Stomach contents of small cetaceans
stranded along the Sea of Oman and Arabian
Sea coasts of the Sultanate of Oman
louisa s. ponnampalam
, tim j.q. collins
, gianna minton
, isabelle schulz
, rupert f. g. ormond
and robert m. baldwin
Environment Society of Oman, PO Box 3955, P.C. 112, Ruwi, Sultanate of Oman,
University Marine Biological Station Millport,
Isle of Cumbrae, Scotland KA28 0EG,
Institute of Ocean and Earth Sciences, C308, IPS Building, University of Malaya, 50603 Kuala
Ocean Giants Program, Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, New York 10460, USA,
Institute of Biodiversity and Environmental Conservation, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia,
Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, D-27570 Bremerhaven, Germany,
Conservation International, 5/6 Lang Rigg South Queensferry, Edinburgh, Scotland EH30 9WN,
School of Biomedical Sciences,
University of Durham, South Road DH1 3LE
This study examined the stomach contents of 11 bottlenose dolphins (Tursiops sp.), ﬁve Indo-Paciﬁc humpback dolphins
(Sousa chinensis) and two spinner dolphins (Stenella longirostris) that were found stranded along the Omani coastline.
Across the three species examined, a total of 4796 ﬁsh otoliths and 214 cephalopod beaks were found, representing at least
33 species in 22 families. Prey item importance was calculated using the percentage by number and percentage by frequency
of occurrence methods, and a modiﬁed index of relative importance. The ﬁsh families Apogonidae, Carangidae and
Scombridae were the most numerically important prey of the bottlenose dolphins. Sciaenidae was the most numerically
important ﬁsh family for the Indo-Paciﬁc humpback dolphins. The myctophid Benthosema pterotum formed the majority
of the prey items of spinner dolphins. Cephalopod remains found in the stomach samples were represented by the families
Sepiidae, Loliginidae and Onychoteuthidae. The known depth distribution of prey items of bottlenose dolphins indicated
that the animals fed in a wide variety of habitats. Indo-Paciﬁc humpback dolphin prey items indicated feeding in shallow
coastal areas. Spinner dolphins appear to have exploited the upper 200 m of the water column for food, where their vertically
migrating mesopelagic prey are found at night. Most prey species found in the stomach contents do not appear to be of current
commercial importance in Oman. However, the ﬁndings here indicated that all three species of dolphins were feeding in areas
where artisanal and/or commercial ﬁshing occurs and has conservation implications.
Keywords: cetaceans, stomach contents, diets, feeding, habitat, Sea of Oman, Gulf of Masirah, Oman
Submitted 20 October 2011; accepted 24 November 2011; ﬁrst published online 6 February 2012
Dietary analysis is an important aspect of research into the
feeding ecology of animals. It enables the quantiﬁcation of a
species’ nutritional needs (Benoit-Bird, 2004), and of the
amount of food consumed by an individual or population
(Hyslop, 1980). It also enables the estimation of predation
pressure on the prey fauna (Robison & Craddock, 1983) and
in the case of cetaceans, assists in the exploration of the
hypothesis that distribution is closely linked to the distri-
bution and abundance of prey (Hui, 1985; Selzer & Payne,
1988; Bowen & Siniff, 1999). Methods of studying the
feeding ecology of cetaceans include stable-isotope and fatty
acids composition analysis (Nin
˜o-Torres et al., 2006), trace
metal measurements (Lahaye et al., 2005), fecal analysis
(Smith & Whitehead, 2000) and the examination of stomach
contents (Di Beneditto & Siciliano, 2007).
Overall, relatively little study has been conducted on the
diets of cetaceans in the northern Indian Ocean. Baldwin
(2003) brieﬂy mentioned the stomach contents of bottlenose
dolphins (Tursiops truncatus) and Indo-Paciﬁc humpback
dolphins (Sousa chinensis) found on Merawah and Bu Tina
Islands in Abu Dhabi. Robineau & Fiquet (1994) examined
the stomach contents of a single juvenile male bottlenose
dolphin found along the Arabian Gulf coast of Saudi Arabia.
There is also some published information on the diets of
marine cetaceans in India, comprising studies on the
stomach contents of eight cetacean species collectively, includ-
ing the three species examined here (Natarajan & Rajaguru,
1983, 1985; Karbhari et al., 1985; Silas et al., 1985;
Krishnapillai & Kasinathan, 1987; Krishnan et al., 2007). A
thorough search of the literature on marine cetacean dietary
studies revealed no results for Pakistan, Iran and Sri Lanka.
To date, knowledge about the diets of cetaceans in the
Sultanate of Oman is very limited, though there have been
basic observations of feeding behaviour (Salm, 1991;
Baldwin et al., 1998, 2004). This study analyses the stomach
contents of stranded, beach-cast bottlenose dolphins
Journal of the Marine Biological Association of the United Kingdom, 2012, 92(8), 1699–1710. #Marine Biological Association of the United Kingdom, 2012
(Tursiops sp.), Indo-Paciﬁc humpback dolphins (Sousa chi-
nensis) and spinner dolphins (Stenella longirostris) with the
aims of better understanding the distribution and patterns
of habitat use of these dolphin species in Oman, of assessing
whether the dolphins could be competing with local ﬁsheries
for resources, and of considering whether there is evidence of
niche partitioning between dolphin species with overlapping
MATERIALS AND METHODS
Sample collection sites
Stomach contents samples were collected from cetaceans
found during dedicated and opportunistic beach surveys
along the Oman coastline, and opportunistically during any
stranding events that were reported. Dedicated surveys were
conducted from 2000 to 2003, covering 534 km of beaches
from Muscat in the north, to Dhofar, and from 2005 to
2006, covering over 565 km of beaches from As Sahm on
the Al Batinah coast, south to the island of Masirah. These
surveys yielded a total of 18 individual carcasses representing
three species; the bottlenose dolphin, Indo-Paciﬁc humpback
dolphin and spinner dolphin and provided the samples exam-
ined in this study (Figure 1). The carcasses were found in
varying states of decomposition and were therefore categor-
ized according to ‘stranding states’, using deﬁnitions provided
by Geraci & Lounsbury (2005) (Table 1).
collection of stomach contents samples
Stranded beach-cast cetaceans were dissected in situ upon dis-
covery, to locate any food remains in the stomach and oeso-
phagus following established methods for stomach contents
collection (e.g. Sekiguchi, 1995; Dolar et al., 2003). The
stomach and oesophagus were ﬁrst removed from the body
cavity. To ensure that prey items were not lost upon
removal, the stomach and oesophagus were turned inside
out, placed over a series of simple kitchen sieves with a
maximum mesh size of 2 mm and rinsed thoroughly using a
hose. If available, otoliths were extracted directly from the
intact skulls of ﬁsh in the sample while length measurements
of whole or semi-digested prey that was still relatively intact
were taken. Stomach contents with whole or semi-digested
prey were left soaking in water for a few days, and then
rinsed to separate the soft tissues of the prey items from the
bony parts. The samples were then sieved multiple times
over a collecting tray using sieves of decreasing mesh size,
reducing the stomach contents to cephalopod beaks, ﬁsh oto-
liths, ﬁsh scales and bones. The otoliths, ﬁsh scales and bones
were then left to dry, while cephalopod beaks were stored in
70% ethanol. Eight of the stomachs were full, seven were
less than half-full, and no information on stomach fullness
was available for the remaining two stomach samples that
were collected by associate researchers (Table 1).
Identiﬁcation and enumeration of prey items
Each dried stomach contents sample was sorted into ﬁsh oto-
liths, ﬁsh dentary bones, other ﬁsh bones and scales, and
cephalopod beaks. The otoliths and dentary bones were
sorted into left and right, while the beaks were sorted into
upper and lower, and these were itemized. Otoliths were
further sorted according to type (i.e. shape, size and
pattern), and matched into pairs when both left and right
sides of equal sizes were available (i.e. one right and left
otolith that matched in pattern and size equated to one
otolith pair). The number of ﬁsh eaten was estimated by
counting the number of otolith pairs plus any other unpaired
otoliths (i.e. each otolith pair was considered to be one ﬁsh,
while remaining unpaired otoliths that were different from
each other in pattern and size were counted as one ﬁsh
each). Due to their very small size and high abundance, the
otoliths in each spinner dolphin sample were tallied and
divided by two to estimate the total number of ﬁsh consumed
(Dolar et al., 2003). The higher count of either upper or lower
cephalopod beaks in each sample was used to estimate the
number of cephalopods consumed (Pinkas et al., 1971;
Dolar et al., 2003; Amir et al., 2005). Fish dentary bones
were used to estimate the number of ﬁsh consumed when a
sample did not contain any otoliths. In samples where both
otoliths and ﬁsh dentary bones were available, the dentary
bones were identiﬁed and included in the analysis only if
they did not match with any species that had already been
identiﬁed by otoliths.
