Kane et al. : Prevalence of Xenobalanus globiclpitis on cetacean species in the eastern tropical Pacific Ocean 
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eastern tropical 
Pacific Ocean (ETP) 
Figure 2 
Documented sightings of Xenobalanus worldwide on various cetacean hosts compiled from lit- 
erature review, and an outline of the current study area (eastern tropical Pacific Ocean). Ovals 
indicate the geographic region where barnacles have been reported and their size does not indicate 
intensity of infestation. Refer to Table 3 for the corresponding citations for each region. 
tation, were used. Photographs used represent a sub- 
sample of individuals and did not include every animal 
observed. Killer whales ( Orcinus orca) were studied 
in additional detail, by using photographs taken on 
previous cruises dating back to 1977, and including 
photographs from the ETP in the California and Mexico 
killer whale catalog (Black et al., 1997). 
Data analysis 
Two measures of prevalence of Xenobalanus were calcu- 
lated for each cetacean species with at least three sight- 
ings with usable photographs. Prevalence was calculated 
for each sighting by dividing the number of individual 
whales or dolphins with barnacles by the total number 
of individual cetaceans identified. Mean prevalence and 
its standard error for each species were calculated from 
these values. Prevalence per sighting was calculated for 
each species by dividing the number of sightings with 
barnacles present by the total number of sightings. Mean 
barnacle intensity was calculated as the total number 
of barnacles observed on a host species divided by the 
number of infested hosts of the same species (Bush 
et al., 1997). To relate barnacle presence to primary 
productivity, the presence or absence of Xenobalanus at 
each cetacean sighting in 2003 was plotted on a map of 
average surface chlorophyll concentration in the ETP 
that was based on data provided by the SeaWiFS Project, 
NASA/Goddard Space Flight Center, and GeoEye. 
Several statistical tests were performed to determine 
significant differences among the data. A nonparamet- 
ric Mann Whitney-G test was used to determine if the 
rates of prevalence differed between Mysticetes and 
Odontocetes and a nonparametric Kruskal-Wallace test 
was used to determine if the prevalence rates differed 
significantly among species. Chi-square goodness-of-fit 
test was used to determine if the number of barnacles 
per killer whale followed a Poisson distribution. After 
normalization, linear regression was used to determine 
if the number of barnacles observed was predicted by 
the total number of animals observed in the sighting. 
Results 
Within the ETP over 10,000 photographs of 22 cetacean 
species and 2510 individuals revealed that 132 individu- 
als of 14 species were host to Xenobalanus (Table 1). Out 
of 497 photographed sightings, 445 were determined 
to be usable in the analysis, and of these sightings, 47 
displayed Xenobalanus: 38 odontocete sightings and 
9 mysticete sightings. Xenobalanus was not observed 
on seven cetacean species and on one genus for which 
the species could not be identified: pygmy killer whale 
