M. Ted Tyndall. SEASONAL AND DIEL FEEDING PATTERNS AMONG JUVENILE FISH
IN BOND CREEK, BEAUFORT COUNTY, NORTH CAROLINA. (Under the direction of
Charles W. O'Rear, Ph.D.) Department of Biology, July 1987.
The seasonal and diel feeding pattern of spot (Leiostomus
xantkuvus), Atlantic croaker (Micvoyogonias undulatus), southern
flounder (Pavatidhthys lethostigma), and bay anchovy (Andhoa mitdhi.lt'í)
were examined during their residence in the irridreaches of Bond Creek.
Stomach analysis in addition to estimates of the abundance of zooplank-
ton and benthos indicated that spot and Atlantic croaker are opportun-
istic feeders. The items most often found in the stomachs were usually
those items exhibiting a seasonal peak in abundance. Southern flounder
however, extensively utilized mysids regardless of the season and exhib-
i ted a secondary piscivorous feeding habit. Bay anchovy were found to
be zoopl ankti vores utilizing larger zooplankton with increasing size.
Little diel difference was seen in the type of prey consumed.
Benthos however, were consumed more frequently at night by spot in early
spring and late summer and in early summer by Atlantic croaker.
Diet breadths were widest in spot and Atlantic croaker and narrow-
est in southern flounder and bay anchovy. Diet overlap values were high
for all six combinations. Mysids were the most selected prey using
Ivlev's electivity index while calanoid copepods were the most avoided
prey. Food source was not limited in Bond Creek during the study period
consequently the four species occupied similar niches within Bond Creek.
SEASONAL AND DIEL FEEDING PATTERNS
AMONG JUVENILE FISH IN BOND CREEK,
BEAUFORT COUNTY, NORTH CAROLINA
A Thesi s
Presented to
The Faculty of the Department of Biology
East Carolina University
In Partial Fulfillment
of the Requirements for the Degree
Master of Science in Biology
by
M. Ted Tyndall
July 1987
SEASONAL AND DIEL FEEDING PATTERNS
AMONG JUVENILE FISH IN BOND CREEK
BEAUFORT COUNTY, NORTH CAROLINA
by
M. Ted Tyndall
APPROVED BY:
DIRECTOR OF THESIS
COMMITTEE MEMBER
Mark M. Brinson, Ph.D.
'
COMMITTEE MEMBER // ? ÙeiU,
Vincent •I/ Beilis, Jr.^P)h?.D.
COMMITTEE MEMBER
Ronald G. Hodson, Ph.D,
DEAN OF THE GRADUATE SCHOOL
ACKNOWLEDGEMENTS
This study was part of a project conducted by the Institute of
Coastal and Marine Resources which was funded by Texasgulf Inc. ICMR
and the Biology Department of East Carolina University provided the
equipment and facilities for successful completion of tni s project.
This study would not have been possible without the early guidance and
direction from the late Dr. Thomas J. Lawson.
I would like to thank Dr. Charles W. O'Rear my committee chairman
and members of my thesis committee. Dr. Mark M. Brinson, Dr. Vincent J.
Beilis Jr., and Dr. Ronald G. Hodson for their helpful comments and sug-
gesti ons.
I would also like to acknowledge Loede Harper for helping with the
data collection and processing, and Susan Holth for typing the manu-
scri pt.
Special thanks to iiy wonderful parents and B.J. for their constant
support and companionship.
TABLE OF CONTENTS
PAGE
LIST OF FIGURES v
LIST OF TABLES vi
INTRODUCTION 1
I-IATERIALS AND METHODS 4
RESULTS 10
Hydrography 10
Zooplankton 10
Benthos 10
Stomach Contents 14
Spot 14
Atlantic croaker 18
Southern flounder 21
Bay anchovy 24
Seasonality 27
Winter 27
Early spring 27
Early summer 29
Late summer 29
Late fall 32
Diet Breadth 32
Diet Overlap 36
Ivlev's Index of Electivity 36
DISCUSSION 40
SUMMARY AUD CONCLUSIONS 44
LITERATURE CITED 46
LIST OF FIGURES
Figure Page
1. Location of Bond Creek indicating the area sampled 5
2. Percent composition by dry weight of major prey con-
sumed by two species of fish collected during the day
and night in Bond Creek, Beaufort County, M.C. during
winter 1981 28
3. Percent composition by dry weight of major prey consumed
by four species of fish collected during the day and
night in Bond Creek, Beaufort County, N.C. during early
spring 1981 30
4. Percent composition by dry weight of major prey consumed
by two species of fish collected during the day and
night in Bond Creek, Beaufort County, N.C. during
early summer 1981 31
5. Percent composition by dry weight of major prey consumed
by two species of fish collected during the day and
night in Bond Creek, Beaufort County, N.C. during late
summer 1981 33
6. Percent composition by dry weight of major prey consumed
by four species of fish collected during the day and
night in Bond Creek, Beaufort County, N.C. during late
fall 1980 34
LIST OF TABLES
Table Page
1. Collection dates, temperature ranges, and seasons during
the 1980 - 1982 Bond Creek study. The data set for each
date is indicated 6
2. Seasonal surface (S) and bottom (B) water temperature,
salinity, and dissolved oxygen (D.O. ) values from
Bond Creek during 1980 - 1982 studies 11
3. Mean densities (#/in +_ 1 S.E. ) of zooplankton collected
during the day and night from two seasons in Bond
Creek 12
4. Mean densities (#/m ± 1 S.E.) of benthic invertebrates
by season collected from Bond Creek (total area
sampled = 0.07m^) 13
5. Seasonal relative abundance (%) by number of benthic
invertebrates collected from Bond Creek 15
6. Percentage of occurrence of different food items in
the stomachs of spot containing food, collected during
diel studies from Bond Creek during four seasons 16
7. Percent dry weight of the stomach contents of spot from
Bond Creek. Mean lengths of spot in mm are indicated... 17
8. Percentage of occurrence of different food items
in the stomachs of Atlantic croaker containing food,
collected during diel studies from Bond Creek during
five seasons 19
9.Percent dry weight of the stomach contents of Atlantic
croaker from Bond Creek. Mean lengths of Atlantic
croaker in mm are indicated 20
10. Percentage of occurrence of different food items in
the stomachs of southern flounder containing food,
collected during diel studies from Bond Creek during
five seasons 22
11. Percent dry weight of the stomach contents of southern
flounder from Bond Creek. Mean lengths of southern
flounder in mm are indicated 23
12. Percentage of occurrence of different food items in
the stomachs of bay anchovy containing food, collected
during diel studies from Bond Creek during four
seasons 25
13. Percent dry weight of the stomach contents of bay
anchovy from Bond Creek. Mean lengths of bay anchovy
in nm are indicated 26
14. Diet breadths of juvenile fish in Bond Creek based
on mean percent dry weight of stomach contents 35
15. Diet overlap between juvenile fish in Bond Creek
based on mean percent dry weight of stomach
contents 37
16. Relative abundance {%) by number of selected prey
items found in the gut (PG) and the environment
(PE) and Ivlev's index of electivity (E) 39
INTRODUCTION
The juvenile fish communities of shallow estuarine tributaries
in the southeastern United States are composed of transient species
along with a few permanent resident species (Miller et al. 1984).
These transient species immigrate into the shallow tributaries as
postlarvae and maintain residency until they emigrate as juveniles
(Carr and Adams 1973, Chao and Musick 1977, and Ueinstein 1979).
During this residence time, competition for habitat and food re-
sources is great (Stickney et al. 1975; Currin et al. 1984). For
these abundant populations to coexist, a resource partitioning or
niche separation must occur.
