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Fishery Bulletin 106(4) 
Xenobalanus presence or absence for 445 cetacean sightings in the eastern tropical Pacific Ocean (ETP) in 2003 as 
determined from analysis of identification photographs. Dots (•) indicate cetacean sightings with no Xenobalanus 
observed; circles (O) indicate sightings with one or more barnacles observed; the solid line indicates the border of 
the ETP study area. Presence or absence is overlaid on a background of graded shading representing the volume of 
chlorophyll-a (mg/m 3 ) averaged from September to November 2003. 
Materials and methods 
Data collection 
Cetaceans were photographed during a 2-ship, 4-month 
research cruise in 2003, covering 26,000 km of tran- 
sects surveyed for marine mammals (boundaries shown 
in Figs. 1 and 2). Camera equipment included Canon 
EOS 10D and D60 digital cameras (Canon USA, Lake 
Success, NY) with 75-300 mm image-stabilized zoom 
and 400-mm fixed lenses. Date, latitude and longitude, 
cetacean species (as identified by trained cruise person- 
nel), and unique sighting number per cetacean group 
were recorded with each photograph. In the laboratory, 
additional data were recorded upon examination of pho- 
tographs, including the number of usable photographs in 
the sighting (as described below), number of individual 
cetaceans identified in the sighting, number of individu- 
als infested with Xenobalanus, and number of Xenobala- 
nus present. If barnacles were clumped in such a way 
as to compromise the accuracy of the count, the maxi- 
mum number of discernible barnacles was recorded. The 
resolution of the digital photographs was such that in 
most cases, individual barnacles were easily identified. 
In external appearance, Xenobalanus may be confused 
with the parasitic copepod Pennella balaenoptera (Ev- 
ans, 1994) or the stalked barnacle Conchoderma virga- 
tum (Ruppert et al., 2004). However, the much larger P. 
balaenoptera usually occurs along the flanks, whereas 
Xenobalanus is generally found along the trailing edges 
of the dorsal fin, pectoral flippers, and the fluke, as has 
been described for stranded and live cetaceans. Similar 
to P. balaenoptera, C. virgatum requires a less specific 
position for attachment, requiring any hard substrate 
(such as another barnacle, a tooth, or exposed bone), and 
C. virgatum is considerably lighter in coloration than 
Xenobalanus. Digital photographic quality was sufficient 
for accurate identification of the commensal Xenobala- 
nus-, no specimens were obtained for direct examination. 
During the cruise, typically many photographs were 
taken for each sighting. For our study, usable photo- 
graphs had 1) to be in focus, 2) to be of sufficient resolu- 
tion to identify a barnacle if present, and 3) to include 
at least one cetacean dorsal fin. For large schools, only 
one photograph per school was used in order to prevent 
recounting individuals. For small schools, only photo- 
graphs of animals identifiable as individuals, either 
from field notes or from unique markings or pigmen- 
