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2012 SOUTHEASTERN NATURALIST 11(1):1–22
Prey Species of Bottlenose Dolphins (Tursiops truncatus)
from South Carolina Waters
S. Michelle Pate1,2,* and Wayne E. McFee3
Abstract - We describe the diet composition of Tursiops truncatus (Bottlenose Dolphin)
from South Carolina waters. Stomach contents of 136 dolphins stranded dead between
2000 and 2006 were examined. Eighty-two dolphin stomachs contained food items and
formed the basis for this study. The emphasis of this study was to compare the stomach
contents of dolphins that bore evidence of human interaction but were otherwise healthy
with those that appeared to die of natural causes. Forty-two prey species representing 24
families were identified. Dolphins fed predominantly on smaller-sized benthic and demersal
fish species. Diets were primarily comprised of members of the family Sciaenidae,
with Stellifer lanceolatus (Star Drum) being the most abundant species quantitatively.
Lolliguncula brevis (Brief Squid) was the most frequently observed prey item. Overall,
dolphins that appeared to have died from natural causes consumed similar species of
fish and squid to those that exhibited signs of human interaction. This study represents
the first quantitative analysis of prey species comprising the diet of Bottlenose Dolphins
found in South Carolina waters.
Defining the ecological role of marine predators such as Tursiops truncatus
Montagu (Bottlenose Dolphin) can be difficult, as their aquatic existence
often impedes direct observation of foraging behavior. Little information is
available about the dietary habits of Bottlenose Dolphins in South Carolina.
Young and Phillips (2002) developed an ecological model estimating the annual
primary production required to support a small group of dolphins in a
salt marsh creek ecosystem. Recks’ (2004) study of dietary history using blubber
fatty-acid profiles from live free-ranging dolphins provide broad indices
of food habits for Bottlenose Dolphins in the near-shore and estuarine waters
Dietary studies on marine mammals traditionally have used dead stranded
animals, but this might not accurately depict the dietary habits of healthy living
populations because the possibility of poor health prior to stranding could
bias the analysis (Selzer et al. 1986). If an animal was ill prior to stranding, it
may have been unable to obtain food or fed on prey or prey sizes that do not
represent normal foraging behavior. Stomach contents of animals that died an
acute or sudden death (i.e., human-interaction cases) may be considered a better
1College of Charleston, 66 George Street, Charleston, SC 29424. 2Current address -
South Carolina Department of Natural Resources, Marine Resources Research Institute,
217 Fort Johnson Road, Charleston, SC 29412. 3National Oceanic and Atmospheric
Administration, National Ocean Service, Center for Coastal Environmental Health and
Biomolecular Research, 219 Fort Johnson Road, Charleston, SC 29412. Corresponding
author - PateS@dnr.sc.gov.
2 Southeastern Naturalist Vol. 11, No. 1
indicator of a “normal diet”. Although debate remains over the validity of using
diet information from dead stranded animals, comparing dead stranded animals
with animals known to have died from interactions with humans (e.g., fishery
entanglements, boat strikes) could provide some insight into this problem.
This study provides data on the feeding habits of Bottlenose Dolphins off
the coast of South Carolina (Fig. 1) as determined through stomach content
analysis. Accordingly, there were three primary objectives: 1) to quantitatively
describe the diet of stranded Bottlenose Dolphins; 2) to determine if
prey items consumed differed according to sex, age, and season, and between
stranding locations; and 3) to determine if any significant differences existed
in the dietary composition of dolphins that died from human interaction and
dolphins that did not.
Bottlenose Dolphins that stranded dead in the estuarine and nearshore
(ocean) waters of South Carolina were inspected for signs of human
interaction and classified into one of three categories: Non-human interaction
(Non-HI), human interaction (HI), and cannot be determined (CBD). Dolphin
death attributed to illness, disease, or natural causes were classified as
Non-HI. Dolphin deaths due to fishery activities and boat strikes, or stranded
dolphins exhibiting other signs (e.g., rope wounds, mutilation) associated with
human activities were classified as HI (Geraci and Lounsbury 2005, Read
Figure 1. Map of South Carolina coastline showing locations of non-human interaction
and human interaction Bottlenose Dolphin strandings.
2012 S.M. Pate and W.E. McFee 3
and Murray 2000). Evidence of human interaction for dolphins in this study
included: mutilation, parallel lacerations from boat propellers, presence of
fishing gear (i.e., ingested or entangled), and marks suggestive of entanglement
from other fishery interactions.
Dolphin specimens were measured for total body length (taken from the tip of
the upper jaw to the fluke notch; Hoffman 1991), and sex was determined when
possible. Dolphins were also grouped as mature or immature. Maturity was determined
via length, tooth aging, and/or the development of reproductive organs
(Perrin and Reilly 1984). Male dolphins greater than 240 cm and female dolphins
greater than 220 cm (Odell 1975) were considered sexually mature if gonads
were not examined.
Whole stomachs (including forestomach, main, and pyloric chambers) were
removed (in the field or in the laboratory), tied off at the esophageal and pyloric
ends, placed in a labeled bag, and frozen at -20 °C pending further analysis.
Each dolphin stomach was weighed (g) and whole, intact undigested prey items
removed for identification and measurement. Remaining stomach contents were
washed through a 1-mm sieve and hand sorted. The wet weight of the stomach
contents was estimated by subtracting the weight of the empty stomach from the
initial weight of the stomach with contents.
Loose fish otoliths were stored dry. Identification of otoliths and fish bones
was made using local reference collections and with assistance from the South
Carolina Department of Natural Resources (SCDNR) Inshore Fisheries group
(Charleston, SC). Published identification keys and pictorial guides were also
used (Baremore and Bethea 2010, Campana 2004, Chao 1978, Gregory 1959,
Mohsin 1981). Determination of left or right otoliths was based on the orientation
of the sulcus acousticus. The number of intact fish, plus the greater number
of either left or right sagittae indicated the minimum number of individual prey
species present. When digestion of the sulcus prevented separation into either left
or right sagittae, the total number of fish present was estimated by taking half the
number of otoliths. Otoliths that were heavily digested or broken were classified
as unidentified. Cephalopod beaks were stored in 70% ethanol and identified according
to Clarke (1986) with the aid of a local reference collection. These were
separated into upper and lower mandibles, and the greater count of either provided
the estimated minimum number of individuals consumed. Counts of either
shrimp rostra or telsons indicated the numbers of shrimp present. All prey items
were identified to the lowest possible taxon.