Otoliths were identiﬁed to the lowest taxonomic level poss-
ible using Smale et al. (1995) while cephalopod beaks were
identiﬁed to the lowest taxonomic level possible using
Clarke (1986) and Kubodera (2005). Reference collections
speciﬁc to Oman and the Middle East are not available. The
identiﬁcation of ﬁsh dentary bones was made by K.
Longenecker (Bishop Museum, Honolulu, Hawaii, USA).
Cephalopod beaks that could not be identiﬁed were sent to
˜a Santos (Centro Oceanogra
´ﬁco de Vigo, Spain)
and S. Plo
¨n (South African Institute for Aquatic
Biodiversity), but remained unidentiﬁed due to the absence
of matching samples from their respective work regions.
Fish classiﬁcation and information on ﬁsh distribution and
habitat followed Al-Abdessalam (1995) and Randall (1995)
while similar information for cephalopods followed
Al-Abdessalam (1995) and Jereb & Roper (2005). An
attempt was made to use ﬁsh otolith lengths, and rostral
and hood lengths of cephalopod beaks to back-calculate the
masses and standard lengths of the ﬁsh and cephalopods
that were consumed. However, due to the lack of available
regression equations and allometric coefﬁcients for most of
the ﬁsh species and various cephalopod species in Oman,
these measurements were not utilized in this study.
Calculation of prey importance
Following the equations used in Sekiguchi (1995) and Amir
et al. (2005), three different indices were used to quantify
the occurrence and relative importance of prey items in the
stomachs: (1) percentage by number (%N); (2) percentage fre-
quency of occurrence (%FO); and (3) the modiﬁed index of
relative importance (IRI).
Percentage by number (%N) is the calculation of the
numerical abundance (%N
) of each prey species present in
the diet. This was calculated as:
is the number of prey species ipresent in stomach j,
is the total number of prey present in stomach j.
Percentage frequency of occurrence (%FO) is the calcu-
lation of the frequency of occurrence of each prey species
1700 louisa s. ponnampalam et al.
) within the stomach samples. This was calculated as:
is the frequency of stomachs i containing prey j,
is the total number of stomachs containing prey
The index of relative importance is a rank measure of the
importance of different prey species in the diet. This was cal-
culated as a modiﬁed version of Pinkas et al. (1971)
(in Sekiguchi (1995)):
Percentage similarity (PS) was calculated to investigate
dietary overlap between stomachs of the same species, as
well as interspeciﬁc dietary overlap, using the equation in
Silver (1975). This was calculated as:
PSab =Smin(%Nia,%Nib )
Fig. 1. Maps showing (inset) the location of Oman, and the locations at which stomach contents of stranded bottlenose, Indo-Paciﬁc humpback and spinner
dolphins were collected during dedicated and incidental beach surveys in (A) Muscat/Sea of Oman and (B) Gulf of Masirah regions. Numbers in parentheses
in the legends indicate the sample size for each dolphin species. Depth contours are in metres.
stomach contents of cetaceans in oman 1701
where a and b represent different stomachs and i represents
the prey species.
A total of 4796 ﬁsh otoliths and 214 cephalopod beaks (upper
and lower) were found in the 18 stomachs (across all three
species) of cetaceans examined. No crustacean or other
remains were found. Eleven stomachs of bottlenose dolphins
were examined, of which 18.0% (2) contained only ﬁsh
remains, 27.0% (3) contained only cephalopod remains, and
55.0% (6) contained both ﬁsh and cephalopod remains. In
terms of number, 71.0% of the diet of bottlenose dolphins com-
prised ﬁsh, while the remainder 29.0% comprised cephalopods.
A total of ﬁve stomachs of Indo-Paciﬁc humpback dolphins
were examined, of which 20.0% (1) contained both ﬁsh and
cephalopod remains, while 80.0% (4) of stomachs contained
only ﬁsh remains. In terms of number, 87.0% of the diet of
humpback dolphins comprised ﬁsh, while the remaining
13.0% comprised cephalopods. Two stomachs of spinner dol-
phins were examined, and both ﬁsh and cephalopod remains
were found in each. Combining data from the two specimens,
99.0% of the total number of prey remains found in the
spinner dolphin stomachs comprised ﬁsh, while the remaining
1.0% comprised cephalopods. There was not any prey species
overlap between bottlenose dolphins and spinner dolphins or
between Indo-Paciﬁc humpback dolphins and spinner dolphins.
Only one prey species overlapped between bottlenose dolphins
and Indo-Paciﬁc humpback dolphins (i.e. Otolithes ruber)and
one genus overlapped between bottlenose dolphins and
spinnerdolphins(i.e.Apogon). However, the total percentage
number of Apogon ﬁsh found in the stomachs of bottlenose dol-
phins was much higher than in spinner dolphins (56.1% versus
A total of 416 whole sagittal otoliths from an estimated 228
individual ﬁsh were found in the stomachs of eight of the 11
bottlenose dolphins sampled (Table 2). These represented 22
species of teleost ﬁsh distributed across 20 genera and 14
families. Numerically, the most important prey family was
the Apogonidae (cardinalﬁsh), in which two of three species
present, Apogon cyanosoma and A. multitaeniatus, accounted
for 55.2% of all ﬁsh prey consumed (Table 2). Apogonidae,
Scombridae and Sciaenidae were the most frequently occur-
ring families (36.4% each) (Table 2). Of the otoliths found
in the bottlenose dolphins’ stomachs, 1.4% were broken or
degraded severely, preventing identiﬁcation and were thus
not included in analysis.
In terms of relative importance, the family Apogonidae had
the highest modiﬁed IRI (2042.0) (Table 2). Apogon multitae-
niatus ranked ﬁrst in terms of number (32.0%) and had the
highest modiﬁed IRI (582.4), although Otolithes ruber,
Scomber japonicus and Terapon jarbua occurred more fre-
quently (27.3% each). Apogon cyanosoma ranked second in
terms of number and modiﬁed IRI (23.2%, 422.2), but also
did not occur as frequently as the former three species.
Carangoides malabaricus ranked third in terms of number
(11.8%), but only occurred in one stomach (%FO ¼9.1),
whereas O. ruber,S. japonicus and T. jarbua each made up
only approximately 6.0% in terms of number, though the
three ranked ﬁrst in frequency of occurrence. Otolithes ruber
also had a higher modiﬁed IRI than C. malabaricus (166.5
versus 107.4). One prey species (Epinephelus sp.) only
accounted for ,5.0% in terms of number while all other
prey species found in the stomachs accounted for ,1.0%
each in terms of number (Table 2). The average number of
ﬁsh prey taxa per stomach was 3.6 (+SD 1.6). The number
of ﬁsh prey items found per stomach ranged from 0 – 127
(mean ¼21.1, +SD 37.2, N ¼11). Percentage similarity
(PS) calculations across dolphin samples revealed low levels
of overlap in ﬁsh prey species found in the diet. Only one
pair of stomachs, both from individuals from the Gulf of
Masirah, had PS .50.0%, while 19 of the 28 stomach pairs
(67.9%) had a PS of 0.0. The stomach contents of the single
dolphin from Muscat (Sea of Oman) had a PS of 0.0 compared
with all the other stomach contents of the Gulf of Masirah dol-
phins (Table 3) and its mainly pelagic prey species are
Table 1. Summary of stomach samples analysed. Stranding state (SS) deﬁnition (i.e. code for condition of animal/carcass) is based on Geraci &
Lounsbury (2005). SS: 1 ¼live animal; 5 ¼skeletal remains. Stomach fullness (SF): 8/8 ¼full.