Christiansen and Fenchel (1977) described ni ctie separation of
populations using three main dimensions involving time, habitat, and
resource. Feeding-habit studies involving several species of fish
have documented various factors involved in resource partitioning
including differences in feeding periods (Kjelson et al. 1975; Hobson
and Chess 1976), size differences and functional morphologies (Chao
and Musick 1977; Keast 1985), habitat preference (Thorman 1983), and
food partitioning (Kinch 1979; Galat and Vucinich 1983; MacDonald and
Green 1986). However, as Schoener (1974) suggested, a complete un-
derstanding of resource partitioning involves examination of the
whole community including analysis at the individual level as well as
the population level and not just a documentation of the differences
in diet among the species. An understanding of the food resources
available for each size class of all species that co-occur must be
2
included. Simple documentation of prey items eaten by each species
and size class during each season ignores competition among the spe-
ci es and size classes.
Trawl data collected from a small tributary of the Pamlico River
in 1980 indicated that three transient species and one resident spe-
ci es comprised over 90% of the total juvenile fish catch (Lawson
1981). These four species were spot (Leiostomus xanthurus), Atlantic
croaker (Miavopogonias undulatus), southern flounder (Pavalïahthys
tethostigma), and bay anchovy (Anahoa mitahilli). The diets and
modes of feeding of these four species have been extensively documen-
ted. Spot and Atlantic croaker have been classified as opportunistic
feeders utilizing the most abundant and available prey. Prey items
f1o9u7n9d). in the stomach have included copepods, polychaetes, and bivalvesiphons (Darnell 1958; Kjelson et al. 1975; Stickney et al. 1975).Southern flounder are more selective in their feeding habits fre-quently choosing nysids and fish (Darnell 1958; Powell and SchwartzAnchovies have been described as zooplankti vores and utilize
prey including copepods and mysids (Detwyler and Houde 1970; Schwartz
9180).
Unfortunately, most of the studies only documented diet differ-
enees among the species with seasonal variations. Many studies at-
tempted to explain the resource partitioning but failed to have the
ancillary biological data necessary to answer questions involving
prey abundances, diel effects, or possible ontogenetic changes in
feeding habits.
3
The purpose of this study was to determine the feeding habits of
these four species of juvenile fish in a North Carolina estuary and
to assess any niche separation or overlap among them. This asses-
sment involved the testing of one major hypothesis and three sub-
hypotheses:
1) Niche separation exists among the species as a result
of differences in diets.
A) Species exhibit seasonal differences in diets.
B) Species exhibit diel differences in diets.
C) Species exhibit varying degrees of selectivity in diet.
MATERIALS AND METHODS
This study was conducted in the midreaches of Bond Creek which
is located near the mouth of South Creek, a major tributary of the
Pamlico River (Figure 1). Eight sampling trips were made between
October 1980 and October 1982. Four species of juvenile fish (spot,
Atlantic croaker, southern flounder, and bay anchovy) were collected
during five consecutive seasons through December 1981. Zooplankton
were collected during March and June 1981 while benthos were sampled
over five consecutive seasons from September 1981 through October
1982. Since aquatic organisms are often dependent upon water temper-
ature throughout several life stages and not on the calendar dates,
the collection dates were categorized into seasons according to water
temperature (Table 1).
For stomach analyses, a di el series of trawl samples was taken
during each season. Sampling times were scheduled so that each diel
series coincided with the two predicted lunar high and low tides dur-
i ng the day and night.
Juvenile fish were collected with a 4.0-m, two-seam trawl made
of 6.4-imi bar mesh equipped with a cod end bag of 3.2-mm mesh. The
stomachs of all large fish (> 25mm) were injected with a buffered
formalin solution within approximately 1 h after collection to stop
digestion. Then the entire trawl catch was preserved in a 10% buf-
fered formalin solution.
Zooplankton were also collected during the diel series using two
250-um mesh conical nets with a mouth area of 800 cm . The nets were
5
Figure 1. Location of Bond Creek indicating the area sampled.
6
Table 1. Collection dates, temperature ranges, and seasons during the
1980 - 1982 Bond Creek study. The data set for each date is
indicated.
Collection Date “C Season Data Set
October 27-28, 1980 13.0-14.6 Late Fall Stomach contents
March 5-6, 1981 11.5-14.0 Early Spring Stomach contents
Zooplankton
June 8-9, 1981 26.0-29.2 Early Summer Stomach contents
Zooplankton
September 22-23, 1931 21.0-25.0 Late Summer Stomach contents
Benthos
December 21-22, 1981 3.2 - 5.8 Vii nter Stomach contents
Benthos
April 20-21, 1982 18.4-19.8 Late Spring Benthos
August 17-13, 1902 27.0-29.6 Summer Benthos
October 20-21, 1982 17.6-18.6 Early Fall Benthos
7
mounted on rectangular alurninum frames welded together so that they
could be towed simultaneously. Replicate samples were collected from
just below the water surface and, using an aluminum sled, from just
above the creek bottom. Each net v;as equipped with a General Ocean-
i cs flowmeter provided with a slow speed rotor. The two nets were
towed for 2.5 min at a speed of approximately 2 km/h, after which
their contents were pooled. All samples were preserved in 10% buf-
fared formalin.
Benthos were sampled using a 15.2 x 15.2 x 22.9-cm Ekman grab.
Triplicate benthic samples were taken with each benthic sample con-
si sting of the pooled contents of three grabs washed through a 500-wm
mesh sieve and preserved in formalin. The total area sampled was ap-
p
proximately 0.07m .
Surface and bottom temperature, salinity, and dissolved oxygen
concentration were measured during each series of sample collec-
tions. A Yellow Springs Instrument Model 33 STC meter was used to
measure salinity and temperature, while a Model YSI 51A oxygen meter
was used to measure dissolved oxygen concentration.
For each set of trawls, three specimens of each species were se-
lected and their standard length measured to the nearest mm. Each
was then weighed to the nearest 0.1 g. The stomachs of these indi-
vi duals were then removed for content analysis. The contents were
sorted in a Petri dish, identified to the lowest taxonomic level
practicable, food items enumerated and then oven dried at 60°C for 24
h.
The zooplankton samples were subsampled volumetri cally. All or-
8
gani sms were then sorted and identified to the lowest taxonomic level
practicable. The volume of water filtered by each net was then cal-
O
culated and the number of organisms/m calculated for each taxa.
Benthic samples were emptied onto a 500mesh sieve for thor-
ough washing and returned to the jar for staining with Rose Bengal.
All organisms were sorted, identified to the lowest taxonomic level
p
practicable and counted. Organisms were then reported in number/m .
Stomach contents were reported in four major food groups as in
Chao and Musick (1977) and Hodson et al. (1981): macrozooplankton,
microzooplankton, benthos, and fish. Unidentifiable material
(organics) and plant debris (detritus) were also noted. Frequency of
occurrence, percent composition by number, and percent composition by
dry weight were determined.
Diet overlap ) which indicates the extent to which two par-
ticular species are utilizing the same prey items was calculated for
each pair of fish using Schooner's index (Keast 1985):
- 0.5
t=l
in this equation P is the proportion of the i prey consumed by
iÿJl
species j, and is the proportion of the i prey consumed by
species k.
Diet breadth (B) which indicates the relative range of prey
eaten was also calculated according to the method described by Keast
(1985) :
B = l/{Pi)^
9
where is the proportion of the prey category.
Ivlev's index of electivity (E), as described by Strauss (1979),
was used in comparing food found in the stomach to that available for
consumption. This index of electivity is stated as:
where r^ is the proportion of the prey in the gut, and the
proportion of the same prey in the environment.
An analysis of variance was used to determine if any differences
observed in feeding patterns according to season, time of feeding, or
prey preference vyere significant (P _< 0.05). Prior to these analy-
ses, an arc sine square root transformation was performed to achieve
uniform variance of percentage data.
