402 
Fishery Bulletin 106(4) 
tal correlation in the distribution of Xenobalanus that 
is similar to that observed between primary production 
and barnacle presence in the ETP. Plankton abundance 
in oligotrophic areas of the ETP may be below a critical 
threshold for the filter-feeding barnacles and may thus 
indirectly limit the presence of Xenobalanus. 
The intensity of barnacles on killer whales in the ETP 
was not randomly distributed. There were more whales 
with no barnacles and with three or more barnacles 
than would be expected if barnacles settled randomly 
on killer whales, indicating that if Xenobalanus larvae 
settle, it is most often in groups of three or more. This 
aggregated or contagious distribution could occur as a 
result of: 1) a chemical cue emitted from the host that 
induces settlement (Nogata and Matsumura, 2005), 2) 
a chemical cue emitted from conspecifics that induces 
settlement (Knight- Jones, 1953), which was suggested 
for Xenobalanus by Aznar et al. (2005), 3) patchily dis- 
tributed barnacle larvae, or 4) an inability of the host 
to slough newly settled larvae (Ridgway et al., 1997). 
The low variance in prevalence and the nonuniform 
distribution of Xenobalanus sightings within the ETP 
indicate that most species are equally selected and 
that barnacle recruitment may be the result of patchily 
distributed larvae. 
Xenobalanus has been reported on a wide variety of 
cetacean hosts, and this apparent lack of specialization 
could provide insight into evolutionary age of Xenobala- 
nus. Various species of cyamid whale lice are highly 
specialized for a particular species of right whale ( Eu - 
balaena spp., Kaliszewska et al., 2005). Xenobalanus is 
more of a generalist than whale lice, given its apparent 
ability to settle on various cetacean hosts, which may 
indicate that its evolution and relationship with ceta- 
ceans may be more recent than that of other cetacean 
commensals, and that its specialization to host species 
has not yet occurred. Coronulid whale barnacles did 
not appear in the fossil record until approximately 23 
million years ago (Newman and Ross, 1976; Seilacher, 
2005), after the appearance of Mysticetes and Odon- 
tocetes in the fossil record approximately 35 million 
years ago. However, it is unknown at what point the 
genus Xenobalanus arose, and presently no data exist 
on the evolutionary age of cyamids for comparison. In 
the ETP, Xenobalanus, appearing on almost every ce- 
tacean species encountered, did not exhibit the degree 
of host specialization observed in whale lice. With a 
lack of data on evolutionary age, these findings support 
only the hypothesis that Xenobalanus is a generalist 
cetacean barnacle. 
Biological tags 
The relationship between commensals and their hosts, 
which can indicate host movement and host distribu- 
tional patterns, is often used to make inferences into the 
biology and ecology of the host. Comparison of internal 
parasite fauna has helped distinguish stocks, determine 
stock associations, track large-scale movements, and 
identify new recruits to populations in many species of 
fish, elasmobranchs, invertebrates, and marine mam- 
mals (Williams et ah, 1992). Among marine mammals, 
intestinal parasites, whale lice, and barnacles have 
proven useful for tracking migrations of gray whales 
(Eschrichtius robustus ; Killingley, 1980) and identifying 
stocks and the social structure of pilot whales (Globi- 
cephala melas; Balbuena and Raga, 1993), and have 
been useful for tracking general movement patterns of 
wide ranging, elusive cetacean populations without the 
use of expensive tagging equipment. 
Our results indicate that Xenobalanus, however, would 
not be useful as a biological tag. Within the ETP, Xe- 
nobalanus is widely distributed and a single, definitive 
source or home range was not determined for this spe- 
cies. However, this is the first study where distribution 
of Xenobalanus has been systematically examined on a 
large scale and it is possible that the few offshore obser- 
vations within the ETP are not representative of global 
distribution. Although Xenobalanus could not be used 
as a biological tag to track the movements of cetaceans 
within the ETP in this study, the potential use of Xe- 
nobalanus as a biological tag should not be abandoned 
completely. Increased knowledge of the biology of the 
barnacle, such as host-selection criteria, environmental 
tolerance limits, and early life history strategies could 
provide a finer resolution of the phoretic relationship 
with cetacean species that would enable the use of Xe- 
nobalanus as a biological tag in future studies. This 
and other research on Xenobalanus will form a useful 
part of the study of cetacean biology and ecology. 
Acknowledgments 
Funding for travel and living expenses for E. A. Kane 
was provided by the Evan Frankel Foundation. We thank 
J. Barlow, M. Kretzmann, and W. Perrin for reviewing 
the manuscript before submission, as well as D. Fertl 
and two anonymous reviewers for their helpful com- 
ments. We also thank N. Black and the many scientists 
and researchers who donated photographs, references, 
and information for the project. 
Literature cited 
Addink, M. J., and C. Smeenk. 
2001. Opportunistic feeding behavior of rough-toothed 
dolphins Steno bredanensis off Mauritania. Zool. Verh. 
(Leiden) 334:37-48. 
Aguilar, A., and J. A. Raga. 
1993. The striped dolphin epizootic in the Mediterranean 
Sea. Ambio 22:524-528. 
Aznar, F. J., D. Perdiguero, A. Perez del Olmo, A. Repulles, C. 
Agusti, and J. A. Raga. 
2005. Changes in epizoic crustacean infestations during 
cetacean die-offs: the mass mortality of Mediterranean 
striped dolphins Stenella coeruleoalba revisited. Dis. 
Aquat. Org. 67:239-247. 
Balhuena, J., and J. A. Raga. 
1989. Ecology and host relationships of the whale-louse 
