 1. Study area at Blevins Creek, Guinea Marshes, York River, Virginia. A parallel study was conducted in 1982 at Little Monday Creek.

creek mouth to accommodate commercial traffic entering Brown's Bay. The creek shoreline is bordered by Spartina alterniflora meadows with intermittent patches of Juncus sp. Tidal amplitude within the creek averages 1.6 m with all major tributaries remaining inundated at low water. Shallow subtidal areas outside of the creek mouth (adjacent to the channel) are carpeted by patchy stands of Zostera marina and Ruppia maritima. Salinities in the Guinea Marshes are usually in the polyhaline range. Materials and Methods Details of the experimental design and methods are presented elsewhere (Weinstein 1983). Briefly, large numbers of individuals were marked by "sandblasting" with fluorescent pigments at a spray pressure of 6.5 kg per cm 2 (Tohiyat 1979; Dolloffand Huish 1980). Fish were captured with either a 30.5 m haul seine (6.5 mm mesh) in upper shallow tributaries or with a 6.2 m semiballoon otter trawl (wings and body of 19 m m mesh and a liner of 1.0 mm mesh) in the lower creek mainstem, held temporarily in live boxes, and then released in the area of capture immediately after being marked. On June 6-9, 8,260 fish marked with red pigment were released in the upper tributaries of Blevins Creek; on June 9 and 10, 2,137 fish marked with green pigment were released in the lower mainstem portion of the creek. The combined release totaled 10,397 individuals. To estimate the rate of mortality of marked fish, groups of randomly selected batches of spot were held in the laboratory

446 TABLE

M. P. W~nsta~n at al. 1.

Survival rates o f marked spot

(Leiostomus xanthurus), held for 96 h in 600 I tanks o f running

seawater. N u m b e r Alive at End of:

Seined fish Trawled fish

Survival Rate

0 h

24 h

48 h

72 h

96 h

n

%

170 108

155 88

122 63

111 63

105 63

105 63

61.6 58.3

for 96 h in 600 l circular tanks filled with running seawater. Fish were divided according to m e t h o d o f capture and transferred to the holding tanks. At subsequent 24 h intervals dead fish were r e m o v e d from the tanks, measured for standard length and examined for pigment. Survivors at the end o f 96 h were treated similarly. At the end o f 96 h, 61.6% (Table 1) o f the seined fish (Weinstein 1983) and 58.3% o f the trawled fish remained alive. In addition, all fish from the holding experiments were well marked. Previously, T o h i y a t (1979) demonstrated that 97% o f Atlantic croaker (Micropogonias undulatus) 60-90 m m SL retained pigment for at least 8 months, while Dolloff and Huish (1980) using a spray pressure o f 7.03 kg per cm 2 on young-of-year bluegill (Lepomis macrochirus) found that 96% o f all mortality occurred within the first 6 days o f a 53-day holding experiment. Thus, our conclusion that 6,334 marked fish would survive for the duration o f our experiment and that all marked fish would retain their pigment appeared to be correct. S a m p l i n g to r e c a p t u r e m a r k e d fishes c o m m e n c e d on June 13. The creek was sampled on 12 subsequent dates through September 8. Until June 24 it was sampled about every 4 days; thereafter, intervals were about once a week (until July 29) and twice a m o n t h (after July 29). The adjacent dredged channel was sampled during the interval June 13 to August 15 on the same schedule as the creek. Depending on tidal stage, samples were collected in the creek by either bag seine or trawl. T o standardize these gears for catch-per-unit-effort (CPUE), the following correction factors were used. The trawl swept an area o f 627 m 2 (Weinstein and Brooks 1983), while the area encompassed by the haul seine sweep was 470 m 2. The latter was determined by extending the net from shore in an arc and measuring the distance to the arc apex and the distance between contact points on the shore line