Relative importance of individual prey items to total diet of each dolphin was
determined using percent composition by number (%N) and percent frequency of
occurrence (%F). These measures were also determined for stomachs grouped by
sex, age, season, stranding location (ocean and estuarine) and stranding category
(HI and Non-HI). Species richness (D) (the number of species per stomach) and
4 Southeastern Naturalist Vol. 11, No. 1
species diversity (H) using the Shannon Index (Krebs 1999) were also determined
for dolphins classified as HI or Non-HI.
Variation in the composition of prey items was evaluated according to sex,
age, and season and between ocean and estuarine stranding locations. A comparison
of diet composition between HI and Non-HI dolphins was made to assess
the validity of using stranded dolphins to determine dietary habits of healthy
dolphins. Hydrographic seasons were defined as: winter (December–February),
spring (March–May), summer (June–August), and fall (September–November).
Non-parametric tests were used after rejecting the hypothesis of normality
(Shapiro-Wilk test). All statistical analyses were conducted using JMP®
statistical software (version 184.108.40.206; SAS Institute, Cary, NC). To determine
the significance of diet variation between HI and Non-HI dolphins, a Mann-
Whitney U (MWU) test was used to compare means for number of prey items
(abundance), species richness, and wet weight of stomach contents. Contingency
table analysis was used to compare observed frequencies of prey type
(fish, squid, and shrimp) between Non-HI and HI dolphins and of specific
prey species (≥2% composition by number) by dolphin sex and location between
Non-HI and HI dolphins. To reconstruct prey measurements (length and
weight) of species recovered from dolphin stomachs, linear regression equations
of otolith lengths were derived from total length measurements of fresh
prey specimens collected in Charleston, SC (Table 1). Measurements of excessively
eroded or broken otoliths recovered from stomach contents were not
included in the prey-size regression.
Variation in the diet between male and female dolphins, between mature
and immature dolphins, and between stranding locations for the total dolphin
sample (HI and Non-HI combined) was examined using a Mann-Whitney
U test comparing means for abundance, species richness, and wet weight of
stomach contents. Differences in the abundance of prey species among seasons
were investigated using a Kruskal-Wallis test. All results were significant
at alpha level P > 0.05.
Table 1. Regression equations relating otolith length (OL) to total length (TL) of fish and beak
length (BL) to squid mantle length (ML) for six important species in the diet of Bottlenose Dolphins
from South Carolina.
Prey Items n Regression equation R2 (mm) (g)
Stellifer lanceolatus 19 TL = 50.12 + 21.55 (OL) 0.780 109–128 12–28
Anchoa mitchilliA 16 SL = 12.1 + 21.4 (OL) 0.930 41–60 1–4
Leiostomus xanthurus 15 TL = -48.64 + 42.44 (OL) 0.996 46–220 2–141
Bairdiella chrysoura 16 TL = -4.2 + 37.15 (OL) 0.985 43–138 1–36
Micropogonius undulatus 29 TL = 8.85 + 27.44 (OL) 0.932 84–244 5–171
Lolliguncula brevis 11 ML = 11.07 + 48.03 (BL) 0.706 36–65 4–20
ARegression equation from Barros (1993), standard length (SL).
2012 S.M. Pate and W.E. McFee 5
Total dolphin sample composition
Homogeneity in the dolphin sample was investigated using chi-square
analysis for age, sex, and location variables. No significant differences were
found when comparing the frequencies of prey types consumed; therefore, the
pooling of data into groups based on age, sex, and location was considered
appropriate as these variables should not introduce any bias (age: χ2 = 1.444,
df = 2, P = 0.486; sex: χ2 = 4.667, df = 3, P = 0.198; location: χ2 = 5.033, df =
4, P = 0.284).
Stomachs from 136 Bottlenose Dolphins collected between 2000 and 2006
were evaluated. One adult dolphin, determined to be of offshore ecotype based
on genetic analysis and skull meristics (Hersh and Duffield 1990, Hoelzel et al.
1998, Mead and Potter 1995), and two adult specimens not sexed due to decomposition
were excluded from analysis. Thirty neonate and 21 juvenile or adult
dolphins (equivalent to 12% of HI and 23% of non-HI dolphins), whose stomachs
contained only milk or were empty, were also excluded. The remaining 82 dolphin
stomachs that contained food items (37 immature and 45 mature, 35 females
and 47 males) were used to determine the relative importance of prey species
consumed by Bottlenose Dolphins in South Carolina.
Diet composition for stomachs containing food items
The 82 dolphins whose stomachs contained evidence of food items were a
mixture of HI and non-HI dolphins from ocean and estuarine regions. They fed
predominantly on fish, which occurred in 90% (n = 74) of the stomachs examined.
Squid alone was present in 10% of the dolphins (n = 8). The number of
individual prey taxa found in individual stomachs ranged from 1 to 14, with a
majority of the stomachs (77%) containing more than one type of prey species
(mean = 4.90). Loose otoliths and cephalopod beaks recovered from the stomach
contents numbered 14,852 and 141, respectively. The 82 dolphins fed on a
minimum of 7851 individual prey items and a minimum of 42 different identified
species of prey representing 24 different families (Tables 2, 3). Two-hundred
twenty-six (226) otoliths and two cephalopod beaks were not identified, which
could represent additional prey species consumed by dolphins in this study. Overall,
important prey species in terms of abundance included Stellifer lanceolatus
(Star Drum), Lolliguncula brevis (Brief Squid), Anchoa mitchilli (Bay Anchovy),
and Leiostomus xanthurus (Spot). Brief Squid, contained in over half the stomachs
(n = 47), were consumed most often. Prey species of the Sciaenidae family
occurred in 76% of stomachs and represented 61% of prey items consumed.