Sample number Species Sex Body length (cm) Location SS (1–5) SF ( 8/8)
26-05-01-03 Tursiops sp. U 196 Barr al Hikman 5 N/A
29-09-01-05 Tursiops sp. U N/A Barr al Hikman 4 8
29-09-01-06 Tursiops sp. M 260 Barr al Hikman 4 8
04-10-01-01 Tursiops sp. M 253 Masirah Island 3 1
09-10-01-01 Tursiops sp. U 246 Masirah Island 5 N/A
22-10-01-09 Tursiops sp. U 216 Masirah Island 4 8
01-11-01-01 BaH Tursiops sp. U N/A Barr al Hikman 5 8
01-11-01-03 BaH Tursiops sp. M 220 Barr al Hikman 5 8
05-11-01-01 Tursiops sp. M 210 Khaluf 5 8
15-02-06-01 Tursiops sp. M 226 Masirah Island 3 8
02-05-06-01 Tursiops sp. U 275 Muscat 3 8
16-12-01-01A Sousa chinensis F 268 Khaluf 2 3
16-12-01-05A Sousa chinensis F 257 Khaluf 3 3
29-12-01-05 Sousa chinensis M 250 Khaluf 3 1
29-12-01-06 Sousa chinensis F 245 Khaluf 4 2
24-02-06-02 Sousa chinensis U 226 Masirah Island 5 ,1
27-08-05-01 Stenella longirostris M 171 Al Batinah 4 8
27-08-05-02 Stenella longirostris M 130∗Al Batinah 3 3
∗, length measured to caudal peduncle, as tail ﬂukes had been severed; U, unidentiﬁed; M, male; F, female.
1702 louisa s. ponnampalam et al.
indicated in Table 2. A total of 174 cephalopod beaks from 95
cephalopods (squids and cuttleﬁsh) were found in nine of the
11 bottlenose dolphin stomachs examined, all of which were
from the Gulf of Masirah. These beaks represented at least
four species in two genera and two families, namely the
Sepiidae and Loliginidae (Table 2). There were three other
unidentiﬁed species that accounted for 60.0% (48) of the
lower beaks that were analysed.
indo-pacific humpback dolphins
A total of 21 otoliths from 13 teleost ﬁsh were found in the
stomachs of the ﬁve Indo-Paciﬁc humpback dolphins
sampled (Table 4). These represented ﬁve species in four
genera and three families that occur predominantly in
turbid, shallow water habitats. Numerically, the most impor-
tant prey family was Sciaenidae (53.9%), followed by Ariidae
(30.8%) and Synodontidae (15.4%). The most frequently
occurring prey family was Sciaenidae (100.0%). Arius sp.
was the most important prey species in terms of number
(30.8%) though it only had a frequency of occurrence of
20.0%. The sciaenids Johnius sp. and Otolithes ruber each
ranked second in terms of number (23.1%). However, O.
ruber occurred more frequently than Johnius sp. (60.0%
versus 40.0%) (Table 4). Otolithes ruber had the highest modi-
ﬁed IRI (1384.8), followed by Johnius sp. (923.2) and Arius sp.
(615.4) (Table 4). The average number of ﬁsh prey taxa per
stomach was 1.4 (+SD 0.9). The number of ﬁsh prey items
found per stomach ranged from 1 – 7 (mean ¼2.6, +SD
2.6, N ¼5). PS calculations across samples revealed minimal
overlap in ﬁsh prey species found in the stomachs. Only one
pair of stomachs had PS .50.0%, while 6 of the 10 stomach
pairs had a PS of 0.0 (Table 3). Only one of the ﬁve
Indo-Paciﬁc humpback dolphin stomachs that were examined
contained cephalopod beaks. These comprised one upper and
two lower beaks and represented two squids in total, but were
not successfully identiﬁed due to a lack of comparable beaks
from the region.
A total of 4355 sagittal otoliths from 2179 ﬁshes were found in
the stomachs of the two spinner dolphins sampled (Table 5).
These represented ﬁve species in at least four genera and four
families of teleost ﬁsh that occurred almost entirely in meso-
pelagic water depths. The Myctophidae was the most impor-
tant prey family in terms of number and frequency of
occurrence (99.4% and 100.0% respectively). Due to the
small sample size of two dolphins, the modiﬁed IRI for
spinner dolphins was not calculated. A total of 23 upper
beaks and 14 lower beaks were retrieved from both spinner
dolphins that were sampled. These all represented
Onychoteuthis banksi from the family Onychoteuthidae
The results show that the bottlenose dolphins examined in this
present study consumed a relatively large variety of prey
(Table 2). However, it was evident that the diet of dolphins
from the Gulf of Masirah and of the single animal from
Muscat differed in terms of preferred habitat of prey species.
The depth distributions of the majority of prey species of bot-
tlenose dolphins from the Gulf of Masirah suggest that the
dolphins there fed primarily in shallow, coastal inshore
waters and over the continental shelf (Al-Abdessalaam,
1995; Randall, 1995). Conversely, the bottlenose dolphin
that stranded in the Muscat capital area had primarily eaten
Table 2. Percentage number and percentage frequency of occurrence of
ﬁsh and cephalopod families and species found in stomachs of bottlenose
dolphins. IRI, index of relative importance; n
, total number of stomachs
containing prey items; ∗, prey items of sole bottlenose dolphin found in
Muscat; ∗∗, lower beak count.
Prey species N %
Family Apogonidae 128 56.1 4 36.4 2042.0
Apogon cookii 2 0.9 2 18.2 16.4
Apogon cyanosoma 53 23.2 2 18.2 422.2
Apogon multitaeniatus 73 32.0 2 18.2 582.4
Family Carangidae 29 12.7 2 18.2 231.1
27 11.8 1 9.1 107.4
Selar crumenophthalmus 2 0.9 1 9.1 8.2
Family Engraulidae 2 0.9 2 18.2 16.4
Thryssa setirostris 2 0.9 2 18.2 16.4
Family Gerreidae 1 0.4 1 9.1 3.6
Gerres oyena 1 0.4 1 9.1 3.6
Family Kyphosidae 1 0.4 1 9.1 3.6
Kyphosid 1 1 0.4 1 9.1 3.6
Family Mullidae 2 0.9 2 18.2 16.4
Parupeneus rubescens 1 0.4 1 9.1 3.6
Upeneus tragula∗1 0.4 1 9.1 3.6
Family Nemipteridae 1 0.4 1 9.1 3.6
Scolopsis vosmeri 1 0.4 1 9.1 3.6
Family Sciaenidae 16 7.0 4 36.4 254.8
Otolithes ruber 14 6.1 3 27.3 166.5
Umbrina canariensis 2 0.9 2 18.2 16.4
Family Scombridae 19 8.3 4 36.4 302.1
Gymnosarda unicolor∗1 0.4 1 9.1 3.6
Katsuwonus pelamis 3 1.3 1 9.1 11.8
Scomber japonicus 14 6.1 3 27.3 166.5
Thunnus albacares∗1 0.4 1 9.1 3.6
Family Serranidae 9 3.9 1 9.1 35.5
Epinephelus sp. 9 3.9 1 9.1 35.5
Family Sparidae 2 0.9 1 9.1 8.2
Crenidens crenidens 2 0.9 1 9.1 8.2
Family Sphyraenidae 1 0.4 1 9.1 3.6
Sphyraena jello 1 0.4 1 9.1 3.64
Family Teraponidae 15 6.6 3 27.3 180.2
Terapon jarbua 15 6.6 3 27.3 180.2
Family Trichiuridae 2 0.9 2 18.2 16.4
Trichiurus lepturus 2 0.9 2 18.2 16.4
Fish totals 228 100.0
Family Sepiidae 30 37.5 8 72.7 2727.3
Sepia pharaonis 23 28.8 7 63.6 1831.7
Sepia latimanus 5 6.3 2 18.2 114.7
Sepia sp. 2 2.5 2 18.2 45.5
Family Loliginidae 2 2.5 1 11.1 22.7
Loligo sp. 2 2.5 1 9.1 22.7
Unidentiﬁed sp. 1 2 2.5 1 9.1 27.8
Unidentiﬁed sp. 2 38 47.5 4 36.4 1727.3
Unidentiﬁed sp. 3 8 10.0 3 27.3 272.7
Cephalopod totals 80∗∗ 100.0
Total 308 100.0 n
stomach contents of cetaceans in oman 1703
scombrids, which is a family of pelagic and epipelagic ﬁsh
(Nelson, 1994). Both cephalopod families found in the
stomachs of the Gulf of Masirah bottlenose dolphins are typi-
cally found nearshore and over continental shelf waters.
However the Sepiidae are primarily demersal while
Loliginidae are primarily neritic (Jereb & Roper, 2005).