(this was the standard m e t h o d by which the haul seine was deployed from a small j o n boat). Gear efficiency for the 6.1 m trawl was determined from the study o f Kjelson and Johnson (1978) where their c o m b i n e d efficiency for all experiments on juvenile spot during daytime was 32.3%. An efficiency value o f 40.6% determined for juvenile white perch (Morone americana) and striped bass (M. saxatilis) was used for the haul seine (Texas Instruments 1978). It was assumed that similar sized spot would be equally susceptible to this gear (see also Weinstein and Davis 1980). Because pigments on recaptured fishes were not visible under field conditions, it was necessary to return all fish to the laboratory for examination under long wavelength ultraviolet illumination. Marked individuals also were routinely measured for standard length. Total decay rate (mortality + emigration) in the tidal creek spot population was expressed by regressing log~0CPUE on sampling date. The regression o f log~o m a r k e d / u n m a r k e d (mi/ni) individuals on sampling date was used to indicate population turnover in the creek. Secondary production (P) was calculated by a computer version o f the basic production model (Ricker 1946; Allen 1950), as modified by Adams (1976): P = G])

(1)

G = log~2 - log~l/At

(2)

= B0(eC-z - 1)/G - Z

(3)

where

Z = - (log, N2 - log, N 0 / A t

(4)

G is the instantaneous growth rate; 1) is the mean standing stock biomass in a given time interval; Z is the instantaneous mortality rate. x~ and ~2 are the mean weights o f individuals at each station at time t, and tz, respectively, and N, and N2 are the n u m b e r

Spot, Population Dynamics, Marshes TABLE 2. Recapture data for spot (Leiostomus xanthurus) in Blevins Creek. T(c.,,,) = cumulative number of days between samples, n i = number of individuals in the ith sample, mi = number of marked fish in ith sample. CPUE = catch-per-unit-effort.

447

o

-1.61

GO 9

o

- 1.7

~.

o

o

-0.2 -OA

l~te

Jun. 13 17 20 24 Jul. 1 8 15 22 29 Aug. 15 26 Sept. 8 Totals

T(~)

0 4 7 11 18 25 31 38 45 66 77 90

n~

m,

1,071 1,703 1,850 1,859 661 860 983 950 643 444 562 282 11,868

20 38 26 52 11 11 21 19 10 4 5 3 220

Ratio (m/n0

0.019 0.022 0.014 0.028 0.017 0.013 0.021 0.020 0.016 0.012 0.009 0.011

CPUE ( n / m =)

0.561 0.619 0.617 0.727 0.495 0.488 0.317 0.259 0.206 0.150 0.107 0.058

o f individuals per m 2 present at t~ and t2, respectively. T o estimate biomass, standard length (SL) was converted to dry weight using the relationship: log~o(W)= 3.2726 logl0SL 5.8751 (r 2 = 0.999; Brooks et al., unpublished results). A conversion value o f 5.139 Kcal (21,532 J) per g (dry weight) for spot was used (Thayer et al. 1973). The instantaneous mortality rate, Z, was adjusted to reflect the difference between the slopes o f the C P U E and m~/ni curves; i.e., the partitioning o f the total decay rate into mortality and population turnover rate. C P U E was also adjusted to reflect gear efficiency. Results Returns o f marked fish indicated that most spot remained in Blevins Creek and virtually none were detected in the adjacent dredged channel. Only a single individual in the total sample collected in the channel was marked (1/1,486 = 0.07%); whereas, 220 o f the 11,868 fish captured in the creek (1.9%) were pigmented. Because o f the low return rate o f m a r k e d fish, the channel was not sampled after August 15. By the third sampling date, June 20, both red and green marked fish were showing signs o f r a n d o m mixing throughout the creek, but it was not until July 8, approximately 3 weeks after they were released that returns based on pigment color (adjusted for relative propor-

;

~ 1.9

B -2.0

-G8

ml/l~ I

y=-O.

4x-t07

O

- 2.1

- t.O 9

10

r2 =CtO~

20

30

- 1.2

40

50

80

70

80

90

tlIDAYSI

Fig. 2. Results of marking study at Blevins Creek. Log~o of catch-per-unit-effort (Iog~oCPUE) is plotted against the cumulative number of days (tO between samples. Similarly, logto of the ratio of marked to unmarked fish (logtom/n~ in each sample is plotted against t~. Closed circles, CPUE; open circles, mi/n~.