Dolphins consumed fishes ranging from 17 mm total length (TL) to 337 mm
TL, as well as a 910-mm Mustelus canis (Smooth Dogfish; length estimated).
The smallest fish species identified was Bay Anchovy with a mean TL of 44 mm.
Mean TL of Star Drum, Bairdiella chrysoura (Silver Perch), Spot, and Micropogonius
undulatus (Atlantic Croaker) consumed were 113 mm, 137 mm, 142 mm,
and 210 mm, respectively. Brief Squid ranged in size from 17 to 65 mm mantle
length (mean = 64).
6 Southeastern Naturalist Vol. 11, No. 1
Table 2. Percent composition by number (N) and percent frequency of occurrence (F) for prey items
identified in the stomach contents of all Bottlenose Dolphins (n = 82), immature and mature male and
female dolphins, and dolphins stranding in oceanic and estuarine waters of South Carolina between
2000 and 2006. The less than sign (<) denotes prey items less than 1% in numerical abundance. O =
oceanic, E = estuarine. Common names and authorities for all species listed given in Table 3.
All Immature Mature
dolphins Females Males Females Males O E
(n = 82) (n = 16) (n = 21) (n = 17) (n = 23) (n = 48) (n = 34)
Prey items N F N F N F N F N F N F N F
Stellifer lanceolatus 40 44 56 38 19 48 36 35 30 43 22 32 54 29
Leiostomus xanthurus 10 37 6 50 3 24 12 29 23 30 19 26 2 26
Micropogonius undulatus 3 35 1 31 3 33 1 24 10 48 7 26 1 24
Bairdiella chrysoura 4 27 < 38 6 24 1 24 11 22 5 16 3 26
Cynoscion nothus 1 22 1 44 1 10 1 18 1 17 1 12 1 24
Larimus fasciatus 1 17 1 31 1 14 2 12 < 9 1 13 < 9
Cynoscion regalis 1 16 < 13 < 5 5 24 1 17 2 13 < 9
Menticirrhus americanus 1 10 1 13 < 5 < 12 1 13 1 7 < 6
Cynoscion spp. < 10 < 13 < 10 1 13 < 6 < 9
Menticirrhus spp. < 6 < 9 < 4 < 6
Cynoscion nebulosus < 6 < 6 < 5 < 6 < 9 < 1 < 9
Sciaenops ocellatus < 2 < 6 < 4 < 2 < 3
Pogonias cromis < 1 < 4 < 1
Sciaenid sp. < 1 3 6 < 1
Brevoortia tyrannus 2 26 2 44 1 33 < 6 < 13 4 16 1 24
Anchoa mitchilli 11 21 9 31 33 24 1 18 1 13 11 15 11 15
Anchoa hepsetus 4 16 < 31 13 24 < 12 3 4 4 11 3 12
Cusk eel spp. 1 12 1 13 < 14 3 17 0 7 1 12
Mugil cephalus < 12 < 25 < 5 < 6 < 13 0 6 < 15
Prionotus sp. 1 9 1 13 < 10 1 13 0 5 1 9
Lagodon rhomboides < 7 < 13 1 6 2 13 1 5 < 6
Orthopristis chrysoptera < 6 < 13 < 5 < 9 < 4 < 6
Urophycis sp. < 6 < 5 < 12 < 9 < 2 < 9
Trichiurus lepiturus < 6 < 25 < 4 < 5 < 3
Paralichthys dentatus < 7 < 13 < 5 < 9 < 4 < 9
Paralichthys lethostigma < 2 < 4 < 2
Paralichthys sp. < 1 < 1
Opsanus tau 2 12 2 19 4 10 < 6 < 17 < 4 3 21
Porichthys plectrodon < 4 < 6 < 5 < 4 < 4
2012 S.M. Pate and W.E. McFee 7
There were 131 undigested fish representing ten species recovered from the
stomachs of thirteen dolphins. The fish recovered included Brevoortia tyrannus
(Atlantic Menhaden), Peprilus triacanthus (Butterfish), Menticirrhus spp., Paralichthys
dentatus (Summer Flounder), Spot, Porichthys plectrodon (Atlantic
Midshipman), Atlantic Croaker, Opsanus tau (Oyster Toadfish), Menticirrhus
americanus (Southern Kingfish), and Mugil cephalus (Striped Mullet). The largest
proportion of whole fish remains recovered ranged from 80–119 mm TL. The
largest undigested teleost fish was an Oyster Toadfish at 291 mm TL, followed
Table 2, continued.