The ﬁndings in the stomach contents of bottlenose dol-
phins suggest that this species tends to exploit the upper
200 m for food in a wide variety of habitats. The relatively
high number of apogonids and the cuttleﬁsh Sepia pharaonis,
and high variety of other reef-associated ﬁsh species such as
Terapon jarbua and Scomber japonicus in the diet of Gulf of
Masirah dolphins suggest that those dolphins may have
favoured areas around coral reefs (Al-Abdessalaam, 1995).
Additionally, their diet also comprised species such as the
croaker Otolithes ruber, that occur on sandy and muddy sub-
strates (Al-Abdessalaam, 1995), which is consistent with the
environment in the northern portion of the Gulf of Masirah
where most of the bottlenose dolphin specimens were
found. This shallow sheltered area and the adjacent central
part of the Gulf of Masirah, is highly productive and food is
unlikely to be scarce (Banzon et al., 2004). Most ﬁsh species
consumed by the dolphins that stranded in the Gulf of
Masirah were diurnal (Al Abdessalaam, 1995; Randall,
1995). However, the occurrence of several nocturnal and
benthopelagic species in those stomachs suggest that the dol-
phins hunted during both day and night, perhaps in concert
with circadian migrations of ﬁsh to and from the surface.
The purely piscivorous diet of mostly larger, pelagic scom-
brids, all of which are diurnal species (Al-Abdessalaam,
1995), suggests that the dolphin that stranded in Muscat
had fed during the day probably in deeper waters.
Demersal, soniferous ﬁsh families, such as Sparidae and
Sciaenidae form the dietary basis for bottlenose dolphins in
the Paciﬁc region (Walker, 1981; Barros & Wells, 1998).
Similarly, sciaenids appeared to be important in the diet of
bottlenose dolphins found stranded in the Gulf of Masirah,
while sparids were also found in their food items. Five of
the nine ﬁsh families consumed by offshore bottlenose dol-
phins in Hong Kong were represented in the stomach contents
of the Gulf of Masirah bottlenose dolphins (i.e. Apogonidae,
Carangidae, Trichiuridae, Sparidae and Serranidae).
Additionally, there were three genera (i.e. Apogon,Trichiurus
Table 3. Percentage similarity (PS) values for ﬁsh prey species between bottlenose dolphin stomachs that were analysed and between Indo-Paciﬁc
humpback dolphin stomachs that were analysed.
PS values for bottlenose dolphin samples
Sample number 26-05-01-03 29-09-01-05 29-09-01-06 04-10-01-01 01-11-01-01 05-11-01-01 15-02-06-01
29-09-01-06 0.0 15.4
04-10-01-01 0.0 15.5 0.0
01-11-01-01 36.4 24.5 0.0 0.0
05-11-01-01 20.0 46.2 0.0 4.0 61.1
15-02-06-01 0.0 0.0 2.5 0.0 0.0 0.0
02-05-06-01 0.0 0.0 0.0 0.0 0.0 0.0 0.0
PS values for indo-paciﬁc humpback dolphin samples
Sample number 16-12-01-01A 16-12-01-05A 29-12-01-05 29-12-01-06
29-12-01-05 0.0 0.0
29-12-01-06 33.3 14.3 66.7
24-02-06-02 0.0 0.0 0.0 0.0
Table 4. Percentage number and percentage frequency of occurrence of
ﬁsh families and species found in stomachs of Indo-Paciﬁc humpback dol-
phins. IRI, index of relative importance; n
, total number of stomachs con-
taining prey items.
Prey species N %
Family Ariidae 4 30.8 1 20.0 615.4
Arius sp. 4 30.8 1 20.0 615.4
Family Sciaenidae 7 53.8 5 100.0 5385.0
Johnius sp. 3 23.0 2 40.0 923.2
Otolithes ruber 3 23.0 3 60.0 1384.8
1 7.7 1 20.0 153.8
2 15.4 1 20.0 307.6
2 15.4 1 20.0 307.6
Total 13 100.0 n
Table 5. Percentage number and percentage frequency of occurrence of
ﬁsh and cephalopod families and species found in stomachs of spinner
, total number of stomachs containing prey items. Modiﬁed
index of relative importance not calculated due to small sample size.
Prey species N % number F % frequency
Family Apogonidae 1 0.05 1 50.0
Apogon semiornatus 1 0.05 1 50.0
Family Gempylidae 8 0.4 1 50.0
Neoepinnula orientalis 8 0.4 1 50.0
Family Myctophidae 2165 99.4 2 100.0
Benthosema pterotum 2165 99.4 2 100.0
Family Nomeidae 1 0.05 1 50.0
Cubiceps pauciradiatus 1 0.05 1 50.0
Unidentiﬁed sp. 1 4 0.2 1 50.0
Fish totals 2179 100.0
Family Onychoteuthidae 23 100.0 2 100.0
Onychoteuthis banksi 23 100.0 2 100.0
Total 2202 100.0 n
1704 louisa s. ponnampalam et al.
and Epinephelus) and one species of ﬁsh (i.e. Trichiurus lepturus)
that offshore bottlenose dolphins in both Hong Kong and the
Gulf of Masirah had consumed in common (see Barros et al.,
2000). Of the 34 ﬁsh families found in the stomach contents
of Indo-Paciﬁc bottlenose dolphins in Zanzibar, eight were
also represented in the stomach contents of the Gulf of
Masirah dolphins, while there were four genera (i.e. Apogon,
Carangidae,Gerres and Saurida) in common between the two
populations. Additionally, only one (Apogonidae) of those
eight families was important for dolphins from both areas. In
India, the stomach of a bottlenose dolphin also contained predo-
minantly sciaenids (Natarajan & Rajaguru, 1985).
The lack of similarity in the stomach contents of all the
Gulf of Masirah specimens and the Muscat specimen may
be a reﬂection of the presence of two species of bottlenose dol-
phins (T. aduncus and T. truncatus) in Oman occupying two
different habitats. Although tissue samples for genetic analysis
and cranial material for taxonomic measurements were routi-
nely collected when available and feasible, other factors,
including sample degradation and the absence of cranial
remains, precluded identiﬁcation of carcasses to species
level. Bottlenose dolphin specimens used here were typically
in either advanced stages of decomposition or located on
very remote beaches with little opportunity for collection of
skeletal remnants. Nonetheless photographs and observations
of live sightings of bottlenose dolphins during small-boat
surveys in the Gulf of Masirah between 2000 and 2006
suggest that it is most likely that T. aduncus inhabits the
shallow waters (mostly in depths of less than 20 m) of this
large bay. Individuals had estimated body lengths of less
than 3 m, had slender rostra, prominent ventral spotting
and physically resembled T. aduncus as described in Wang
et al. (2000) (Ponnampalam, 2009; Minton et al., 2010).
Those sighting depths were consistent with the reported pre-
ferred depth of T. aduncus (Findlay et al., 1992; Wells & Scott,
2002). The dolphin found stranded in Muscat was also less
than 3 m long. However, it was the largest of all bottlenose
dolphins examined in this study and at 2.75 m length
(Table 1), exceeded the maximum recorded length of T.
aduncus as reported by Wang et al. (2000). We consider it
likely that this specimen, which was more robust, stocky
and blunt-nosed, was a T. truncatus. Its diet, consisting
mainly of a variety of pelagic tuna, reﬂects that it was
almost certainly feeding off the Muscat coast. There the con-
tinental shelf is narrow, depths greater than 200 m can be
found within 10 km from shore (Figure 1) and ﬁshermen
are often seen hand-lining for yellowﬁn and longtail tuna
within 5 km of the coast. Examination of its mouth showed
that all teeth were erupted, though not worn, a sign that the
dolphin was a sub-adult, and could possibly attain more
than 3 m in length when fully grown. Ponnampalam (2009)
and Minton et al. (2010) have previously reported that bottle-
nose dolphins sighted in the Muscat region are stocky, blunt-
nosed and heavily scarred, some of which had estimated body
lengths exceeding 3 m and resembled T. truncatus.