tions) were completely r a n d o m from different sections o f the creek. Total decay rate o f the marked population (mortality + emigration), along with the ratio o f marked to u n m a r k e d fish in each sample (mi/ni) is shown in Table 2 and Fig. 2. The slope o f the equation o f the log~o C P U E line, y = - 0 . 0 1 lx - 0.13, was significantly different from zero (p < 0.01; r 2 = 0.958) as was the slope o f the regression o f loglomi/ni on sampling date, y = - 0 . 0 0 4 x 1.67 (p < 0.01, r 2 = 0.529). Moreover, comparisons o f the slopes o f loglo C P U E and log~o(mi/ni) regressions indicated that they differed significantly, t = 6.47, p < 0.01. I f the dilution rate o f the marked population is extrapolated through time, it is estimated that the population turnover rate was about 162 days, with an average individual remaining in Blevins Creek for 81 days. These values were determined from mi/ni on day zero and day 90, and the arithmetic decay rate o f the line joining these points. Biomass production o f spot between June 17 and September 8 was estimated at 4.598 g per m 2, or 23,630 cal (98,870 J) per m 2. In calculating these values, it was assumed that population turnover rate was about 36.4% o f the total decay rate (Fig. 2) and that growth was reflected in increases in mean length o f marked fish in each sample (Table 3). The latter is probably an over estimate because mortality due to predation

448

M.P. Weinsteinet al.

TABLE3. Estimatedgrowthrates for spot (Leiostomusxanthurus)based on recaptures of marked fish. n = number of individuals. AL = change in length. At = time interval. G = growth.

Holding experiments (June 7-11) Jun. 13 17 20 24 Jul. 1 8 15 22 29 Aug. 15 26 Sept. 8

Mean Length (mm)

n

AL

At

44.0 45.3 44.6 49.9 50.9 53.5 62.0 69.7 74.7 75.4 86.5 94.6 97.3

65 20 38 26 52 11 11 21 19 10 4 5 3

1.3 -0.7 4.6 1.0 2.6 8.5 7.7 5.0 0.7 11.1 8.1 2.7

4 4 7 4 7 7 7 7 7 17 11 13

G(AL/At)

0.33 -0.669 0.25 0.37 1.21 1.10 0.71 0.10 0.65 0.74 0.21

9Growth estimate derived from change in length between June 13 and June 20. is likely size-dependent; however, it is offset somewhat by the observation that the largest individuals in the population are more likely to emigrate (Weinstein and Brooks 1983). Discussion

Previous marking studies ofestuarine-dependent species were generally restricted to estimates o f residence time and establishment o f migratory patterns (Arnoldi et al. 1974; Yakupzack et al. 1977). Although generally successful, these efforts were limited by the scale o f the system and by lack o f an experimental design specific for estimating population parameters. W h e n we began two years ago, we were uncertain just how open our population was. Weinstein (1983) described several potential scenarios which might be faced in c o m i n g to grips with this problem. In the worst case, the population might turn over so rapidly as to render our efforts futile. At the opposite extreme, it was hoped that the spot population would be sufficiently resident as to allow

recapture o f marked individuals over an extended period, thus allowing us to address the objectives stated in the I n t r o d u c t i o n (see also Weinstein 1983). At the outset, we attempted to mark a large sample so as to delay, as along as possible, complete dilution o f the m a r k e d population. O u r original goal was to m a r k 10% o f the spot present in each creek; it soon became clear that there were extraordinarily high densities in these areas and that this was an overly optimistic goal. As m a y be seen in Table 2, the surviving m a r k e d fish over the first week o f the study (June 13-24) constituted only 1.4% to 2.8% o f the total spot catch. I f the mean o f these values is taken along with our estimates o f surviving fish and the n u m b e r o f unmarked fish in each sample, the estimated n u m b e r o f spot in Blevins Creek is approximately 302,000 individuals (based on the Peterson Index, Ricker 1975). This figure actually translates into considerably lower unit area densities than reported for Little M o n d a y Creek in the previous year (Weinstein 1983). Rather than being a creek

TABLE 4. Comparison of results of marking studies on spot (Leiostomus xanthurus) in the Guinea Marshes, York River Estuary, 1982-83.