RESULTS
Hydrography
The coldest water temperature recorded was 3.2°C during the win-
ter of 1981, while the warmest temperature was 29.6°C recorded during
the summer of 1982 (Table 2). Salinity fluctuated yearly with high
values around 13 and 14 ppt during 1981 and low values around 7 and 8
ppt in 1982. Dissolved oxygen was inversely related to temperature
with the low of 1.2 ppm recorded at night during the early summer.
The highest values were observed during the day in the winter of 1982
and ranged between 10 and 13 ppm.
Zooplankton
Calanoid copepods {Aaavtia tonsa and Euvytemova affinis) dom-
inated the zooplankton samples. Mean densities of approximately
CO
2.3x10 /m and 1.6x10 /m were found during early spring and early
summer (Table 3). Other abundant taxa included mysids, polychaete
larvae, and barnacle nauplii during early spring and barnacle
nauplii, grass shrimp, and harpacticoid copepods during early sum-
mer. The densities of these abundant taxa each averaged between
approximately 2.0xl0^/m^ and 5.0xl0^/m^.
Benthos
The dominant benthic organism throughout the study was
chironomid larvae which had a peak abundance in late spring (Table
4). These were followed by capitellid polychaetes in early fall, and
the spionid polychaetes in winter and early fall. Diversity was
greatest during vrinter when 13 taxa were collected followed by late
11
Table 2. Seasonal surface (S) and bottom (B) water temperature, salinity,
and dissolved oxygen (0.0.) values from Bond Creek during 1980 -
1982 studies.
Tide Status
Day Hi qh Day Low Ni ght Hi qh Niqht Low
Season Parameter S B SB SB S B
Late Fall '80 Temp. 13.8 14.0 14.1 14.6 13.2 14.0 13.0 14.0
Sal. 9.8 10.0 11.0 12.0 7.5 8.2 9.5 10.0
D.O. 10.6 10.4 9.5 10.2 8.5 9.0 9.5 10.0
Early Spri ng '81 Temp. 12.0 11.5 11.9 12.0 13.9 14.0 13.0 13.0
Sal. 14.4 13.8 13.1 13.2 13.2 13.7 13.5 13.0
D.O. 10.8 11.8 9.1 9.2 10.0 10.0 10.8 9.8
Early Summer '81 Temp. 26.5 26.0 29.2 26.0 28.5 28.0 26.8 26.0
Sal. 12.2 13.6 10.0 13.8 9.0 12.5 8.8 12.4
D.O. 8.7 4.6 9.4 8.0 10.3 9.0 3.6 1.2
Late Summer '81 Temp. 21.5 21.0 25.1 23.2 25.0 23.4 23.0 22.9
Sal. 14.0 13.8 14.4 12.6 13.5 11.1 13.6 13.5
D.O. 4.4 6.9 7.8 7.6 7.4 6.0 7.9 7.7
Wi nter '31 Temp. 3.2 4.5 3.5 4.0 4.6 5.2 5.4 5.8
Sal. 13.6 15.5 15.0 15.8 14.2 13.5 14.4 12.6
D.O. 12.5 9.9 12.2 12.3 12.4 11.9 11.5 10.0
Late Spri ng '82 Temp. 19.8 19.2 19.2 19.2 19.5 19.2 19.0 18.4
Sal. 6.8 6.8 7.2 7.2 7.4 7.0 7.2 6.8
D.O. 9.0 6.1 8.2 6.5 7.0 4.9 7.7 4.7
Summer '82 Temp.. 29.6 29.2 27.8 28.0 27.8 27.0 28.0 27.8
Sal. 8.2 8.3 7.6 7.5 8.0 8.0 8.2 8.2
D.O. 7.7 7.4 - - 5.9 5.7 8.0 7.6
Early Fall ' 82 Temp. 18.1 17.8 18.6 18.1 18.6 18.1 17.0 18.0
Sal. 8.0 8.2 8.4 8.6 8.2 8.4 7.4 8.1
D.O. 12.0 12.3 8.5 8.6 5.4 5.5 4.8 5.1
12
O
Table 3. ¡lean densities (#/in 1 S.E.) of zooplankton collected during
the day and night from two seasons in Bond Creek.
Early Spring Early Summer
Taxon Day Ni ght Day Ni ght
Calanoid copepods (Day) 123,378 + 108,266 l.i309,422 + 2,164,205
(Night) 330,015 ^ 181,183 1, 296,129 571,693
My si ds 57 + 152 1C1,239 28,494 50 + 130 1049 2155
Polychaete larvae 3006 + 3039 7490 +_ 11,015 5 ± 8 8 18
Barnacle nauplii 3445 + 3544 380 1045 2715 ^ 5344 4131 6903
Grass shrimp 0 + 0 1515 ¿ 4200 3042 5621 1289 1339
Harpacticoid copepods 130 + 310 550 903 23 66 4233 7867
Barnacle cypri ds 341 + 471 69 194 1149 ^ 2498 797 1124
Crab zoea 0 + 0 0 L 0 283 396 768 +_ 857
Cyclopoid copepods 0 + 0 298 842 0 ± 0 530 1003
Ostracods 20 + 55 0 + 0 0 + 0 0 + 0
13
O
Table 4. Mean densi ties(#/!n ± 1 S.E.) of benthic invertebrates by season
collected from Bond Creek (total area sampled = 0.07m^).
Phylurn 1981 1982
Speci es/Taxon Late Wi liter Late Summer Early
Summer Spring Fall
Rhynchocoela
N erne r tea n 5±8 14±14 33134
Mol 1usca
Pel ecypoda
Maooma sp. 5±8 10±17 1961133 918
Maaomx siphons 10117
Annelida
Polychaeta
Phyllodoci dae 14±14
fJerei dae 14±14 24±42 24117
Capitellidae 9±3 11001332 19131234 323911244
Spi oni dae 450±356 27501872 10001145 25831739
Amp hare ti dae 77136 72150
Oligochaeta
Nai di dae 4591502 513
Tubi fi ci dae 518 513
Arthropoda
Insecta
Chi ronomi dae 1. 1961133 13111296 49361395 5691187
Chironomidae p. 5±8 29114
Crustacea
Ostra COda 513
Harpacti coi da 518
Covophium sp. 24130 513
Mysidopsis higelowi 10±17 518 62136
14
spring when 10 taxa were collected. Summer grabs were void of ben-
thic organism.
During the late summer, the spionids comprised over 64% of the
total number of benthic invertebrates collected, followed by chiro-
nomi d larvae with a percent relative abundance over 28% (Table 5).
During the winter spionids comprised over 47% while chirononiid larvae
and capitel lids comprised 23% and 19% of the total number respective-
ly. Late spring grabs v;ere dominated by chironomid larvae with a
percent relative abundance over 60%. Capitel lids comprised over 23%
and spionids over 12% of the total number collected. The early fall
grabs were dominated by capitel lids at 50% and spionids at 40%.
Stomach Contents
Spot - Stomachs of 37 spot collected during four seasons were
examined. Food items were found in 92% (34) of these stomachs (Table
6). Polychaetes, ostracods, and nematodes were found in the stomachs
during all seasons while mysids, chironomids, harpacti coi ds, cala-
noids, cyclopoids, oli gochaetes, isopods and bivalve siphons were
present in the stomachs during three of four seasons.
Seasonally, harpacti coi ds, ostracods, nematodes, and chironoi.iid
larvae were found in at least 75% of the stomachs containing food
during late fall. However, mysids which occurred in only 62% of the
stomachs made up over 40% of the contents when percent dry weight was
calculated (Table 7). Chironomid larvae and fish comprised between
19% and 15% of the dry weight. Polychaetes and calanoids were found
in 60% and 40% of the stomachs respectively while polychaetes, cala-
noids, and isopods each comprised between 31% and 25% of the dry
15
Table 5. Seasonal relative abundance (%) by number of benthic inverte-
brates collected from Bond Creek.