Skin samples taken from these dolphins await genetic ana-
lyses for conﬁrmation of species-level identiﬁcation. Until
then, no deﬁnitive conclusions can be made on their taxo-
indo-pacific humpback dolphins
The prey spectrum of Indo-Paciﬁc humpback dolphins exam-
ined here appeared to be small in comparison to bottlenose
dolphins and to consist mainly of coastal, inshore species that
inhabit murky waters with muddy substratum. The croaker
Otolithes ruber is a benthopelagic sciaenid species found in rela-
tively shallow and turbid waters (Al-Abdessalaam, 1995). The
other genus of sciaenid represented in the stomach contents
was Johnius. Randall (1995) reports four species of Johnius to
occur in Omani waters, all of which are demersal, coastal
species (Sasaki, 2001). The otoliths of sea catﬁsh (Ariidae)
that were found in one of the stomachs were too degraded to
enable species-level identiﬁcation. Randall (1995) reported
that sea catﬁsh in Oman are represented solely by the genus
Arius in four different species. All four species are demersal,
and mostly occur in shallow inshore, rocky and muddy
waters. Dead ariids ﬂoating at the surface, likely to be ﬁshing
discards, were often encountered during small-boat surveys in
the Gulf of Masirah (Ponnampalam, 2009).
Baldwin et al. (2004) showed a clustering of live sightings of
Indo-Paciﬁc humpback dolphins in the Ghubhat Hashish, a
semi-enclosed and shallow bay located in the northern
reaches of the Gulf of Masirah, particularly in the areas
around Mahawt Island and Khaluf, where groups of up to
50 animals were observed. Four of the ﬁve Indo-Paciﬁc hump-
back dolphins examined in this study were found on the beach
of Khaluf (see Figure 1). Acoustic watches conducted for ceta-
ceans during small-boat surveys in the Gulf of Masirah, par-
ticularly at stations situated between Khaluf and Barr al
Hikman, also yielded a variety of grunts and croaks typical
of soniferous ﬁsh species such as O. ruber and Johnius sp.
(Al-Abdessalaam, 1995). The sciaenids found in the Indo-
Paciﬁc humpback dolphin stomachs had the two highest
values of modiﬁed IRI of all the prey species found. It is
thus likely that the Gulf of Masirah, which is characterized
by very shallow (10 m), murky waters, particularly in the
northern portion where Indo-Paciﬁc humpback dolphins are
frequently sighted and occur in large groups, is a rich source
of food and provides important feeding grounds for this
species—direct observations of feeding activity in the area
further support this notion (Baldwin et al., 2004).
In this study, although the sample size was small and prey
species diversity was low, the Oman Indo-Paciﬁc humpback
dolphins showed some similarity in their mainly piscivorous
diet to other conspeciﬁcs. One study of stomach contents
from eight dolphins in Hong Kong revealed that 81% of the
almost entirely piscivorous diet was based on the families
Sciaenidae, Engraulidae and Clupeidae (Jefferson, 2000).
Another Hong Kong study reported that the dolphins con-
sumed trichiurids and ariids (Barros et al., 2004). In southern
China, Indo-Paciﬁc humpback dolphins were also found to be
preying mainly upon estuarine ﬁsh species (Wang, 1995).
Sciaenid ﬁsh were important to the Indo-Paciﬁc humpback
dolphins in both Hong Kong and Oman. There were
two prey genera in common between the dolphins in this
study and those from Hong Kong, one of which (Johnius)
was numerically important for both populations. The
Indo-Paciﬁc humpback dolphins in Xiamen Harbor, southern
China, had also consumed ﬁsh of the genus Johnius (Wang,
1995). Conversely, in India, an Indo-Paciﬁc humpback
dolphin incidentally caught in gill nets was found to have con-
sumed only teleost ﬁsh, although none of these were sciaenids
or ariids (Krishnan et al., 2007). Finding marine catﬁsh in the
stomachs of humpback dolphins in this study is interesting to
note. Barros et al. (2004) pointed out that the catﬁsh are a
‘bottom-dwelling species possessing dangerous spines
stomach contents of cetaceans in oman 1705
covered by a venomous mucus, capable of inﬂicting lacerating
wounds’ (Smith & Heemstra, 1986). Given the apparent abun-
dance of ariids in Oman, the dolphins may have adapted a way
to digest or avoid their venomous, spiny prey without harming
their stomachs and internal organs, taking advantage of a
possibly abundant food resource.
Myctophids, the primary prey items of both spinner dolphin
specimens examined here, are common and occur throughout
most of the world’s oceans (Dalpadado & Gjøsaeter, 1988;
McClatchie & Dunford, 2003). The Myctophidae is a family
of ﬁsh known to undertake daily vertical migrations from
bathypelagic (1000 – 4000 m) and mesopelagic (200 –
1000 m) depths during the day, to depths of 200 m up to
the surface during the night (Clarke, 1973; Paxton & Hulley,
1999). A survey in 1990 in the Sea of Oman by the RV
‘Rastrelliger’ found that myctophids were most abundant off
the Al Batinah coast (Johannesson, 1995), where the two
spinner dolphins examined in this study had been found
Gjøsaeter (1984) and Johannesson (1995) reported the
myctophid Benthosema pterotum to be the most abundant
and dominant mesopelagic species in the Sea of Oman.
Benthosema pterotum was also the only mesopelagic species
found in the vicinity of a ﬁxed station in the Sea of Oman
(Sætersdal et al., 1999). Another species found in the stomachs
of the spinner dolphins was the bathypelagic nomeid Cubiceps
pauciradiatus. It inhabits water depths between 58 and
1000 m but is found near the surface at night (Butler, 1979).
This species only contributed 0.4% in number among the
stomach contents, and may have been dispersed in the
dense schools of B. pterotum near the surface. The gempylid
Neoepinnula orientalis is found between 200 and 570 m
depth (Nakamura & Parin, 1993). It is not known if N. orien-
talis undertakes vertical migration towards the shallower
depths at night although some species of Gempylidae do
(Nakamura & Parin, 1993). Apogon semiornatus is an
inshore species that occurs on rocky or rubble reef, and by
day has a preference for caves. It is found at 5 – 30 m depth
(Heemstra, 1995). Though not typically reported in the diet
of spinner dolphins, apogonids have been found in their
stomach contents by studies elsewhere (Perrin & Gilpatrick,
Fitch & Brownell (1968) suggested that spinner dolphins
feed at depths greater than 250 m. Dolar et al. (2003) hypoth-
esized that this species may feed as deep as 400 m. However,
spinner dolphins in the Philippines were observed feeding
near the surface at night (Dolar et al., 2003). The high
density of myctophids near the surface at night in the Sea of
Oman (Gjøsaeter, 1984; Valinassab et al., 2007) coupled
with their high abundance in the dolphins’ stomachs suggest
that the spinner dolphins examined here are likely to have
fed mainly in the epipelagic layer at night. Although spinner
dolphins were observed frequently in association with
schools of feeding yellowﬁn tuna (Thunnus albacares) in the
day during detailed behavioural studies off Muscat, feeding
was rarely observed (only 3% of total observation time)
The diet of spinner dolphins has been studied extensively
in the Eastern Tropical Paciﬁc (ETP) and in the Hawaiian
archipelago. Fitch & Brownell (1968) examined the stomachs
of ﬁve spinner dolphins caught in the ETP and found a mainly
piscivorous diet comprising 6 – 15 species in eight families,
whereby the myctophids B. panamense and Lampanyctus par-
vicauda constituted 50% of the dolphins’ diet. Squid predomi-
nated in the stomach contents of a single dolphin caught in
Hawai’i, although there were also ﬁsh from the families
Gempylidae and Myctophidae (Shomura & Hida, 1965).
Dolar et al. (2003) examined the stomachs of 45 spinner dol-
phins that had been caught in the tuna driftnet ﬁshery in the
Sulu Sea and found that myctophids formed the basis of the
dolphins’ diet (32 species, 94% in occurrence), with three
species dominating. Furthermore, 10 families of mesopelagic
cephalopods, dominated by the family Enoploteuthidae, and
crustaceans from three families (Oplophoridae, Penaeidae
and Sergestidae) were also found in the stomachs (Dolar
et al., 2003).
The stomach contents of the Oman spinner dolphins had a
much lower diversity (ﬁve ﬁsh and one cephalopod species)
than those in the ETP and the Philippines. However, as in
the Sulu Sea, Hawai’i and ETP, mesopelagic ﬁsh, particularly
myctophids dominated the stomach contents. The genus
Benthosema was important for both ETP dolphins and the
ones in this study, while the squid O. banksi was a prey
item of both Sulu Sea spinner dolphins and the spinner dol-
phins from this study. In contrast, in two separate studies in
India, examination of the stomach contents of two spinner
dolphins caught incidentally in gill nets revealed that one
animal had mainly consumed the epipelagic scad mackerel
Megalaspis cordyla (Karbhari et al., 1985), while the other
had mostly taken shallow water pandalid prawns and the
squid Loligo duvaucelli (Natarajan & Rajaguru, 1985), while
in yet another study in India, a spinner dolphin caught inci-
dentally was found to have consumed mainly the shrimp
Solenocera crassicornis, also found in shallow water
(Krishnan et al., 2007). Two possible reasons for the low diver-
sity in the stomach contents examined here are the extremely
small sample size, lacking representation from what could be a
larger prey spectrum and/or over-representation of a single
species of mesopelagic ﬁsh (B. pterotum) in the Sea of
Oman (Gjøsaeter 1984; Valinassab et al., 2007).