All Immature Mature
dolphins Females Males Females Males O E
(n = 82) (n = 16) (n = 21) (n = 17) (n = 23) (n = 48) (n = 34)
Prey items N F N F N F N F N F N F N F
Synodus foetens < 5 < 6 1 6 1 4 1 4 < 3
Anguilla rostrata < 5 2 10 < 6 < 4 < 4 < 3
Myrophis punctatus < 1 < 6 < 1
Ophichthus gomesi < 1 < 5
Elops saurus < 2 < 6 < 4 < 2
Centropristis striata < 1 < 6
Centropristis philadelphica < 1 < 6
Peprilus triacanthus < 1 < 1
Catfish sp. < 1 < 4 < 1
Selene setapinnis < 1 < 6
Hypsoblennius hentzi < 1 < 6
Unidentified fish spp. 3 45 1 50 3 43 < 24 7 52 4 29 2 38
Mustelus canis < 1 < 1
Lolliguncula brevis 13 56 15 75 6 43 32 59 5 52 9 33 16 56
Unidentified squid sp. < 1 < 6 < 3
Litopenaeus setiferus 1 16 1 25 2 14 < 12 < 9 2 12 1 9
Penaeus aztecus < 2 < 13 < 6
Unidentified shrimp sp. < 7 < 10 < 18 < 4 < 4 < 9
Portunus sayi < 1 < 1
8 Southeastern Naturalist Vol. 11, No. 1
Table 3. Scientific names with authorities and common names for fish species identified as prey items in the stomachs of Bottlenose Dolphins examined in
Prey items Common name Prey items Common name
Bony fishes Porichthys plectrodon Jordan & Gilbert Atlantic Midshipman
Stellifer lanceolatus Holbrook Star Drum Synodus foetens L. Inshore Lizardfish
Leiostomus xanthurus Lacepède Spot Stromateidae
Micropogonius undulatus L. Atlantic Croaker Peprilus triacanthus Peck Atlantic Butterfish
Bairdiella chrysoura Lacepède Silver Perch Anguillidae
Cynoscion nothus Holbrook Silver Seatrout Anguilla rostrata Lesueur American Eel
Larimus fasciatus Holbrook Banded Drum Ophichthidae
Cynoscion regalis Bloch & Schneider Weakfish Myrophis punctatus Lütken Speckled Worm Eel
Menticirrhus americanus L. Southern Kingfish Ophichthus gomesi Castelnau Shrimp Eel
Cynoscion nebulosus Cuvier Spotted Seatrout Elopidae
Sciaenops ocellatus L. Red Drum Elops saurus L. Ladyfish
Pogonias cromis L. Black Drum Serranidae
Clupeidae Centropristis striata L. Black Sea Bass
Brevoortia tyrannus Latrobe Atlantic Menhaden Centropristis philadelphica L. Rock Sea Bass
Anchoa mitchilli Valenciennes Bay Anchovy Selene setapinnis Mitchill Moonfish
Anchoa hepsetus L. Striped Anchovy Blenniidae
Mugilidae Hypsoblennius hentzi Lesueur Feather Blenny
Mugil cephalus L. Striped Mullet Cartilaginous fish
Lagodon rhomboides L. Pinfish Mustelus canis Mitchill Smooth Dogfish
Orthopristis chrysoptera L. Pigfish Lolliginidae
Trichiuridae Lolliguncula brevis Blainville Brief Squid
Trichiurus lepiturus L. Cutlassfish Crustaceans
Paralichthys dentatus L. Summer Flounder Litopenaeus setiferus L. Northern White Shrimp
Paralichthys lethostigma Jordan & Gilbert Southern Flounder Penaeus aztecus Ives Northern Brown Shrimp
Opsanus tau L. Oyster Toadfish Portunus sayi Gibbs Sargassum Crab
2012 S.M. Pate and W.E. McFee 9
by a Southern Kingfish at 227 mm TL. Eighty-five (64.9%) of the 131 whole fish
recovered from the stomachs were Atlantic Menhaden.
Non-HI and HI dolphin diet comparison
Fifteen dolphins were categorized as HI for this analysis: five stranded in the
oceanic region and ten within the estuarine region. Of the remaining sixty-seven
dolphins that had food items present in their stomachs, the cause of death for
five dolphin carcasses could not be deemed direct results of observed human
interaction and were classified as CBD. Therefore, 62 dolphins containing food
items were considered non-HI: 39 stranded in the oceanic region and 23 in the
estuarine region. The smaller HI sample size prevented examination by season
and age; therefore, evaluation of differences in prey items was restricted to sex
and stranding location.
Although the differences were not found to be statistically significant
(Z = 1.872, P = 0.061), mean number of items consumed by HI dolphins was
86 (range: 2–389) whereas Non-HI dolphins consumed an average of 68 items
(range: 1–473). HI dolphins on average consumed a more diverse diet, with an
average of 6.20 ± 4.35 SD different prey taxa per stomach compared to 4.47 ±
3.74 SD for Non-HI dolphins (Z = 1.366, P = 0.172). The mean stomach wet
weight among HI dolphins was 555 g, with a range of 18–2430 g, and for non-HI
dolphins the mean was 278 g, with a range of 0–2970 g (Z = 1.427, P = 0.154).
Richness (D) was 1.03 for HI dolphin species, and 0.60 for non-HI species. Species
diversity (H) was 2.25 for HI dolphins and 2.46 for non-HI dolphins.
The prey composition of the stomach contents was analyzed according to
how frequently each prey type (fish, shrimp, and squid) or any combination of
the three occurred. Fish alone or in combination with other prey types accounted
for 90% of the samples in non-HI dolphins and 87% of samples in HI dolphins.
Shrimp alone was never observed in any specimens, and squid alone occurred in
10% and 13% of the non-HI and HI samples, respectively. The stomach contents
of non-HI dolphins revealed a predominance of fish alone, but no significant
difference was found between HI and non-HI dolphins for the frequency of occurrence
of fish (χ2 [n = 77] = 0.173, P = 0.677) or squid (χ2 [n = 77] = 1.104,
P = 0.293). However, shrimp was found to occur more significantly in the HI
dolphins (χ2 [n = 77] = 4.149, P < 0.042).
Non-HI female dolphins consumed ten different species, while HI females
consumed individuals from 5 different species (Table 4). Brief Squid, accounting
for half the diet composition by number, dominated the diet of HI female
dolphins. HI female dolphins also consumed Star Drum, Atlantic Menhaden,
Cynoscion nothus (Silver Seatrout), and Spot to a lesser extent. Despite the
abundance of a single species in the diet of HI females, there were no significant
differences in the frequency of occurrence for the ten species evaluated between
non-HI and HI females (contingency table analysis, P > 0.05).
Non-HI males consumed eight prey species (≥2% by number), while HI male
dolphins consumed nine species. Bay Anchovy and Oyster Toadfish were consumed
significantly more often by HI male dolphins (χ2 [n = 44] = 5.246, P <
0.022; χ2 [n = 44] = 4.728, P < 0.030).
