Robertson and Chivers: Prey of Stenella attenuate 
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1 = Myctophidae 
2 = Enoploteuthidae 
3 = Ommastrephidae 
4 = Cranchiidae 
5 = Nomeidae 
6 = Mastigoteuthidae 
7 = Onychoteuthidae 
8 = Bregmacerotidae 
9 = Phosichthydae 
10 = Melamphaidae 
11 = Exocoetidae 
12 = Pholidoteuthidae 
13 = Paralipididae 
14 = Thysanoteuthidae 
15 = Octopoteuthidae 
16 = Ctenopterygidae 
17 = Notosudidae 
18 = Scombridae 
19 = Acropomatidae 
■ Specimen 
□ Set 
Prey families 
Figure 5 
Percent number for each prey family calculated by using set as the sampling unit and each specimen as 
the sampling unit. Only those prey families with a percent number >0.100 are shown. 
using each set as a sampling unit. The percent num- 
bers, for set as the sampling unit and specimen as 
the sampling unit, were then compared by using a 
Mann-Whitney rank test, and no significant differ- 
ence was found in the rank order of prey families 
between the set and specimen methods (Zar, 1984, 
p. 141-143; P= 0.05, Fig. 5). Therefore, we conclude that 
for our data set, there was no bias introduced by using 
multiple specimens collected from the same set. 
Summary 
Based on the analysis and identification of fish 
otoliths and cephalopod beaks, our results provide 
evidence that pantropical spotted dolphins feed pri- 
marily at night on mesopelagic fish and squid. The 
dominant prey species belong to the families 
Myctophidae, Enoploteuthidae, and Ommastrephi- 
dae. Composition of the diet differed by season and 
area; thus pantropical spotted dolphins are likely op- 
portunistic feeders. Prey included a wide range of 
sizes of both fish and squid, with the largest prey 
consumed by the largest dolphins, and the smallest 
prey consumed in the largest numbers. Furthermore, 
the diet of female dolphins differed by reproductive 
condition. Lactating females consumed more food and 
a higher proportion of squid than did pregnant 
females. 
Acknowledgments 
We would like to thank the biological technicians 
(NMFS, Southwest Region) who collected the stom- 
achs for this study, F. G. Hochberg for assistance in 
identifying the cephalopod beaks (Santa Barbara 
Museum of Natural History), R. Lavenberg for the 
use of the otolith reference collection at the Los An- 
geles County Museum of Natural History, and R. 
Lindsey ( Inter- American Tropical Tuna Commission 
[IATTC]) and R. Rassmussen (Southwest Fisheries 
Science Center [SWFSC]) for time-of-day data. We 
would also like to thank J. Carretta and R. Pitman 
(SWFSC) for their assistance with identifying 
myctophid and flying fish otoliths. We are grateful 
to M. Henshaw (SWFSC), W. F. Perrin (SWFSC), R. 
Olson (IATTC), M. Scott (IATTC), and two anony- 
mous reviewers for their helpful comments and me- 
ticulous reviews of the manuscript. 