Commercial importance of prey species
Of the 22 prey species found in the stomachs of bottlenose
dolphins, only a few are of major commercial importance in
Oman, being targeted either by traditional or industrial
ﬁshers, or both (Al-Abdessalaam, 1995). Apogonidae, the
most important prey family numerically for bottlenose dol-
phins has no commercial value in Oman (Al-Abdessalaam,
1995). Otolithes ruber, important to both bottlenose and
Indo-Paciﬁc humpback dolphins, contributes signiﬁcantly to
the overall croaker ﬁshery in Oman (Al-Abdessalaam, 1995;
Ministry of National Economy, 2007). In 1995, trichiurids
ranked among the top ﬁve families in the Omani demersal
ﬁsh catch, along with sciaenids, siganids, serranids and lethri-
nids (Siddeek et al., 1999). Arius spp., consumed by
Indo-Paciﬁc humpback dolphins, is caught commercially in
bottom trawlers, although not highly valued as a food ﬁsh in
Oman, and thus are mostly discarded due to the lack of
local demand (Al-Abdessalaam, 1995). Mesopelagic species
in the Sea of Oman, particularly the dominant Benthosema
pterotum, remain a largely unexploited ﬁsheries resource,
thus providing the potential for developing a ﬁshery for ﬁsh-
meal (Gjøsaeter, 1984; Johannesson, 1995). Al-Marzooqi
1706 louisa s. ponnampalam et al.
(2001) reported that the abundance of myctophids in the Gulf
of Oman and Arabian Sea has sparked interest in developing a
ﬁshmeal ﬁshery in the area. However, Valinassab et al. (2007)
reported that maximum yields of B. pterotum in the Sea of
Oman, which undergo seasonal ﬂuctuations, would not be
adequate for sustaining the ﬁshery. More research is needed
on the consumption biomass of spinner dolphins in Oman
to be able to discern whether a myctophid ﬁshery would
have impacts on their feeding ecology.
As discussed above, small sample sizes may lead to biases
associated with lack of the full range of prey species or over-
representation of species comprising the last few meals of
the few animals examined. Further limitations pertaining to
this dataset include the lack of availability of relevant allo-
metric coefﬁcients to conduct length and weight regressions.
This prevented percentage by weight (%W) and passage
time analyses. Additionally, the identiﬁcation of cephalopod
beaks may not be entirely accurate for several reasons.
Firstly, all published references for Oman, including those of
the Ministry of Agriculture and Fisheries (currently known
as Ministry of Agriculture and Fisheries Wealth) indicate
that Sepia pharaonis and Octopus aegina are the only cephalo-
pod species to occur in Oman. Published information on
cephalopod diversity for the wider region is also scant and
there was no readily available reference collection of beaks
or a suitable beak identiﬁcation key for Oman or surrounding
Possible sources of bias in the data
There are biases associated with studying diet based on
stomach contents of beach-cast cetaceans. For example, the
dolphins in this study were found in varying states of
decomposition and with varying states of stomach fullness.
Their causes of mortality could not always be determined,
and in some cases might have been due to illness or
by-catch. If the samples had come from sick individuals,
samples used here may not be completely reﬂective of a
normal diet in a healthy dolphin. In the case of by-catch, dol-
phins are sometimes known to regurgitate some or all of their
stomach contents upon capture or entanglement in the ﬁshing
gear, perhaps due to stress (e.g. Sekiguchi et al., 1992;
Krishnan et al., 2007). If some of the stomachs studied here
were from by-caught dolphins, then the results may also not
be truly representative of their actual diet, as they may have
been feeding opportunistically near ﬁshing vessels or off
ﬁshing gear prior to incidental capture. There are also biases
associated with the digestibility of prey items. For instance,
larger and denser ﬁsh otoliths tend to be retained intact for
longer than smaller otoliths (Murie & Lavigne, 1985), due to
their differing rates of erosion (Jobling & Breiby, 1986). It is
thus possible that the results here over-represent ﬁsh species
with larger otoliths and under-represent ﬁsh species with
smaller and more fragile otoliths. It also does not necessarily
indicate that all prey species found in each stomach were
taken in a single meal. Another bias resulting from stomach
contents analysis is the longer retention of cephalopod beaks
within the stomach compared with ﬁsh otoliths (Heezik &
Seddon, 1989). However, this bias is likely not to have affected
the results here as most samples examined in this study con-
tained more otoliths than beaks. Some of the prey remains
found could have been secondary prey items (i.e. prey
consumed by the dolphin’s prey), thus potentially biasing
results. Additionally, due to small sample size and lack of
life history data for examined specimens, it was not possible
to examine the diet and prey selection of each dolphin
based on sex, maturity or seasonality. Several studies have
found dietary differences at varying stages of maturity and
life history due to demographic differences in habitat selection
and/or ontogenetic changes in prey choice, between sexes and
between seasons (Robertson & Chivers, 1997; Amir et al.,
2005; Santos et al., 2007).
While the stomach contents data indicate that bottlenose dol-
phins and Indo-Paciﬁc humpback dolphins in the Gulf of
Masirah are feeding in overlapping habitats, the results also
indicated that the two species have different prey spectra
with only minor overlaps in species consumed. Spinner dol-
phins were more speciﬁc in their prey choice and were able
to exploit what appears to be an abundant food resource
from the vertically migrating mesopelagic deep-scattering
layer. Only a small percentage of the three dolphin species’
prey items are of current commercial importance, indicating
that there is little direct competition with local ﬁsheries.
However, a number of animals examined in this study
showed signs of mortality due to ﬁsheries interaction, indicat-
ing that these dolphins still face a signiﬁcant risk of incidental
capture from feeding in the same highly productive areas
where ﬁshing occurs. Despite the limitations of this study,
the data presented here remain important in furthering our
understanding of the ecology of small cetaceans in this
region and for designing future studies on this subject.
This work was supported by an Association of
Commonwealth Universities (ACU) doctoral scholarship
granted to L.S.P. We are very grateful to the Government of
Oman, in particular, the former Ministry of Regional
Municipalities, Environment and Water Resources (now
known as the Ministry of Environment and Climate
Affairs), the former Ministry of Agriculture and Fisheries
(now known as the Ministry of Agriculture and Fisheries
Wealth), and the Oman Natural History Museum of the
Ministry of Heritage and Culture for granting us permission
to conduct our research. Thanks are also owed to the Board
Members of the Environment Society of Oman and personnel
at Five Oceans Environmental Services in Oman for their
support. Our gratitude is also extended to the many volunteers
who gave assistance during beach surveys, and in the proces-
sing of the stomach contents samples—Vic Cockcroft, Anna
Hywel-Davies, Fergus Kennedy, Andy Willson, Simon
Wilson, Kris Vallancey, Richard Willing, Natalie Little,
Robyn Manley, Eli Verges-Vidal, Louise Waters, Ross
Rosenquist, Cathy Little, Rebecca Lovegrove, Victoria Hill
and Rebekah Oxley. We would like to express our appreci-
ation to Dr Begon
˜a Santos, Dr Stephanie Plo
¨n and Dr
Kenneth Longenecker for their kind assistance in identifying
cephalopod beaks and ﬁsh dentary bones. Surveys would
not have been possible without the funding provided by
Shell Oman Marketing, Ford Environmental Grants,
stomach contents of cetaceans in oman 1707
Petroleum Development Oman, the UK Foreign and
Commonwealth Ofﬁce, Veritas Geophysical, the Peter Scott
Trust for Education and Research in Conservation, Salalah
Port Services, DHL Worldwide Express, Truck Oman,
Oman Air, the Wildlife Conservation Society, Muscat
Pharmacy, KPMG, Han-Padron and Associates, Five Oceans
Environmental Services and the Marina Bandar Al Rowdah.
Last but not least, we would like to thank Anouk
Ilangakoon and the four anonymous referees for reviewing
and improving an earlier version of this manuscript.
Al-Abdessalaam T.Z.S. (1995) Marine species of the Sultanate of Oman.