1981 1982
Phyl urn Late Late Early
Sped es/Taxon Summer Wi nter Spring Summer Fall
Rhynchocoela
Nemertean Q.72 0,24 0.40
Mol lusca
Pel ecypoda
Maaoma sp. 0.72 0.17 2.39 0.14
Macona si phons 0.15
Annelida
Polychaeta
Phyl 1 odoci dae 0.24
fJerei dae 2.02 0.41 0.30
Capitellidae 1.30 13.97 23.36 49.75
Spi oni dae 64.84 47.43 12.21 39.75
Amp hare ti dae 1.33 0.88
01 i gochaeta
Nai di dae 7.92 0.06
Tubi fi ci dae 0.09 0.06
Arthropoda
Insecta
Chi ronomi dae 1. 28.24 22.61 50.28 8.74
Chironomidae p. 0.72 0.44
Crustacea
Ostracoda 0.09
Harpacticoi da 0.08
Covophium sp. 0.41 0.06
Mysidopsis higelowi 1.44 0.09 0.95
16
Table 6, Percentage of occurrence of different food items in the stomachs
of spot containing food, collected during die! studies from
Bond Creek during four seasons.
Season Seasons
Food Item Late Early Early Late Combi ned
Fall Spring Summer Summer
Macrozooplankton
Mysids 62.5 8.3 33.3 26.5
Chironomid larvae 75.0 58.3 33.3 47.1
Dipteran pupae 11.1 2.9
Microzooplankton
Harpacti coi ds 100.0 8.3 55.6 41.2
Calanoi ds 40.0 41.7 11.1 23.5
Cyclopoids 25.0 20.0 44.4 26.5
Copepodites 55.6 8.8
Ostracods 87.5 20.0 8.3 11.1 29.4
Barnacle cyprids 8.3 2.9
Benthos
Polychaetes 25.0 60.0 75.0 44.4 52.9
01igochaetes 12.5 25.0 11.1 14.7
Amphi pods 37.5 11.1 11.8
Isopods 20.0 8.3 11.1 8,8
Mema todes 75.0 20.0 66.7 38.9 67.6
Bivalve siphons 20.0 75.0 11.1 32.4
Fi sh
Gobi es 12.5 2.9
Seal es 33.3 11.1 14.7
Organics 75.0 40.0 25.0 66.7 50.0
Detritus 25.0 66.7 55.6 44.1
Al gae 25.0 5.9
Number fish examined 9 7 12 9 37
Number fish with food 8 5 12 9 34
17
Table 7. Percent dry weight of the stomach contents of spot from Bond
Creek, [lean lengths of spot in mm are indicated.
Season
Late Early Early Late Seasons
Food Item Fall Spring Summer Summer Combi ned
X =104 7=24 7=63 7=89
Macrozooplankton
My si ds 40.34 0.04 77.08 43.51
Chironomid larvae 18.86 8.85 2.32 9.16
Dipteran pupae 1.42 0.58
Microzoopiankton
Harpacti coi ds 2.80 0.04 0.04 0.91
Calanoids 28.20 0.20 0.03 0.20
Cyclopoids 1.54 2.56 0.37 0.62
Copepodites 0.14 0.06
Ostracods 0.96 2.56 0.04 0.03 0.32
Barnacle cyprids 0.04 0.01
Benthos
Polychaetes 0.42 30.77 41.73 16.74 19.10
Oligochaetes 0.38 0.12 0.03 0.16
Amphi pods 2.69 0.57 1.04
Isopods 25.64 0.40 0.28 0.35
Nematodes 0.23 2.56 1.04 0.48 0.58
Bivalve siphons 2.56 46.90 0.03 13.53
Fi sh
Gobi es 15.37 4.61
Scales 0.16 0.03 0.06
Organics 16.25 5.13 0.12 0.17 5.01
Detri tus 0.08 0.32 0.14 0.17
Al gae 0.08
18
weight during the early spring. Polychaetes, bivalve siphons, and
nematodes were present in over 66% of all the stomachs with bivalve
siphons and polychaetes each comprising over 41% of the dry weight of
all the stomach contents during early summer. Nematodes were the
dominant organisms during late summer and were present in almost 89%
of the stomachs. Mysids were found in only 33% of the stomachs but
comprised over 77% of the dry weight.
Overall, nematodes, polychaetes, and chironomid larvae were
found most frequently in the stomachs of spot, while nysids dominated
the percent dry weight at over 43% followed by polychaetes (19%) and
Pi valve siphons (14%).
No significant difference among ttie major food groups consumed
by spot was observed (P <_ 0.Ü5; F=0.102). This suggest that spot
utilized a wide range of prey and infers an opportunistic feeding be-
havi or.
Atlantic croaker - Stomachs of 51 croaker collected during five
seasons were examined and over 88% (45) contained food (Table 8).
Mysids, chironomid larvae and polychaetes were present in the
stomachs during four of five seasons while harpacti coi ds, calanoids,
and amphipods were found in the stomachs during three of five sea-
sons.
Seasonally, irysids and chironomid larvae were found in all sto-
machs that contained food during late fall. Mysids comprised almost
49% of the dry weight while chironomid larvae comprised 27% (Table
9). Calanoids were present in over 77% of the stomachs and accounted
for 48% of the total dry weight during early spring while mysids.
19
Table 8. Percentage of occurrence of different food items in the stomachs
of Atlantic croaker containing food, collected during di el
studies from Bond Creek during five seasons.
Season
Food Items Late Early Early Late Seasons
Fall Spring Summer Summer Winter Combi ned
Macrozooplankton
My si ds 100.0 33.3 88.9 20.0 48.9
Chironomid larvae 100.0 11.1 75.0 100.0 64.4
Dipteran pupae 30.0 8.3 6.7
Palaemonid zoea 8.3 2.2
Crustacean zoea 8.3 2.2
Microzooplankton
Harpacticoi ds 20.0 33.3 8.3 13.3
Calanoids 77.7 41.7 40.0 31.1
Cyclopoids 8.3 2.2
Ostracods 20.0 11.1 6.7
Benthos
Polychaetes 20.0 22.2 75.0 88.9 46.7
Oligochaetes 30.0 75.0 26.7
Amp hi pods 10.0 22.2 11.1 6.7
Isopods 11.1 4.4
Nematodes 25.0 6.7
Bivalve siphons 75.0 11.1 22.2
Fi sh
Anchovi es 11.1 2.2
Gobi es 10.0 11.1 4.4
Menhaden 22.2 4.4
Seal es 16.7 11.1 6.7
Organics 70.0 11.1 58.3 88.9 40.0 55.6
Detri tus 10.0 25.0 77.8 24.4
Sand 10.0 8.3 4.4
A1 gae 40.0 44.4 17.3
Number fi sh exami ned 10 9 12 9 11 51
Number fish with food 10 9 12 9 5 45
20
Table 9. Percent dry weight of the stomach contents of Atlantic croaker
from Bond Creek. Mean lengths of Atlantic croaker in mm are
i ndi cated.