10 Southeastern Naturalist Vol. 11, No. 1
Table 4. The percent composition by number (N) and percent frequency of occurrence (F) for prey items recovered from the stomach contents of non-human
interaction (non-HI) and human interaction (HI) Bottlenose Dolphins stranded in waters of South Carolina collected between 2000 and 2006. Less than sign (<)
denotes prey item less than 1% composition by number. Prey items measuring less than 2% composition by number for all categories not presented in table.
Non-HI HI Oceanic Estuarine
Male Female Male Female Non-HI HI Non-HI HI
(n = 36) (n = 26) (n = 8) (n = 7) (n = 39) (n = 5) (n = 23) (n = 10)
Prey Items N F N F N F N F N F N F N F N F
Stellifer lanceolatus 21 42 21 38 32 63 20 29 23 54 31 40 15 17 29 50
Leiostomus xanthurus 15 28 16 42 10 63 2 14 20 44 18 40 3 22 6 40
Micropogonius undulatus 9 42 3 31 1 25 0 14 8 49 0 0 2 17 1 30
Bairdiella chrysoura 7 19 1 31 10 38 1 29 6 31 0 0 1 13 9 50
Cynoscion nothus 1 14 1 27 1 38 3 29 1 23 0 0 1 13 1 50
Larimus fasciatus 1 14 2 19 0 25 0 0 1 21 1 40 2 9 0 0
Cynoscion regalis 1 17 2 23 0 13 0 0 2 23 3 20 < 13 0 0
Menticirrhus americanus 1 8 2 12 0 25 0 0 2 13 < 20 < 4 < 10
Unidentified Sciaenidae 0 0 2 4 0 0 0 0 1 3 0 0 0 0 0 0
Brevoortia tyrannus 3 25 3 19 2 50 9 14 4 26 8 40 1 17 3 30
Anchoa mitchilli 16 14 1 27 17 50 0 0 13 28 1 20 < 4 16 30
Anchoa hepsetus 12 14 1 15 0 13 0 14 5 18 < 20 12 9 < 10
Cusk eel spp. < 11 1 8 5 38 0 0 < 10 2 20 2 9 4 20
2012 S.M. Pate and W.E. McFee 11
Table 4, continued. T
Non-HI HI Oceanic Estuarine
Male Female Male Female Non-HI HI Non-HI HI
(n = 36) (n = 26) (n = 8) (n = 7) (n = 39) (n = 5) (n = 23) (n = 10)
Prey Items N F N F N F N F N F N F N F N F
Prionotus spp. < 8 2 4 0 13 0 0 < 8 0 0 3 4 < 10
Opsanus tau < 8 4 12 7 38 1 14 1 8 0 0 6 13 6 40
Synodus foetens < 3 < 4 1 13 0 14 1 5 3 20 0 0 < 10
Unidentified fish spp. 4 50 3 35 6 75 1 43 4 51 2 60 1 35 6 60
Lolliguncula brevis 7 47 34 62 2 63 58 71 8 56 15 60 48 48 13 70
Litopenaeus setiferus 1 11 1 15 4 38 0 14 1 21 11 40 1 0 1 20
12 Southeastern Naturalist Vol. 11, No. 1
The percent composition by number and percent frequency of prey items
recovered from Non-HI and HI dolphins that stranded in both the oceanic and
estuarine regions of South Carolina are listed in Table 4. Non-HI dolphins
stranding in the oceanic region consumed prey (>2% by number) belonging to
10 species: Star Drum, Spot, Bay Anchovy, Brief Squid, Silver Perch, Atlantic
Croaker, Atlantic Menhaden, Anchoa hepsetus (Striped Anchovy), Cynoscion
regalis (Weakfish), and Southern Kingfish. HI dolphins also consumed Star
Drum, Spot, Brief Squid, shrimp, Atlantic Menhaden, Synodus foetens (Inshore
Lizardfish), Weakfish, and Ophidiidae spp. (cusk eels).
The diet of both non-HI and HI dolphins stranding in the estuarine region
included Star Drum, Bay Anchovy, Spot, and Brief Squid among others. Brief
Squid dominated the diet for non-HI dolphins in number at 48%, yet the observed
frequency of occurrence of squid between HI and non-HI dolphins was
not statistically significant (χ2 [n = 33] = 1.382, P > 0.240). Silver Perch and
Bay Anchovy occurred significantly more frequently in the diet of HI dolphins
stranded in the estuarine region (χ2 [n = 33] = 5.183, P < 0.023; χ2 [n = 33] =
4.306, P < 0.038).
Differences in diet according to dolphin sex and maturity for overall sample
Combining the HI and non-HI dolphins specimens together allowed comparisons
in diet to be made for the overall sample (n = 82) between dolphin sex and
maturity. Female dolphins consumed a greater diversity of prey taxa (mean =
5.14 ± 4.1) than males (mean = 4.74 ± 3.9) and a greater abundance of prey items
(mean = 124 ± 375) than males (mean = 74 ± 115). The average stomach content
wet weight was 368 g for females and 356 g for males. However, the differences
between the averages for taxa, prey items, and wet weight between males and
females were not statistically significant (taxa: Z = 0.464, P = 0.643; prey items:
Z = 0.525, P = 0.599; wet weight: Z = 0.217, P = 0.828).
Among maturity stages, sexually mature and immature males consumed
nearly the same average number of prey items (means = 75 and 74, respectively).
Sexually immature females consumed an average of 220 prey items, and
mature females consumed an average of 44 items. The diet of immature female
dolphins was dominated in number by Star Drum (56%). However, Brief Squid
was observed most frequently at 75%, with Star Drum only occurring in 38% of
the samples. There were no significant differences in the averages evaluated for
taxa, prey items, and wet weight between immature and mature dolphins (taxa:
Z = 0.541, P = 0.588; prey items: Z = 0.420, P = 0.675; wet weight: Z = 0.022,
P = 0.951).