Ministry of Agriculture and Fisheries, Sultanate of Oman.
Al-Marzooqi A.S. (2001) Feasibility study of the mesopelagic (myctophids)
commercial ﬁshery in the Gulf of Oman. MSc thesis. University of Hull,
Amir O.A., Berggren P., Ndaro S.G.M. and Jiddawi N.S. (2005) Feeding
ecology of the Indo-Paciﬁc bottlenose dolphin (Tursiops aduncus)
incidentally caught in the gillnet ﬁsheries off Zanzibar, Tanzania.
Estuarine, Coastal and Shelf Science 63, 429–437.
Baldwin R. (2003) Whales and dolphins of Arabia. Muscat: Mazoon
Printing Press L.L.C.
Baldwin R.M., Van Waerebeek K. and Gallagher M. (1998) A review of
small cetaceans from waters off the Arabian Peninsula. Document SC/
50/SM6 presented at the 50th meeting of the International Whaling
Commission, 26 pp.
Baldwin R.M., Collins T., Van Waerebeek K. and Minton G. (2004) The
Indo-Paciﬁc humpback dolphin of the Arabian region: a status review.
Aquatic Mammals 30, 111–124.
Banzon V.F., Evans R.E., Gordon H.R. and Chomko R.M. (2004)
SeaWiFS observations of the Arabian Sea southwest monsoon bloom
for the year 2000. Deep-Sea Research Part II: Topical Studies in
Oceanography 51, 189– 208.
Barros N.B. and Wells R.S. (1998) Prey and feeding patterns of resident
bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida.
Journal of Mammalogy 79, 1045–1059.
Barros N.B., Jefferson T.A. and Parsons E.C.M. (2004) Feeding habits of
Indo-Paciﬁc humpback dolphins (Sousa chinensis) stranded in Hong
Kong. Aquatic Mammals 30, 179–188.
Barros N.B., Parsons E.C.M. and Jefferson T.A. (2000) Prey of offshore
bottlenose dolphins from the South China Sea. Aquatic Mammals 26,
Benoit-Bird K.J. (2004) Prey calorie value and predator energy needs:
foraging predictions for wild spinner dolphins. Marine Biology 145,
Bowen W.D. and Siniff D.R. (1999) Distribution, population biology,
and feeding ecology of marine mammals. In Reynolds J.E. and
Rommel S.A. (eds) Biology of marine mammals. Washington, DC:
Smithsonian Institution Press, pp. 423–484.
Butler J.L. (1979) The nomeid genus Cubiceps (Pisces) with a description
of a new species. Bulletin of Marine Science 29, 226 – 241.
Clarke M. (1986) Handbook for the identiﬁcation of cephalopod beaks.
Oxford: Oxford University Press.
Clarke T.A. (1973) Some aspects of the ecology of lanternﬁshes
(Myctophidae) in the Paciﬁc Ocean near Hawaii. Fishery Bulletin 71,
Dalpadado P. and Gjøsaeter J. (1988) Feeding ecology of the lanternﬁsh
Benthosema pterotum from the Indian Ocean. Marine Biology 99,
Di Beneditto A.P.M. and Siciliano S. (2007) Stomach contents of the
marine tucuxi dolphin (Sotalia guianensis) from Rio de Janeiro, south-
eastern Brazil. Journal of the Marine Biological Association of the
United Kingdom 87, 253–254.
Dolar M.L.L., Walker W.A., Kooyman G.L. and Perrin W.F. (2003)
Comparative feeding ecology of spinner dolphins (Stenella longirostris)
and Fraser’s dolphins (Lagenodelphis hosei) in the Sulu Sea. Marine
Mammal Science 19, 1–19.
Findlay K.P., Best P.B., Ross G.J.B. and Cockcroft V. (1992) The distri-
bution of small odontocete cetaceans off the coasts of South Africa and
Namibia. South African Journal of Marine Science 12, 237 –270.
Fitch J.E. and Brownell R.L. Jr (1968) Fish otoliths in cetacean stomachs
and their importance in interpreting feeding habits. Journal of the
Fisheries Research Board of Canada 25, 2561–2574.
Geraci J.R. and Lounsbury V.J. (2005) Marine mammals ashore: a ﬁeld
guide for strandings. 2nd edition. Baltimore, MD: National
Aquarium in Baltimore.
Gjøsaeter J. (1984) Mesopelagic ﬁsh, a large potential resource in the
Arabian Sea. Deep- Sea Research Part I 31, 1019–1035.
Heemstra P.C. (1995) Additions and corrections for the 1995 impression.
In Smith M.M. and Heemstra P.C. (eds) Revised edition of Smiths’ sea
ﬁshes. Berlin: Springer-Verlag, pp. 5– 15.
Heezik Y.V. and Seddon P. (1989) Stomach sampling in the Yellow-eyed
Penguin: erosion of otoliths and squid beaks. Journal of Field
Ornithology 60, 451–458.
Hui C.A. (1985) Undersea topography and the comparative distributions
of two pelagic cetaceans. Fishery Bulletin 83, 472–475.
Hyslop E.J. (1980) Stomach contents analysis–a review of methods and
their application. Journal of Fish Biology 17, 411–429.
Jefferson T.A. (2000) Population biology of the Indo-Paciﬁc hump-
backed dolphin in Hong Kong waters. Wildlife Monographs 144, 1– 65.
Jereb P. and Roper C.F.E. (2005) Cephalopods of the world. An annotated
and illustrated catalogue of cephalopod species known to date. Volume
1. Chambered nautiluses and sepioids (Nautilidae, Sepiidae, Sepiolidae,
Sepiadariidae, Idiosepiidae and Spirulidae). FAO Species Catalogue for
Fishery Purposes, No. 4, Volume 1, 262 pp.
Jobling M. and Breiby A. (1986) The use and abuse of ﬁsh otoliths in
studies of feeding habits of marine piscivores. Sarsia 71, 265– 274.
Johannesson K.A. (1995) Assessment of major marine ﬁsh stocks of demer-
sal, small pelagic and mesopelagic species. Oman. R/V RASTRELLIGER
acoustic & trawling survey results (November 1989–November 1990).
FAO/UNDP Project for ﬁsheries resources assessment survey,
Muscat, Oman. Technical Report FI-DP/OMA/88/005, 226 pp.
Karbhari J.P., Aravindakshan M., Wagmare K.B. and Gandhi R. (1985)
Note on the food of the spinner dolphin Stenella longirostris Gray,
caught off Maharashtra coast. Journal of the Marine Biological
Association of India 27, 193–195.
Krishnan A.A., Yousuf K.S., Kumaran P.L., Harish N., Anoop B., Afsal
V.V., Rajagopalan M., Vivekanandan E., Krishnakumar P.K. and
Jayasankar P. (2007) Stomach contents of cetaceans incidentally
caught along Mangalore and Chennai coasts of India. Estuarine,
Coastal and Shelf Science 76, 909–913.
Krishnapillai S. and Kasinathan C. (1987) Some observations on dol-
phins in Mandapam area with a note on their food. Marine Fisheries
Information Service Technical and Extension Series 71, 13 – 16.
Kubodera T. (2005) Manual for the identiﬁcation of cephalopod beaks in
the Northwest Paciﬁc. For researchers on feeding habits of marine
1708 louisa s. ponnampalam et al.
mammals, seabirds and ﬁshes. Version 1-1. Available online at http://
research.kahaku.go.jp/zoology/Beak-E/index.htm (accessed 19
Lahaye V., Bustamante P., Spitz J., Dabin W., Das K., Pierce G.J. and
Caurant F. (2005) Long-term dietary segregation of common dolphins
Delphinus delphis in the Bay of Biscay, determined using cadmium as
an ecological tracer. Marine Ecology Progress Series 305, 275–285.
McClatchie S. and Dunford A. (2003) Estimated biomass of vertically
migrating mesopelagic ﬁsh off New Zealand. Deep-Sea Research Part
I: Oceanographic Research Papers 50, 1263 –1281.
Ministry of National Economy (2007) Statistical Yearbook 2007. Volume
35. Available online at http://www.moneoman.gov.om/book/
syb2008cd/english.html (accessed 19 October 2011).
Minton G., Collins T., Findlay K. and Baldwin R. (2010) Cetacean dis-
tribution in the coastal waters of the Sultanate of Oman. Journal of
Cetacean Research and Management 11, 301–313.