Residence period Population decay rate (per day) Turnover rate (per day) Turnover rate as a % of total decay rate Production cal (J) per m 2

Little Monday Creek 1982

Blevins Creek 1983

182 (mean = 91) 0.023 0.006 26.1 21,550 (90,167)

162 (mean = 81) 0.011 0.004 36.4 23,630 (98,870)

Spot, Population Dynamics, Marshes

associated difference, it is likely that spot recruitment to the Chesapeake Bay was lower in 1983 compared to 1982. When the results of the two year effort are compared, it is clear that spot population dynamics are similar in both creeks (Table 4). It is intriguing that mortality rates were lower in 1983 corresponding to lower population densities. Growth rates also were higher in 1983, we wonder whether or not we are observing density-dependent phenomena; however, these observations are obviously complicated by potential creek differences, higher mean temperatures in the shallows in 1983 and the simple lack of sufficient data. It is interesting to speculate on how these trends might compare if carried out over several additional years. Because few spot ventured into the adjacent dredge channel nor were captured in local grassbeds (Weinstein 1983), it seems reasonable to conclude that the exchange process is localized among creeks. This conclusion is strengthened somewhat by additional observations. Smith et al. (1984) and O'Neil (1983) demonstrated that shortly after recruitment, greater numbers of youngof-year spot were captured in tidal creeks than on immediately adjacent shoal areas, a trend which continued until the fall migration. Similarly, Weinstein and Brooks (1983) reported nearly four times greater densities of spot from tidal creeks on the eastern shore of Virginia compared to adjacent seagrass meadows. Spot also were larger in the creek earlier in the year (April and May), but, thereafter, were smaller which suggests that it is the larger individuals in the population that are likely to emigrate. Collectively, all of our observations (and those of others) support the idea that each marsh system harbors a seasonally resident population of Leiostomus xanthurus and that population turnover rates in individual creeks are relatively low. If further studies confirm this hypothesis, we would have the opportunity to evaluate the primary nurseries on an individual basis. We are presently undertaking this effort with studies of daily growth rates of spot based on otolith increments and ~4C glycine uptake in scales of individuals > 40 mm standard length.

449

Adams (1976) reported seasonal production for all age groups of spot in seagrass meadows at Bogue Sound and Phillips Island, North Carolina as 37 (155 J) and 356 (1,492 J) cal per m 2, respectively. As suggested above, however, if spot are transient in grassbeds rather than residents, these estimates may actually reflect energy transfers which are primarily occurring elsewhere . In any case, our estimates for the 90-day periods in Little Monday Creek, 21,550 cal (90,167 J) per m 2 and Blevins Creek, 23,630 cal (98,870 J) per m 2 are approximately two orders of magnitude higher. Part of this difference is due to adjusting for gear efficiency but a substantial portion of it is also a result of accounting for emigration. Unfortunately, attempts to refine these estimates further, for example, by accounting for the role of immigrants from nearby creeks would be too labor intensive. It is also impractical to mark sufficient numbers of spot in the seagrass meadows to determine events taking place there. Average residency of spot in tidal creeks of the Guinea Marshes was about 86 days (Table 4). This degree of residency, exhibited by a species recruited into the Chesapeake Bay in a more or less random fashion (from spawn originating offshore), indicates that subsequent active habitat selection is taking place (Weinstein 1983). However, establishing patterns of distribution of estuarine species based on "choice" has yet to be distinguished from passive determinants such as differential mortality (Polgar 1982). The approach developed in our studies should prove valuable for measuring similar aspects of population dynamics in other estuarine species. One obvious direction for future research would involve the adaptive values associated with habitat choice. Because of commonalities in general life history patterns, it is also possible that spot share these traits with other estuarine-dependent species. ACKNOWLEDGMENTS We thank A. Earles and K. Anderson for help in the field and laboratory. G. Dunaway typed several versions of the manuscript. This project was supported by EPA grants R808707 and R810334 to MPW and by the Virginia Institute of Marine Science.

450

M.P. Weinstein et al.