The diet composition by number and percent frequency of occurrence for
select prey species consumed by immature and mature male and female Bottlenose
Dolphins are listed in Table 2. Over half of the prey items consumed
by mature females in number consisted of Star Drum (36%) and Brief Squid
(32%). Star Drum (56%) was the most consumed prey item in number for the
immature females’ diet. The diet of mature males was composed, by number,
of eight different prey species (87%), whereas immature males contained ten
2012 S.M. Pate and W.E. McFee 13
(89%). Mature males consumed Star Drum, Spot, Silver Perch, and Atlantic
Croaker. Immature males consumed Bay Anchovy, Star Drum, and Striped Anchovy.
Brief Squid was the most frequently observed prey item for all sex and
maturity classes with the exception of immature males. In immature males, Star
Drum was observed most often.
Differences in diet according to stranding location for overall sample
The diet composition by number of dolphins stranded in the oceanic region
primarily consisted of Star Drum (22%), Spot (19%), and Bay Anchovy (11%).
Dolphins in this region consumed an average of 45 prey items, consisting of an
average of 5.40 ± 3.7 prey taxa, with a mean wet weight of 424 grams.
More than half of the estuarine dolphin diet composition consisted of Star
Drum (54%), followed by Brief Squid (16%). Estuarine dolphins consumed an
average of 128 prey items, consisting of an average of 4.21 ± 4.2 prey taxa with
a mean wet weight of 293 grams. Brief Squid was the most frequently observed
prey item in both the oceanic (56%) and estuarine regions (33%) (Table 2).
Seasonal differences in diet
Nineteen Bottlenose Dolphins stranded during winter, 17 during spring, and
23 dolphins each during the summer and fall. Star Drum was observed in stomachs
in all four seasons, but was most abundant during winter and least abundant
during summer (Fig. 2). Brief Squid was the most abundant prey in the spring and
was observed most frequently in every season except winter. Bay Anchovies were
consumed in every season except spring. Spot was consumed in every season
except winter and was the only species significantly abundant in the dolphin diet
(Kruskal-Wallis, Fall: H = 9.51, P > 0.023). Atlantic Croaker, Striped Anchovy,
and Atlantic Menhaden were only consumed in the summer and fall. More species
were observed or consumed during fall (n = 11) than winter (n = 4), with
spring and summer having intermediate abundances.
Human interaction dolphins
The inherent problems with the use of stomach content analysis for determining
dietary habits have been reviewed in various papers (Jobling and
Breiby 1986, Pierce and Boyle 1991) and researchers suggest that the stomach
contents of dolphins exhibiting signs of human interaction would better
represent the diet of healthy individuals. Previous studies on Bottlenose dolphin
stomach contents throughout the southeastern United States found no
qualitative differences in the diet of stranded dolphins that died as a result of
natural and anthropogenic causes (Barros 1993, Barros and Odell 1990, Mead
and Potter 1990). An objective of this study was to assess the validity of using
stranded dolphins to determine the dietary habits of dolphins through a
statistical comparison of the diets of dolphins whose deaths were not of anthropogenic
origin (presumed diseased) and dolphins that died as a result of
human interaction (presumed healthy based on histopathology results).
14 Southeastern Naturalist Vol. 11, No. 1
Results of the evaluation between the non-HI and HI Bottlenose Dolphins in
the waters of South Carolina indicated that both groups of dolphins consume a
similar diet of fish, cephalopods, and crustaceans. These results are consistent
with previous analysis of stomach contents of Bottlenose Dolphins in the southeastern
United States. However, shrimp occurred significantly more often in
the HI group, indicating those dolphins could be incidentally ingesting shrimp
more often than non-HI dolphins while targeting by-catch species and prey items
stirred up during the trawling process.
Overall dietary habits of dolphins in South Carolina
Bottlenose Dolphins stranded in South Carolina waters were primarily piscivorous,
consuming a variety of smaller-sized benthic and demersal coastal
inshore fish species. The most abundant family of fish consumed in this study
was the Sciaenidae, typically found in estuaries, in muddy bays, and near
shallow banks. Star Drum numerically dominated the dietary composition of
dolphin stomach contents. This small bottom-dwelling fish is the most abundant
marine fish in the coastal waters of South Carolina (Bearden 1964), and
the mean size consumed by dolphins in this study was 113 mm, equivalent to
a juvenile or one-year-old fish of this species (Shealy et al. 1974). Star Drum
typically spawns in the late spring and early summer, with a peak spawning
Figure 2. Important prey items in terms of percent composition by number (for species
greater than 2%) recovered from the stomach contents of stranded Bottlenose Dolphins in
South Carolina according to season. All prey species representing less than 2% composition
by number were grouped collectively in the “other” category.
2012 S.M. Pate and W.E. McFee 15
period in July (Shealy et al. 1974). Unlike many fish species, Star Drum appear
to exhibit no spawning migration, as both juveniles and adult fish are
present in estuaries during the spawning season (Shealy et al. 1974). In this
study, Star Drum was consumed throughout the year in varying quantities,
reflecting the seasonal abundance, prey availability, and seasonal pattern in
sound production. The distribution of Star Drum along the Atlantic coastline
varies, but they most often occur from North Carolina to Northeast Florida,
which may explain why this species is not consumed to a greater extent by
dolphins further south or in the Gulf States.
Bottlenose Dolphins are diverse in their consumption of various species (42
different species consumed in this study alone) yet preferences were apparent. Sciaenids,
which dolphins in this study consumed abundantly, are highly soniferous
(Ramcharitar et al. 2006) and are prevalent in the nearshore waters off the south
Atlantic coast (SCDNR SEAMAP 2000). Additional soniferous fishes consumed
to a lesser extent by dolphins in this study included members of the family Batrachoididae
(Oyster Toadfish and Atlantic Midshipman; Fish and Mowbray 1970,
Gray and Winn 1961) and Ophidiidae (cusk eels; Mann et al. 1997, Sprague and
Luczkovich 2001). Previous stomach content studies in the southeastern United
States (Barros 1993, Barros and Odell 1990, Gannon 2003, Gannon and Waples
2004) demonstrated that soniferous fishes, especially Sciaenids, also dominated
the dolphins’ diet. However, dolphins did not appear to consume soniferous fish at
those times when they would be most actively producing sounds (i.e., spawning).