Season
Late Early Early Late Seasons
Food Item Fall Spri ng Summer Summer Winter Combined
x=126 x=36 ><lII x=137 x=28
Macrozooplankton
My si ds 48.80 13.32 64.44 20.00 55.64
Chironomid larvae 27.00 4.61 33.52 4.57 13.83
Dipteran pupae 3.37 2.61 1.31
Palaemonid zoea Ü.07 <0.01
Crustacean zoea 0.07 <0.01
Microzooplankton
Harpacti coi ds 0.02 13.82 0.07 0.10
Calanoids 47.93 0.91 40.00 0.36
Cyclopoids 0.07 <0.01
Ostracods 0.02 0.01 0.01
Benthos
Polychaetes 0.02 14.29 17.90 5.12 3.96
01igochaetes 0.59 0.04
Amp hi pods 0.92 0.30 0.18
Isopods 0.01 0.40 0.24
Nematodes 0.20 0.01
Bivalve siphons 43.20 0.01 1.97
Fi sh
Anchovi es 7.96 4.73
Gobi es 4.04 2.10 2.68
Menhaden 13.88 8.25
Scales 0.20 0.01 0.01
Organics 16.66 4.61 0.46 1.14 40.00 6.62
Detri tus 0.01 0.13 0.04 0.03
Al gae 0.03 0.02 0.02
21
harpacticoi ds, and polychaetes each comprised nearly 14% of the total
dry weight. Chironomid larvae, polychaetes, oligochaetes, and bi -
valve siphons, each occurred in 75% of the stomachs containing food
during early summer. The percent dry weight was dominated by bivalve
siphons at 43%, chironomid larvae at 34%, and polychaetes at 18%.
During late summer, chironomid larvae, mysids, and polychaetes were
each present in over 89% of the stomachs that contained food. Mysids
dominated by percent dry weight at over 64%. Calanoids and mysid
remains were the only food items found during winter with calanoids
comprising the higher percent dry weight at 40%.
Overall, chironomid larvae were present in 64% of the stomachs,
while mysids were found in 49% and polychaetes 47%. Percent dry
weight was dominated by nr/sids at over 55%.
Analysis of variance showed no significant difference in diet by
major food groups found in the stomachs (P _< 0.05; F=0.0503). This
suggest there was a wide variety of prey consumed by Atlantic
croaker.
Southern flounder - Stomachs of 21 southern flounder collected
during five seasons were examined. Food was found in 67% (14) of
these stomachs (Table 10). Mysids and fish dominated the prey items
and were found in the stomachs during three of five seasons.
Mysids were found in over 87% of the stomachs, while a pi sci vor-
ous tendency was noted in 25% during late fall. Percent dry weight
indicated mysids comprised over 65% of the total contents, while fish
remains comprised over 30% (Table 11). Mysids were the only food
items found during early spring. Mysids were the dominant food items
22
Table 10. Percentage of occurrence of different food items in the
stomachs of southern flounder containing food, collected
during di el studies from Bond Creek during five seasons.
Season
Food Item Late Early Early Late Seasons
Fall Spring Summer Summer Winter Combined
Macrozooplankton
My si ds 87.5 100.0 66.7 78.6
Benthos
Tanaids 50.0 7.1
Fi sh
Gobi es 25.0 7.1
Uni denti fi ed 12.5 100.0 21.4
Seal es 33.3 7.1
Organi cs 37.5 21.4
Detri tus 12.5 7.1
Number fi sh exami ned 9 2 6 2 2 21
Number fish with food 8 2 3 0 1 14
23
Table 11. Percent dry weight of the stomach contents of southern flounder
from Bond Creek. Mean lengths of southern flounder in mm are
i ndi cated.
Season
Late Early Early Late Seasons
Food Item Fall Spring Summer Summer Winter Combi ned
x=120 x=118 x=69 x=100 x=117
Macrozooplankton
My si ds 65.59 99.97 99.45 64.26
Benthos
Tanaids 0.03 0.01
Fi sh
Gobi es 8.95 4.34
Uni denti fi ed 21.92 100.00 29.66
Scales 0.55 0.01
Organi cs 2.12 1.03
Detritus 1.42 0.69
24
found during early summer being present in 67% of the stomachs. They
comprised 99% of the total dry weight. Only two flounder were col-
lected during late summer and the stomachs of both fish were empty.
During the winter, only two flounder were collected and only one
stomach contained food which consisted of unidentified fish parts.
Overall, mysids were present in almost 79% of the stomachs that
contained food while fish remains were found in over 21%. Mysids
comprised over 64% of the total dry weight with fish remains compris-
ing another 30%. Analysis of variance indicated a significant di f-
ference among major food groups consumed (P 0.05; F=0.006). This
infers that southern flounder prefer macrozooplankton (mysids) and
fish over the microzooplankton and benthos.
Bay anchovy - Stomachs of 34 bay anchovies collected during four
seasons were examined. Food was found in 71% (24) of the stomachs
(Table 12). Calanoids, ostracods, and polychaete larvae were found
i
in the stomachs during three of the four seasons.
Phytoplankton was found in over 45% of the stomachs while nysids
were found in 36% of the stomachs during late fall. Mysids comprised
over 95% of the total dry weight (Table 13). Calanoids and unidenti-
fied copepodites were the most frequent food item found during early
spring and occurred in over 62% and 87% respectively, of the stomachs
that contained food. Mysids occurred in only 12.5% of the stomachs
but comprised over 71% of the total dry weight. During late summer,
calanoids were found in 67% of the stomachs and comprised 61% of the
total dry weight. Eight anchovies were collected during winter, but
only two stomachs contained food. Calanoids, cyclopoids, and oli-
25
Table 12. Percentage of occurrence of different food items in the
stomachs of bay anchovy containing food, collected during diel
studies from Bond Creek during four seasons.
Season Seasons
Food Item Late Early Late Combi ned
Fall Spri ng Summer Wi nter
Macrozooplankton
My si ds 36.4 12.5 20.8
Chironomid larvae 33.3 4.2
Microzooplankton
Harpacticoids 9.1 50.0 20.8
Calanoids 62.5 66.7 50.0 33.3
Cyclopoids 50.0 4.2
Copepodites 87.5 29.2
Copepod eggs 12.5 4.2
Ostracods 18.2 37.5 33.3 25.0
Barnacle nauplii 33.3 4.2
Benthos
Polychaetes 9.1 12.5 33.3 12.5
01igochaetes 50.0 4.2
Isopods 12.5 4.2
Bi val ves 9.1 4.2
Phytopiankton 45.5 12.5 33.3 29.2
Organics 45.5 50.0 66.7 45.8
Number fish examined 12 10 4 8 34
Number fish with food 11 8 3 2 24
26
Table 13. Percent dry weight of the stomach contents of bay anchovy
from Bond Creek. Mean lengths of bay anchovy in mm are
i ndi cated.
Season
Late Early Late Seasons
Food Item Fall Spring Summer Wi nter Combined
7=42 7=41 x=37 x=35
Macrozooplankton
My si ds 95.31 71.03 88.22
Chirononid larvae 5.56 0.11
Microzooplankton
Harpacticoi ds 0.14 2.19 0.55
Calanoids 7.65 61.10 33.34 2.75
Cyclopoids 33.33 0.22
Co pepo di tes 3.83 0.77
Copepod eggs 0.55 0.11
Ostracods 0.29 1.64 5.56 0.66
Barnacle nauplii 5.56 0.11
Benthos
Polychaetes 1.42 5.46 5.56 2.31
Oligochaetes 33.33 0.11
Isopods 5.46 1.10
Bival ves 1.42 1.10
Phytoplankton 0.71 0.55 5.56 0.77
Organi cs 0.71 1.64 11.10 1.10
27
gochaetes were each found in 50% of the stomachs and each comprised
approximately 33% of the total dry weight.
Overall, calanoids were found in 33% of the stomachs. Copepo-
dites and phytoplankton were each found in 29% of the stomachs.
Mysids occurred in 21% of the stomachs but comprised over 83% of the
total dry weight. Although calanoids were present in numerous
stoiTachs they comprised only 3% of the total dry weight, ilo si gni f-
i cant difference was found in the major food groups consumed by bay
anchovy (P_£ 0.05; F=0.2741). However since the analysis ms based on
percent dry weight, this is misleading. The mi crozooplankton con-
sumed most often by bay anchovy do not weigh as tnuch as the larger
prey items and consequently a nonsignificance was seen.