LITERATURE CITED ADAMS, S.M. 1976. The ecology ofeelgrass, Zostera marina (L.) fish communities. II. Functional analysis. J. Exp. Mar. Biol. Eco. 22:291-311. ALLEN, K. R. 1950. The computation of production in fish populations. N.Z. Sci. Rev. 8:89. ARNOEDI, O. C., W. H. HERKE, AND E. J. CLAIRAIN, JR. 1976. Estimate of growth rate and length of stay in a marsh nursery of juvenile Atlantic croaker Micropogon undulatus (Linnaeus), "sandblasted" with fluorescent pigments. Gulf Caribb. Fish. Inst. Proc. 26th Ann. Sess., p. 158-172. CHAPMAN,D. B. 1965. The estimation of mortality and recruitment from a single tagging experiment. Biometrics 21:529-542. DOLLOFF, C. A., AND M. T. HUISH. 1980. Immersion staining and fluorescent pigment spraying o f juvenile fish: An analysis of some factors influencing the success of these marking techniques. Report 80-1, Cape Fear Studies, Carolina Power and Light Co., Raleigh, NC. 66 p. KJELSON, M. A., AND G. N. JOHNSON. 1978. Catch efficiences of a 6. l m otter trawl for estuarine fish populations. Trans. Am. Fish. Soc. 107:246-254. JOLLY, G . M . 1982. Mark-recapture models with parameters constant in time. Biometrics 38:301-321. O'NEIL S.P. 1983. The distribution and trophic ecology of young-of-year spot (Leiostomus xanthurus, Lacepede) in polyhaline verses meso-oligohaline tidal creeks and adjacent shoals of the York River, Virginia. M.S. Thesis, Virginia C o m m o n w e a l t h Univ., Richmond, 55 p. PARKER, R. A. 1955. A method for removing the effect of recruitment on Peterson-type population estimates. J. Fish. Res. Board. Can. 12:447-450. PARKER, R.A. 1963. On the estimation of population size, mortality and recruitment. Biometrics 19:318323. PAULIK, G.J. 1963. Estimates of mortality rates from tag recoveries. Biometrics 19:28-57. PEARCY, W . G . 1962. Ecology of an estuarine population of winter flounder, Pseudopleuronectes americanus (Walbaum). II. Distribution and dynamics of larvae. Bull. Bingham Oceanogr. Collect. 18: 16-38. POLGAR, T.T. 1982. Larval retention: Transport behavior, or differential mortality? Estuaries 4:276277 (abst.). RICKER, W. E. 1946. Production and utilization of fish populations. Ecol. Monogr. 16:374-391.

RICKER, W.E. 1975. Computation and interpretation of biological statistics offish populations. Bull. Fish. Res. Board Can. 191. SEBER, G. A. G. 1962. The multi-sample single recapture census. Biometrika 49:339-350. SEBER, G. A . G . 1973. The Estimation of Animal Abundance. Griffin, London. 506 p. SMITH, S. M., J. G. HOFF, S. P. O'NEIL, AND M. P. WEINSTEIN. 1984. Community and trophic organization of nekton utilizing shallow marsh habitats, York River estuary, Virginia. Fish. Bull., U.S. 82. TEXAS INSTRUMENTS. 1978. Catch efficiency of 100 ft (30 m) beach seines for estimating density of youngof-year striped bass and white perch in the shore zone of the Hudson River estuary. Final Report to Consolidated Edison Company, NY. 81 p. THAYER, G. W., W. E. SCHAAF,J. W. ANGELOVIC,AND M. W. LACROIX. 1973. Caloric measurements of some estuarine organisms. Fish. Bull., U.S. 7 1 : 2 8 9 296. TOHIYAT, M . D . 1979. Retention of fluorescent pigment marks by juvenile Atlantic croaker, Micropogon undulatus (Linnaeus). M.S. Thesis, Louisiana State University, Baton Rouge. 68 p. WEINSTEIN,M . P . 1983. Population dynamics of an estuarine dependent fish, the spot (Leiostomus xanthurus), along a tidal creek-seagrass meadow coenocline. Can. J. Fish. Aquat. Sci. 40:1633-1638. WEINSTEIN, M. P., AND H. A. BROOKS. 1983. Comparative ecology of nekton residing in a tidal creek and adjacent seagrass meadow: Community composition and structure. Mar. Ecol. Prog. Ser. 12:1527. WEINSTEIN,M. P., AND R. W. DAVIS. 1980. A comparison of the collection efficiency of seine and rotenone sampling. Estuaries 3:98-105. WEINSTErN, M. P., AND M. F. WALTERS. 1981. Growth, survival and production in young-of-the-year populations of Leiostomus xanthurus Lacepede, residing in tidal creeks. Estuaries 4:185-197. YAKUPZACK, P. M., W. H. HERKE, AND W. G. PERRY. 1977. Emigration of juvenile Atlantic croakers, Micropogon undulatus, from a semi-impounded marsh in southwestern Louisiana. Trans. Am. Fish. Soc. 106:538-544.

Received for consideration, October 22, 1983 Accepted for publication, January I0, 1984