Gannon (2003) also found this to be true, and suggested that members of the family
Sciaenidae might produce vocalizations not associated with spawning, but nevertheless
detectable by dolphins (Gannon and Waples 2004). Barros and Odell (1990)
first theorized that Bottlenose Dolphins employ passive listening while foraging to
explain the consumption of sound-producing fish. Gannon et al. (2005) later tested
this theory, providing experimental evidence that dolphins responded to recorded
calls of prey fish, changing their travel direction and rate of echolocation to orient
themselves toward the source of the sounds and Gannon and Taylor (2007)
documented that Atlantic Croaker produced sound outside of the spawning season.
Berens McCabe et al. (2010) found wild resident Bottlenose Dolphins occupying
an inshore coastal habitat selected for soniferous prey, lending further support to
the passive-listening foraging hypothesis. Dolphins in the present study occupied
both coastal inshore and open coastal habitats which likely require the use of multiple
foraging techniques including passive listening and would account for the
variety of fish species consumed overall.
Striped Mullet has long been considered a common prey item for Bottlenose
Dolphins (Barros and Odell 1990, Barros and Wells 1998, Caldwell and
Caldwell 1972, Gunter 1942, Shane 1990), and the near absence of this species
in the dolphin samples was notable. Mullet are commonly found in coastal
inshore waters year round, but spawn offshore and can tolerate a wide salinity
range in South Carolina (McDonough et al. 2003). Dolphins have been observed
capturing mullet while “strand feeding” on intertidal creek banks in
South Carolina (Petricig 1995, Zolman 1996). Mullet jump out of water when
16 Southeastern Naturalist Vol. 11, No. 1
chased by predators, and this increased visibility may lead observers to overestimate
the amount of mullet actually fed on by dolphins (Barros and Odell
1990). Berens McCabe et al. (2010) also found no quantitative evidence for the
hypothesis that Bottlenose Dolphins select for Striped Mullet. Blubber fatty
acid analysis on living dolphin populations in South Carolina (Recks 2004)
found evidence that mullet were consumed, but dolphins occupying the North
Edisto River (just South of Charleston, SC) specifically appeared to consume
more mullet than dolphins of other Charleston waters. Recks (2004) conceded
that the unique signature of mullet that contributes to its ease of detection in
fatty acid analysis could cause it to be overestimated in its importance to the
dolphin diet. However, results from the present study showed that Striped
Mullet contributed a very small amount (less than 1%) to the diet of dolphins in South
Carolina. Mead and Potter (1990) found no evidence of mullet in Bottlenose
Dolphins stranded in North Carolina, Virginia, and Maryland, and less than 1%
was observed in stomachs analyzed by Gannon (2003) from North Carolina.
Results from the Indian River Lagoon in Florida indicated a small number of
mullet consumed by dolphins there (Barros 1993).
Sex and maturity
Results of the present study on Bottlenose Dolphins indicated there was a
dietary difference by sex and maturity. The diet of immature males showed
a dominance of schooling fish species, with almost half of prey items consisting
of anchovies. This targeting of schooling fish may be the response of inexperienced
hunters attracted to prey items that may be easier to catch. These large
numbers of anchovies present could be secondary ingestion from another fish
species consumed; however, we would anticipate seeing large numbers of otoliths
from higher trophic level fish also present in the stomach.
Brief Squid was the most frequent prey species of all dolphins with the exception
of immature males. Although differences were not significant, there
appeared to be a trend for female dolphins to consume Brief Squid, especially
among reproductively mature females. Gannon (2003) found similar results with
mature female Bottlenose Dolphins in North Carolina. Female Stenella attenuata
(Gray) (Pantropical Spotted Dolphin) also consumed more squid in a study by
Robertson and Chivers (1997). Cockcroft and Ross (1990) found lactating Bottlenose
Dolphins consumed more cephalopods than non-lactating females. Bernard
and Hohn (1989) found female Spotted Dolphins consumed more fish during
lactation, while pregnant females consumed more squid. The authors conceded
that dietary results for lactating females might not be the norm, referencing a
larger sample of Spotted Dolphins from the same area whose dominant food item
was squid. Females could be consuming squid because of higher caloric content
required for reproduction or lactation or because of habitat preferences. Additionally,
the optimal foraging theory (MacArthur and Pianka 1966) predicts that
an animal will behave in a way that maximizes its caloric intake while minimizing
its effort including behavior such as avoidance of predators. The increased
energetic requirements dictate that these animals will meet the caloric demands
2012 S.M. Pate and W.E. McFee 17
by consuming more of their normal prey while supplementing their diet with the
next best species available. Without more information on the caloric value of
squid as compared to fish species, it is difficult to interpret the consumption trend
of squid by female dolphins in this study.
Dietary differences among the oceanic and estuarine dolphins appeared to
reflect different prey availability in the habitats they occupy. Residence patterns
have been established for Bottlenose Dolphins occupying a least one estuarine
area in South Carolina (Zolman 2002). Distribution patterns and diet composition
of Bottlenose Dolphins in estuarine areas suggest that dolphins forage on the
most prevalent teleost fish species occurring in the habitat they routinely occupy,
such as Star Drum.