Seasonali ty
Wi nter - The mean length (28 mm SL) of spot in tlie winter trawl
collections indicated that Atlantic croaker had immigrated into the
nursery area. They fed evenly on macrozooplankton and microzooplank-
ton and shared the microzooplankton with the 35-mm bay anchovy. The
bay anchovy also fed on young benthic organisms during the day where
the spot did not (Fig. 2). Southern flounder fed only at night and
had no competition for their preferred diet of fish.
There was no significant difference in day/night preference for
selection of the four major food groups.
Early spring - The small fish that migrated into the nursery
areas during late winter had taken up residence by early spring with
an increase in mean length. Spot (24 mm SL) and Atlantic croaker (36
mm SL) were smaller than southern flounder (118 mm SL) that had prob-
ATLANTIC CROAKER BAY ANCHOVY
DAY
NIGHT
Figure 2. Percent composition by dry weight of major prey consumed by two species of fish collected
during the day and night in Bond Creek, Beaufort County, N.C. during winter 1981.
29
ably overwintered in the creeks and also smaller than the estuarine
spawned bay anchovy (41 mm SL). The small spot utilized microzoo-
plankton and benthos exclusively while Atlantic croaker basically
consumed microzooplankton with some macrozooplankton and benthos
noted (Fig. 3). The southern flounder maintained a preference for
macrozooplankton while the bay anchovy consumed food items from all
the major food categories except fish.
Figure 3 also displays diel differences in food selection of all
four species collected during early spring. However, the results of
an analysis of variance suggests there is no significance in the diel
differences in the basic food groups utilized.
Early Sumimer - Growth of spot (63 rnm SL) and Atlantic croaker
(66 mm SL) and the immigration of young southern flounder (69 mm SL)
forced fish of similar size to coexist. Food partitioning was evi-
dent by spot predominantly utilizing benthos, while Atlantic croaker
utilized benthos at night but switched to macrozooplankton during the
day (Fig. 4). Southern flounder again fed extensively on the macro-
zooplankton.
The selection of food for the two species collected during both
day and night in early summer did not indicate any significant diel
differences.
Late summer - The mean length range of juvenile fish collected
during late summer was wider than at anytime of the year. Spot
averaged 89 iTim, Atlantic croaker averaged 137 mm while southern
flounder had grown to 100 mm. The ubiquitous bay anchovy averaged
around 37 inm in length. Prey items consumed were similar for spot
SPOT ATLANTIC CROAKER SOUTHERN FLOUNDER BAY ANCHOVY
NIGHT
UJ
Figure 3. Percent composition by dry weight of major prey consumed by four species of fish collected o
during the day and night in Bond Creek, Beaufort County, N.C. during early spring 1981.
SPOT ATLANTIC CROAKER
DAY
MICRO.
NIGHT
U)
Figure 4. Percent composition by dry weight of major prey consumed by two species of fish collected
during the day and night in Bond Creek, Beaufort County, N.C. during early summer 1981.
32
and Atlantic croaker during the day with both extensively utilizing
macrozooplankton (Fig. 5). Partitioning was more evident at night
with spot switching to benthos and Atlantic croaker showing a primary
piscivorous habit in addition to a secondary macrozooplankton and
benthos preference. Bay anchovy fed mainly on microzooplankton while
the southern flounder examined did not feed.
Late fall - During the fall and prior to emigration, the average
length increased to 104 mm for spot, 126 mm for Atlantic croaker, 120
mm for southern flounder, and 42 mm for bay anchovy. All species
predominantly utilized macrozooplankton as their main prey (Fig.
6). Spot and southern flounder diets however v/ere more diverse and
included a secondary piscivorous habit.
No day/night differences for any species were found in food pre-
ference. The major food chosen during the day was also the preferred
diet at night.
Diet Breadth
Diet breadth indicates the relative range of prey eaten. High
values indicate a wide range of diet while low values near 1.0 sug-
gest exclusive use of one prey item. Highest diet breadth values
were observed for spot and Atlantic croaker and lowest for southern
flounder and bay anchovy (Table 14). Diet breadth for spot was high-
est during late fall and early spring when numerous prey items were
chosen in large quantities and lowest during late summer when mysids
and polychaetes made up the bulk of the diet. Diet breadth of Atlan-
tic croaker was consistently high throughout the study also indica-
ting a wide use of prey items. Diet breadth for southern flounder
SPOT ATLANTIC CROAKER
.MICRO.
NIGHT
Figure 5. Percent composition by dry weight of major prey consumed by two species of fish collected
during the day and night in Bond Creek, Beaufort County, N.C. during late summer 1981.
SPOT ATLANTIC CROAKER SOUTHERN FLOUNDER BAY ANCHOVY
NIGHT
Figure 6. Percent composition by dry weight of major prey consumed by four species of fish collected
during the day and night in Bond Creek, Beaufort County, N.C. during late fall 1980.
35
Table 14. Diet breadths of juvenile fish in Bond Creek based on mean per-
cent dry weight of stomach contents.
Season Spot Atlantic croaker Southern flounder Bay anchovy
Late Fall 4.00 2.93 2.05 1.10
Early Spri ng 4.08 3.42 1.00 1.93
Early Summer 2.49 3.01 1.01 -
Late Summer 1.61 2.24 0.00 2.49
Wi nter - 2.78 1.00 1.80
15-Month Avg. 3.89 2.90 1.26 1.83
36
was highest during late fall when a dual feeding habit was noted;
however, this was substantially less than for both spot and Atlantic
croaker. During early spring, early summer, and winter, the diet
breadth of southern flounder was near 1.00 which indicated the utili-
zation of a single food item (either mysids or fish). Diet breadth
of bay anchovy was highest in late summer with microzooplankton being
dominant and lowest in late fall with extensive use of inysids as a
food source. Overall, the diet breadth of bay anchovy was slightly
higher than for southern flounder but substantially lower than for
both spot and Atlantic croaker.
Diet Overlap
Diet overlap values between individual fish pairs were greater
than 0.60 for 5 of the 6 cases indicating utilization of similar prey
items (Table 15). The spot-bay anchovy combination was the lone ex-
ception at 0.50. This resulted from spot utilizing a range of prey
items with few nri crozoopl ankton eaten which are the basic diet of bay
anchovy. The Atlantic croaker-southern flounder combination had the
highest diet overlap value at 0.75 which indicated the intensive use
of mysids by both species as a basic food source. The spot-Atlanti c
croaker combination also indicated a high diet overlap at 0.68 which
resulted from both frequently consuming mysids, chironomid larvae and
polychaetes.
Ivlev's Index of Electivity
Four dominant food categories were chosen for evaluation of
electivity. Proportions of calanoids, polychaetes, mysids, and chir-
onomi d larvae found present in the environment were compared with
37
Table 15. Diet overlap between juvenile fish in Bond Creek based on mean
percent dry weight of stomach contents.
Species Overlap value
Spot - Atlantic croaker 0.68
Spot - southern flounder 0.61
Spot - bay anchovy 0.50
Atlantic croaker - southern flounder 0.74
Atlantic croaker - bay anchovy 0.61
Southern flounder - bay anchovy 0.65
38
proportions in the gut of the selected fish species. Spot and Atlan-
tic croaker in late summer and southern flounder in both early spring
and early summer displayed electivity values that indicated active
selection of mysids as their prey (Table 16). Conversely, spot and
Atlantic croaker in early summer and southern flounder in both early
spring and early summer displayed electivity values that suggested
avoidance of calanoid copepods as their prey. The slightly negative
electivity of bay anchovy towards calanoid copepods is somewhat mis-
leading. High relative abundance percentages of calanoids in the
environment skew the values towards the negative/avoidance side.
Spot during late summer displayed an electivity suggesting
avoidance or i naccessabi li ty of polychaetes while Atlantic croaker
displayed similar negative values towards chi ronomi d larvae.