Murie D.J. and Lavigne D.M. (1985) Digestion and retention of Atlantic
herring otoliths in the stomachs of grey seals. In Beddington J.R.,
Beverton R.J.H. and Lavigne D.M. (eds) Marine mammals and ﬁsh-
eries. London: George Allen & Unwin, pp. 292 –299.
Nakamura I. and Parin N.V. (1993) FAO species catalogue. Volume 15.
Snake mackerels and cutlassﬁshes of the world (Families Gempylidae
and Trichiuridae). An annotated and illustrated catalogue of the
snake mackerels, snoeks, escolars, gemﬁshes, sackﬁshes, domine,
oilﬁsh, cutlassﬁshes, scabbardﬁshes, hairtails, and frostﬁshes known to
date. FAO Fisheries Synopsis, No. 125, Volume 15, 136 pp.
Natarajan R. and Rajaguru A. (1983) Food and feeding habits of Stenella
longirostris and Tursiops truncatus (Cetacea) off Porto-Novo, east
coast of India. In Abstracts Fifth Biennial Conference on the Biology
of Marine Mammals, November 27 –December 1, 1983, Boston,
Natarajan R. and Rajaguru A. (1985) Small cetaceans. Marine Mammal
Science 1, 89.
Nelson J.S. (1994) Fishes of the world. New York: John Wiley and Sons
˜o-Torres C.A., Gallo-Reynoso J.P., Galvan-Magana F.,
Escobar-Briones E. and Macko S.A. (2006) Isotopic analysis of C
, and S
‘A feeding tale’ in teeth of the longbeaked common
dolphin, Delphinus capensis.Marine Mammal Science 22, 831– 846.
Paxton J.R. and Hulley P.A. (1999) Myctophidae. Lanternﬁshes. In
Carpenter K.E. and Niem V.H. (eds) FAO species identiﬁcation guide
for ﬁshery purposes. The living marine resources of the WCP. Volume
3. Batoid ﬁshes, chimaeras and bony ﬁshes part 1 (Elopidae to
Linophrynidae). Rome: FAO, pp. 1957–1964.
Perrin W.F. and Gilpatrick J.W. (1994) Spinner dolphin Stenella longir-
ostris (Gray, 1828). In Ridgway S.H. and Harrison R. (eds) Handbook
of marine mammals. London: Academic Press, pp. 99–128.
Pinkas L., Oliphant M.S. and Iverson I.L.K. (1971) Food habits of alba-
core, blueﬁn tuna and bonito in California waters. Fishery Bulletin 152,
Ponnampalam L.S. (2009) Ecological studies and conservation of small
cetaceans in the Sultanate of Oman, with special reference to spinner
dolphins, Stenella longirostris (Gray,1828). PhD thesis. University
Marine Biological Station Millport (University of London), Scotland,
Randall J.E. (1995) Coastal ﬁshes of Oman. Bathurst, NSW: Crawford
House Publishing Pty. Ltd.
Robertson K.M. and Chivers S.J. (1997) Prey occurrence in pantropical
spotted dolphins, Stenella attenuata, from the eastern tropical Paciﬁc.
Fishery Bulletin 95, 334–348.
Robineau D. and Fiquet P. (1994) The Cetacea of the Jubail Marine
Wildlife Sanctuary, Saudi Arabia. In Krupp F., Abuzinada A.H. and
Nader I.A. (eds) A marine wildlife sanctuary for the Arabian Gulf
environmental research and conservation following the 1991 Gulf
War oil spill. Riyadh, Saudi Arabia: National Commission for
Wildlife Conservation and Development, pp. 438–458.
Robison B.H. and Craddock J.E. (1983) Mesopelagic ﬁshes consumed by
Fraser’s dolphin, Lagenodelphis hosei. Fishery Bulletin 81, 283–289.
Sætersdal G., Bianchi G., Strømme T. and Venema S.C. (1999) The DR
FRIDTJOF NANSEN Programme 1975– 1993. Investigations of ﬁshery
resources in developing countries. History of the programme and
review of results. FAO Fisheries Technical Paper, No. 391, 434 pp.
Salm R.V. (1991) Live and beached cetacean observations, Sultanate of
Oman. Scientiﬁc Results of the IUCN Coastal Zone Management
Santos M.B., Fernandez R., Lopez A., Martinez J.A. and Pierce G.J.
(2007) Variability in the diet of bottlenose dolphin, Tursiops truncatus,
in Galician waters, north-western Spain, 1990 – 2005. Journal of the
Marine Biological Association of the United Kingdom 87, 231 – 241.
Sasaki K. (2001) Sciaenidae. Croakers (drums). In Carpenter K.E. and
Niem V.H. (eds) FAO species identiﬁcation guide for ﬁshery purposes.
The living marine resources of the Western Central Paciﬁc. Volume 5.
Bony ﬁshes part 3 (Menidae to Pomacentridae). Rome: FAO, pp.
Sekiguchi K. (1995) Occurrence, behavior and feeding habits of harbor
porpoises (Phocoena phocoena) at Pajaro Dunes, Monterey Bay,
California. Aquatic Mammals 21, 91– 103.
Sekiguchi K., Klages N.T.W. and Best P.B. (1992) Comparative analysis
of the diets of smaller odontocete cetaceans along the coast of southern
Africa. South African Journal of Marine Science 12, 843 –861.
Selzer L.A. and Payne P.M. (1988) The distribution of white-sided
(Lagenorhynchus acutus) and common dolphins (Delphinus delphis)
vs. environmental features of the continental shelf of the northeastern
United States. Marine Mammal Science 4, 141– 153.
Shomura R.S. and Hida T.S. (1965) Stomach contents of a dolphin
caught in Hawaiian waters. Journal of Mammalogy 46, 500 –501.
Siddeek M.S.M., Fouda M.M. and Hermosa G.V. Jr (1999) Demersal
ﬁsheries of the Arabian Sea, the Gulf of Oman and the Arabian
Gulf. Estuarine, Coastal and Shelf Science 49, 87–97.
Silas E.G., Nammalwar P. and Sarvesan R. (1985) On the food of sperm
whale Physeter macrocephalus (Linnaeus 1758) at Tranquebar with a
note on the food habits of sperm whales. In Proceedings of the
Symposium on Endangered Marine Animals and Marine Parks 1985,
Marine Biological Association of India 1, pp. 65–71.
Silver M.W. (1975) The habitat of Salpa fusiformis in the California
Current as deﬁned by indicator assemblages. Limnology and
Oceanography 20, 230– 237.
Smale M.J., Watson G. and Hecht T. (1995) Otolith atlas of southern
African marine ﬁshes. Ichthyological Monographs No. 1.
Grahamstown, South Africa: J.L.B. Smith Institute of Ichthyology.
Smith M.M. and Heemstra P.C. (1986) Smith’s sea ﬁshes. Grahamstown,
South Africa: J.L.B. Smith Institute of Ichthyology.
Smith S.C. and Whitehead H. (2000) The diet of Gala
´pagos sperm whales
Physeter macrocephalus as indicated by fecal sample analysis. Marine
Mammal Science 16, 315–325.
Valinassab T., Pierce G.J. and Johannesson K. (2007) Lantern ﬁsh
(Benthosema pterotum) resources as a target for commercial exploita-
tion in the Oman Sea. Journal of Applied Ichthyology 23, 573–577.
stomach contents of cetaceans in oman 1709
Walker W.A. (1981) Geographical variation in morphology and biology of
the bottlenose dolphins (Tursiops) in the eastern North Paciﬁc. NMFS/
SWFC Administrative Report, No. LJ-81-03C.
Wang W. (1995) Biology of Sousa chinensis in Xiamen Harbor. In Woo J.
and Liu W. (eds) Conference on conservation of marine mammals in
Fujian, Hongkong, and Taiwan. Speciﬁc publication of the Journal of
Oceanography of the Taiwan Strait 4, pp. 21–26. [In Chinese.]
Wang J.Y., Chou L.-S. and White B.N. (2000) Differences in the external
morphology of two sympatric species of bottlenose dolphins (Genus
Tursiops) in the waters of China. Journal of Mammalogy 81,
Wells R.S. and Scott M.D. (2002) Bottlenose dolphins. In Thewissen
J.G.M. (ed.) Encyclopedia of marine mammals. San Diego, CA:
Academic Press, pp. 122–128.
Correspondence should be addressed to:
Environment Society of Oman
PO Box 3955, P.C. 112, Ruwi, Sultanate of Oman
1710 louisa s. ponnampalam et al.