The prey composition of the oceanic region was compared with results
of the dietary studies on Bottlenose Dolphins that inhabited similar habitat
along the coast of North Carolina (Gannon and Waples 2004) in an effort to
assist with the stock differentiation of Bottlenose Dolphins occupying nearshore
South Carolina waters. The diet composition of dolphins that stranded
in the oceanic region of this study was comprised mainly of Atlantic Croaker,
Spot, and Striped Anchovy. Bottlenose Dolphins stranded on ocean beaches
of North Carolina consumed Weakfish, Atlantic Croaker, Spot, inshore squid,
and Striped Anchovy, varying in abundance throughout year (Gannon 2003,
Gannon and Waples 2004). Mead and Potter’s (1990) study that included samples
from North Carolina, also identified Weakfish, Atlantic Croaker, and Spot
as primary dietary components. Although Weakfish was a primary dietary
component of oceanic dolphins in North Carolina, dolphins in the coastal region
of this study consumed less than 2%. This smaller quantity observed in
South Carolina dolphins is likely due to the fish’s distribution patterns along
the Eastern US coastline, as Weakfish congregate in much larger numbers off
North Carolina and points north.
Bottlenose Dolphins’ diets appeared to reflect seasonal fluctuations in available
prey. A similar seasonal trend in the diet of living dolphins in the estuarine
and near-shore coastal waters around Charleston, SC, was also detected using
blubber fatty acid analysis (Recks 2004). In this study, Star Drum was found in
all four seasons, but was the most dominant prey in winter (67%) and the lowest
in the summer (11%). Star Drum is the most abundant demersal fish species
occurring in estuarine waters (Wenner et al. 1984), remaining in estuaries when
many other fish species migrate offshore during cooler months, thereby restricting
dolphins with little other choice for food resources inside estuaries.
Spot was consumed significantly more in the fall by Bottlenose Dolphins in
this study. Recks’ (2004) study also found Spot to be consumed significantly
more during summer and fall. Spot are an estuarine-dependent species abundantly
occurring in South Carolina inshore waters, second only to Star Drum.
These fish are considered year-round residents of South Carolina waters (Dawson
18 Southeastern Naturalist Vol. 11, No. 1
1958, Keiser 1976). Adult fish exhibit seasonal shifts in distribution between the
coastal ocean and estuary with young-of-the-year remaining in estuaries during
their first winter. Shrimp trawl surveys show an abundance of Spot caught during
fall months during which large schools of migrating fish appear along South
Carolina beaches. Larger Spot spawn offshore during winter months, accounting
for its absence in the winter dolphin samples (Dawson 1958).
Bottlenose Dolphins have frequently been sighted following and feeding in
association with shrimp trawlers (Caldwell and Caldwell 1972; Corkeron et al.
1990; Fertl 1994; Gunter 1942, 1951; Leatherwood 1975). Shrimp is the most
valuable fishery in the near-shore coastal waters of South Carolina (SCDNR
2006). Its season extends from approximately May through January in the coastal
waters from Georgetown, SC to the Georgia/South Carolina border (Keiser
1976). During a long-term photo-identification study of Bottlenose Dolphins
near Charleston, twenty percent of the dolphin sightings between June and November
showed association with shrimp trawlers (Speakman et al. 2006).
While a wide variety of species are caught incidentally in the fishery trawls,
the Sciaenids were the predominant family of fishes in the composition (representing
approximately 60% of the catch) of discarded “trash” fish (Keiser 1976)
and were the family of fishes most consumed by dolphins in this study. Bay Anchovy,
Brief Squid, Star Drum, Silver Perch, Weakfish, Spot, Atlantic Croaker,
and Southern Kingfish are all species considered by-catch of local shrimp
trawlers (Keiser 1976) and are among the species caught most prevalently in
independent-fishery surveys along the South Atlantic Bight (SCDNR SEAMAP).
These individual species were among the most-consumed prey items in the diets
of Bottlenose Dolphins in South Carolina, indicating that dolphins may be taking
advantage of the food resource provided by trawling efforts.
In this study, shrimp was consumed more often by dolphins that stranded
in the oceanic region where shrimp trawling occurs. Recks (2004) found the
fatty acid profiles of dolphins sampled behind shrimp boats were distinct from
estuarine dolphins. Although dolphins in this study consumed shrimp, the
amount recovered from the stomach contents in relation to the proportion of
fish was small. The large proportion of by-catch consumed would suggest that
the dolphins were not targeting shrimp. Rather, it would suggest they were indirectly
consuming some shrimp while targeting fish caught in the nets of the
This study provided the first comprehensive characterization of the diet of
Bottlenose Dolphins collected in the waters of South Carolina. Although the results
of this study cannot be used to provide conclusive proof that the prey items
consumed by stranded dolphins are representative of a Bottlenose Dolphin population
at large, it does lend support to that hypothesis. The wide range of species
identified from stomach remains indicate food habits that incorporate a variety
of prey known to inhabit the estuarine and coastal waters of South Carolina. The
prey items consumed by Bottlenose Dolphins are also fish species consumed by
2012 S.M. Pate and W.E. McFee 19
humans and some dolphins have been found to have high contaminant loads.
From a human health aspect, knowing what these animals eat may also assist
in determining dolphin forage areas, and knowledge of this forage area may be
important when analyzing unusual mortality events. Investigations of unusual
mortality events can serve as indicators of ocean health and lead to further potential
implications on human health.
The lead author gratefully acknowledges the assistance provided by L. Burdett, J.W.B.
Powell, M.A. Recks, L.B. Rust, J.A. Stephen, and especially that of W.A. Roumillat. The
authors thank the South Carolina Marine Mammal Stranding Network, and the SCDNR
Inshore Fisheries and SEAMAP groups. The authors also thank W.A. Roumillat, P. Fair, G.
Seaborn. and E. Zolman for comments on earlier versions of this manuscript. This research
was made possible through NOAA’s responsibility under the Marine Mammal Health and
Stranding Response Act, Section 109(h) of the Marine Mammal Protection Act.
Disclaimer: This publication does not constitute an endorsement of any commercial
product or intend to be an opinion beyond scientific or other results obtained by the National
Oceanic and Atmospheric Administration (NOAA). No reference shall be made to
NOAA, or this publication furnished by NOAA, to any advertising or sales promotion
which would indicate or imply that NOAA recommends or endorses any proprietary
product mentioned herein, or which has as its purpose an interest to cause the advertised
product to be used or purchased because of this publication.
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