39
Table 16. Relative abundance (%) by number of selected prey items found in
the gut (PG) and the environment (PE) and Ivlev's index of
electivity (E).
Calanoi ds Polychaetes I'Vsi ds Chi ronomi ds
PG PE E PG PE E PG PE E PG PE
Spot
Early spring 36,54 94.31 -.44
Early sumrer 0.70 99.36 -.99
Late sunier 6.12 68.16 I CO 22.70 1.44 +.88
Atlantic croaker
Early spnng 32.50 94.31 -.07 2.50 2.17 +.07 6.25 2.13 +.49
Early sumer 11.43 99.36 -.79
Late simmer 79.91 1.44 +.96
Southern flounder
Early spring 0.00 94.31 -1.00 78.57 2.13 +.95
Early sumer 0.00 99.36 -1.00 100.00 0.03 +1.00
Bay anchovy
Early spring 63.28 94.31 -.20 4.47 2.17 +.35
Late sinrer 46.00 99.36 -.37
DISCUSSION
Hydrographie parameters can affect the species composition of
estuarine ecosystems (Gunter 1961). During 1981, salinity in South
Creek and its tributaries was abnormally high due to a statewide
drought (Davis et al. 1985). Consequently, the species composition
and abundance of fish as well as prey items available may have under-
gone some shifts. However, the organisms reported in this study are
basically the same as those from similar creeks (Lawson 1981; West
1985). The hydrographic parameters reported here are in agreement
with those from creeks on the north side of South Creek (Davis et al.
1985).
Postlarval spot feed mainly on zooplankton, while larger juv-
eniles are more benthic oriented feeders (Roelofs 1954; Schwartz
1980; Hodson et al. 1983; Curri n 1984). Spot collected during early
spring in this study utilized both of these major food groups. This
dual feeding habit may reflect the morphological changes occurring in
the fish at that time and result in an ontogenetic change in their
feeding habit (Kjelson and Johnson 1976). Spot collected later in
the year became more opportunistic in their feeding behavior.
Benthos were preferred in early summer and macrozooplankton in late
summer and late fall as was found by Chao and Musick (1977) and
Koblinski and Sheridan (1979).
Small Atlantic croaker (36 mm SL) utilize zooplankton extensive-
ly prior to a shift in diet to crustaceans and polychaetes (Darnell
1953; Stickney et al. 1975; Overstreet and Heard 1973). Atlantic
41
croaker collected during the winter and early spring from this study
also utilized zooplankton extensively, while juveniles collected dur-
i ng the summer preferred bivalve siphons in addition to crustaceans
and polychaetes. These results concur with findings from Rose Bay
where bivalve siphons dominated the diet of rnany juvenile croaker
(Currin 1984). As the Atlantic croaker grew throughout the year,
macrozooplankton became more prevalent in the diet suggesting a se-
lection towards larger prey, similar to findings by Stickney et al.
(1975). A piscivorous tendency by larger juvenile Atlantic croaker
(>70 mm SL) was noted by Koblinski and Sheridan (1979) in Apala-
chicóla Bay, Florida and was supported in this study.
Juvenile southern flounder and bay anchovy collected throughout
the study did not follow the basic immigration - growth - emigration
pattern shown by spot and Atlantic croaker. Flounder collected dur-
ing winter and early spring had possibly overwintered in the creek
system. Bay anchovy which spawn all year, were basically uniform in
length during the study. Southern flounder fed on macrozooplankton
(mysids) and fish almost exclusively. This feeding habit is in
agreement with findings by Darnell (1953) and Powell and Schwartz
(1979). Smaller bay anchovy are classified as zoopl ankti vores and as
their length increases macrozooplankton become increasingly more
important (Carr and Adams 1973; Schwartz 1979). In this study,
microzooplankton dominated the stomach contents from all seasons
except late fall when mysids and phytoplankton were more prevalent.
Kinch (1979) noted a secondary piscivorous tendency among larger
anchovies which was not substantiated in this study.
42
Similar diets for all four species suggest niche overlap was
prevalent. However, spot and Atlantic croaker have wide diet
breadths during the peak growing season of their preferred prey.
This opportunistic feeding behavior allows for shifts in prey se-
lection when primary prey items become difficult to obtain. Zoo-
plankton abundances in this type of system are usually highest during
early spring when larval fish begin establishing residence in the
nursery areas (Thayer et al. 1974). Likewise (Turner 1981) has shown
that rapid growth of larval spot coincides with peak plankton produc-
ti on. Consequently, when spot and Atlantic croaker moved into Bond
Creek, zooplankton were present in great numbers and were readily
available. As these two species grew, chironomid larvae and bivalves
became iircre abundant and accessible as prey. West (1985) in his
studies of the benthos in Short Creek a tributary of South Creek also
found high densities of chironomid larvae in late fall. A seasonal
shift occurred in the diet of spot and Atlantic croaker toward these
abundant prey. When the polychaetes (capitellids and spionids) ex-
hi bi ted their highest peaks of abundance later in the year, they also
became a major contributor to the diet of these species.
Diel feeding patterns have been noted in many studies. Hodson
et al. (1981) suggested juvenile spot collected from a tidally inun-
dated marsh after their transition to the benthic feeding behavior,
fed more actively at night. Likewise, this study showed that spot
had a tendency to consume higher concentrations of benthos after
sunset during four of the five seasons. Studies from Rose Bay, a
system similar to Bond Creek, did not indicate however, any apparent
43
di el feeding pattern (Currin 1984). This shift towards benthos dur-
i ng the night provides a greater variety in diet and less competition
among these dominant fish species.
The diet overlap combination of spot-Atlanti c croaker suggested
a higher degree of diet overlap during their entire residence in the
nursery area. However, the opportunistic feeding behavior of each,
as evidenced by high diet breadths, allows both species to occupy
similar niches. Atlantic croaker and southern flounder also utilized
the same basic food group and consequently exhibited a similar high
diet overlap. This suggests stiff competition for the preferred
diet. Southern flounder, however, displayed a narrow diet breadth
and actively selected mysids during early spring and early summer and
actively avoided microzooplankton. Atlantic croaker on the other
hand consumed large numbers of calanoid copepods (microzooplankton)
in the spring and showed an affinity for mysids in the late summer
while southern flounder were scarce during this period and fed inter-
mi ttently.
It has been noted that marine larvae and juveniles show low diet
overlaps (Larouche 1932). The high diet overlap values experienced
by these estuarine species suggest that competition potentially
exists if resources were limiting, which in this creek apparently are
not. The fact that food resources from this system were seasonal in
abundance as evidenced by the high numbers of zooplankton during
spring and summer while benthos were more abundant in the late fall
and winter suggests that the food resources found in Bond Creek are
not limited.
SUMMARY AND CONCLUSIONS
Spot and Atlantic croaker are both opportunistic feeders. Younger
juvenile spot utilized nri crozoopl ankton and benthos before they switched
to the opportunistic feeding behavior as older juveniles. The young
Atlantic croaker utilized microzooplankton (calanoid copepods) exten-
si vely before they also became an opportunistic feeder as older juven-
iles. Spot displayed a diet breadth value of four while Atlantic
croaker indicated a diet breadth value near three, both of which indi-
cate a wide range of prey consumed.
Southern flounder utilized macrozooplankton (mysids) extensively
but also showed a secondary piscivorous feeding habit. Extensive uti li -
zation of the macrozooplankton occurred during those seasons when the
other species were consuming other preferred prey. A diet breadth value
near one suggests the exclusive use of a single food source. Bay ancho-
vy predmoninantly consumed zooplankton. Smaller bay anchovy(<40 mm SL)
preferred microzooplankton (calanoid copepods) while the larger fish
basically consumed macrozooplankton (mysids). A diet breadth near two
emphasized the use of both categories of zooplankton.
Zooplankton reached their peak abundance during the recruitment
period of these predatory fish. Zooplankton consequently became the
major food source during this time. The early summer growing season of
these fish coincided v/i th high densities of benthos which were exten-
sively consumed. After the benthic die off, the macrozooplankton then
became the dominant food item eaten.
Only small diel differences in the type of prey consumed was
seen. The benthos were consumed more frequently at night by spot in the
45
early spring and late summer and in the early summer by Atlantic
croaker.
Mysids were the most selected prey using Ivlev's electivity index
while the calanoid copepods were the most avoided prey except by the bay
anchovy.
The four species of fish often occupied similar niches during their
residence in the nursery area. However, a seemingly unlimited food
supply allowed these abundant fish populations to coexist.
LITERATURE CITED
Carr, W.E.S. and C.A. Adams. 1973. Food habits of juvenile marine
fishes occupying seagrass beds in the estuarine zone near Crystal
River, Florida. Trans. Am. Fish. Soa. 102:511-540.
Chao, L.N. and J.A. Musick. 1977. Life history, feeding habits, and
functional morphology of juvenile Sciaenid fishes in the York River
Estuary, Virginia. Fish. Bull. 75:657-702.
Christiansen, F.B. and T.M. Fenchel. 1977. Theories of populations in
biological communities. Springer-Verlag, New York. 144p.
Currin, B.M. 1984. Food habits and food consumption of juvenile spot,
Leiostomus xanthurus and croaker, Miaropogonias undulatus in their
nursery areas. Masters Thesis. North Carolina State University,
Raleigh. 103 p.
Currin, B.M., J.P. Reed, and J.M. Miller. 1984. Growth, production,
food consumption, and mortality of juvenile spot and croaker: a
comparison of tidal and nonti dal nursery areas. Estuaries. 7:451-
459.
Davis, G.J., H.D. Bradshaw, M.M. Brinson, and G.M. Lekson. 1985.
Salinity and nutrient dynamics in Tacks, Jacobs, and South Creeks
in North Carolina, October 1981 - November 1982. J. Elisha
Mitchell Sci. Soc. 101:37-51.
Darnell, R.M. 1958. Food habits of fishes and larger invertebrates of
Lake Ponchartrai n, Louisiana, an estuarine community. Puol.
Inst, i-lar. Sci., Univ. Texas. 5:353-416.
47
Detwyler, R. and E.H. Houde. 1970. Food selection by laboratory-reared
larvae of the scaled sardine Havengula pensacolae (Pisces:
Clupeidae) and the bay anchovy Anchoa mítchilli (Pisces:
Engraulidae). Mar. 3iol. 7:214-222.
Galat, Ü.L. and N. Vucinich. 1983. Food partitioning between young of
the year of two sympatri c tui chub norphs. Trans. Am. Fish. Soo.
112:486-497.
Gunter, G. 1961. Some relationships of estuarine organisms to salin-
ity. Lirnnot. Oaeanogr. 6:182-190.
Hobson, E.S. and J.R. Chess. 1976. Trophic interactions among fishes
and zooplankters near shore at Santa Catalina Island, California.
Fish. Bull. 74:567-598.
Hodson, R.G., J.O. Hackman, and C.R. Bennett. 1981. Food habits of
young spots in nursery areas of the Cape Fear River Estuary, North
Carolina. Trans. Am. Fish. Soc. 110:495-501.
Keast, A. 1985. Development of dietary specializations in a summer
community of juvenile fishes. Environmental Biology of Fishes.
13:211-224.
Kinch, J.C. 1979. Trophic habits of the juvenile fishes within arti -
ficial waterways—Marco Island, Florida. Univ. Texas, Mar. Sci.
Inst. 22:77-90.
Kjelson, M.A., D.S. Peters, G.W. Thayer, and G.N. Johnson. 1975. The
general feeding ecology of postlarval fishes in the Newport River
Estuary. Fish. Bull. 73:137-144.
48
Kjelson, M.A. and G.N. Johnson. 1976. Further observations of the
feeding ecology of postlarval pinfish, Lagodon rhomboides, and
spot, Leiostorms xanthuvus. Fish. Bull. 74:423-432.
Kobylinski, G.J. and P.F. Sheridan. 1979. Distribution, abundance,
feeding, and long-term fluctuations of spot, Leiostorms xanthuvus,
and croaker, Miovopogonias undulatus, in Apalachicola Bay, Florida,
1972-1977. Univ. Texas, Har. Sci. Inst. 22:149-161.
Larouche, J.L. 1982. Trophic patterns among larvae of five species of
seul pi ns (Family: Gotti dae) in a Maine estuary. Fish. Bull.
80:827-840.
Lawson, T. 1981. Nursery area assessment of Bond, Long, and Short
Creeks, Beaufort County, North Carolina. Annual report to
Texasgulf Chemicals, Inc. 134pp.
MacDonald, J.S. and R.H. Green. 1986. Food resource utilization by
five species of benthic feeding fish in Passamaquoddy Bay, New
Brunswick. Can. J. Fish. Aquat. Sai. 43:1534-1546.
Miller, J.M., J.P. Reed, and L. Pietrafesa. 1984. Patterns, mechanisms
and approaches to the study of migrations of estuarine-dependent
fish larvae and juveniles. In J.D. McCleave, G.P. Arnold, J.J.
Dodson, and W.H. Neill (eds.). Mechanisms of Migration in Fishes.
Plenum Press, New York. 554pp.
Overstreet, R.M. and R.W. Heard. 1978. Food of the Atlantic croaker,
Miovopogonias undulatus, from Mississippi Sound and the Gulf of
Mexico. Gulf Res. Re, 6:145-152.
49
Powell, A.B. and F.J. Schwartz. 1979. Food of Paralickthys dentatus
and P. lethostigrna (Pisces: Bothidae) in North Carolina estuaries.
Estuaries. 2:275-279.
Roelofs, E.W. 1954. Food studies of young Sciaenid fishes, Miaropogon
and Leiostomus from North Carolina. Copeia 1954:151-153.
Schoener, T.W. 1974. Resource partitioning in ecological
communities. Saienoe. 185:27-39.
Schwartz, F.J. 1980. Food analysis of selected fishes captured in Cape
Fear Estuary and adjacent Atlantic Ocean, North Carolina. 1973-
1973. Tech. Rpt. to Carolina Power and Light, Vol. 8: Inst, of
Mar. Sci., Uni v. of North Carolina, Morehead City, N.C.
Strauss, R.E. 1979. Reliability estimates for Ivlev's electivity
index, the forage ration, and a proposed linear index of food
selection. Trans. Am. Fish. Soo. 108:344-352.
Stickney, R.R., G.L. Taylor, and D.B. White. 1975. Food habits of five
young southeastern United States estuarine Sciaenidae. Chesapeake
Sai. 16:104-114.
Thayer, G.W., D.E. Hoss, M.A. Kjelson, W.F. Hettler, Jr. and M.W.
LaCroix. 1974. Biomass of zooplankton in the Newport River
Estuary and the influence of postlarval fishes. Chesapeake Soi.
15:9-16.
Thorman, S. 1983. Food and habitat resource partitioning between three
estuarine fish species on the Swedish west coast. Estuarine,
Coastal and Shelf Science. 17:581-692.
50
Turner, R.E. 1981. Plankton and the distribution of fishes on the
southeastern United States continental shelf. Seienae. 214:353-
354.
Weinstein, M.P. 1979. Shallow marsh habitats as primary nurseries for
fishes and shellfish. Cape Fear River, North Carolina. Fish
Bull. 77:339-357.
West, T. 1985. Abundance and diversity of benthic macrofauna in sub-
tributaries of the Pamlico River Estuary. J- Elisha Mitchell Sai,
Soa. 101:142-159.