140 
Fishery Bulletin 115(2) 
not smaller than those of the other medium delphinids 
(Table 3). 
In a multispecies assessment of odontocetes in Ha¬ 
waii that was based on small-boat surveys, Baird et al. 
(2013) found that measures reflecting the detectability 
of rough-toothed dolphins (i.e., mean group size, mean 
distance when first sighted, and sightings per unit of 
effort) were nearly identical to those for bottlenose dol¬ 
phins, and individuals of both species are frequently 
sighted around the main Hawaiian Islands. Resighting 
rates of individual rough-toothed dolphins were high 
enough to indicate that island-associated populations 
are not exceptionally large (Baird et ah, 2008). The re¬ 
sults from Baird et ai. (2008) pertain to island-associ¬ 
ated populations, but Barlow (2006) estimated that the 
density of rough-toothed dolphins was approximately 
2.5 times higher within 140 km of the main Hawaiian 
Islands than throughout the rest of the Hawaiian Is¬ 
lands EEZ. Therefore, there are no available quantita¬ 
tive measures that would indicate that rough-toothed 
dolphins are particularly more difficult to see than in¬ 
dividuals of other species or have especially high abun¬ 
dance in the Hawaiian Islands EEZ. Further, rough- 
toothed dolphins frequently associate with individuals 
of other species and are generally not known to avoid 
vessels (Baird et al., 2008). Hence, a source of negative 
bias in the giO) estimates of Barlow (2015) for rough- 
toothed dolphins is not obvious. 
Rough-toothed dolphins were used as a case study 
in an evaluation of the use of passive acoustics as an 
independent detection platform for observers in the 
eastern tropical Pacific (Rankin et al.®). That study 
estimated that a majority of groups of rough-toothed 
dolphins were missed on the trackline. Because ad¬ 
ditional species were not assessed, it is unclear how 
often rough-toothed dolphins were missed in compari¬ 
son with individuals of other species. Overall, the low 
g(0) estimates and correspondingly high abundance 
estimates of rough-toothed dolphins in the Hawaiian 
Islands EEZ cannot be explained. 
As with the abundance estimates from the HICEAS 
in 2002 (Barlow, 2006), the precision of the estimates 
from the HICEAS in 2010 is generally poor (Table 3). 
For both sets of estimates, this imprecision is largely 
a result of the low number of sightings of most spe¬ 
cies. That is, these low numbers of sightings led to a 
high variance in each encounter rate that dominated 
the overall CV estimate (Barlow, 2006). However, the 
CVs of most estimates of abundance for 2010 are lower 
than the estimates for 2002, despite the addition of co¬ 
variate model selection and averaging in the bootstrap 
procedure used in the estimation for 2010. This slight 
increase in precision could be linked to the greater 
® Rankin, S., J. Barlow, J. Oswald, and T. Yack. 2009. A com¬ 
parison of the density of delphinids during a combined visual 
and acoustic shipboard line-transect survey [Abstract]. In 
1st international workshop on density estimation of marine 
mammals using passive acoustics; Pavia, Italy, 10-13 Sep¬ 
tember, p. 75. [Available at website, accessed May 2015.] 
number of sightings during the HICEAS in 2010. Sam¬ 
ple sizes for modeling the detection functions were gen¬ 
erally higher in the analysis for 2002 because pooled 
sightings from throughout the eastern North Pacific 
were used (Barlow, 2006). Although restricting the as¬ 
sessment for 2010 to sightings from the central North 
Pacific reduced available sample sizes for the estima¬ 
tion of detection functions, it likely reduced heteroge¬ 
neity that could not be accounted for by covariate test¬ 
ing and could have resulted in more precise abundance 
estimates for 2010. 
Cetaceans were sighted throughout the Hawaiian 
Islands EEZ (Fig. 1), but the distributions of sightings, 
by species, indicate areas of concentration for some 
species (Fig. 2). For example, sightings of pantropi- 
cal spotted dolphins were concentrated south of the 
main Hawaiian Islands, and sightings of sperm whales 
were concentrated in the northwestern portion of the 
Hawaiian Islands EEZ. The underlying distributions 
represent species-specific habitat associations and can 
vary temporally and spatially, leading to differences in 
species distributions between the HICEAS in 2002 and 
2010 (Forney et ai., 2015). These habitat associations 
were used to predict higher densities around the Ha¬ 
waiian Archipelago for several species, although not for 
all of them (Forney et al., 2015). 
Even with island-influenced productivity, the waters 
of the Hawaiian Islands EEZ are generally oligotro- 
phic—a condition that is reflected in the low density of 
cetaceans in the Hawiian Islands EEZ compared v/ith 
densities in areas with relatively high production (e.g., 
Wade and Gerrodette, 1993; Mullin and Fulling, 2004; 
Barlow and Forney, 2007). For example, total cetacean 
density in the eastern tropical Pacific was estimated 
to be 520 individuals/1000 km^ (Wade and Gerrodette, 
1993), and total cetacean density in the Southern Cali¬ 
fornia portion of the California Current ecosystem was 
estimated to be 678 individuals/1000 km^ (calculated 
from values given in Barlow and Forney, 2007). Both 
of those studies underestimated abundance by over¬ 
estimating g(0). Despite the application of the lower 
Beaufort-specific values of g(0) in the present study, 
total cetacean density was estimated to be only 146 
individuals/1000 km^. 
Approximately 93% of the estimated cetacean density 
for the HICEAS in 2010 consists of dolphin species. On 
the basis of sighting frequencies from small-boat sur¬ 
veys, Baird et al. (2013) suggested that the pantropical 
spotted dolphin was the most abundant cetacean spe¬ 
cies around the main Hawaiian Islands. In the broader 
Hawaiian Islands EEZ, the pantropical spotted dolphin 
was the thirdmost abundant species after the rough¬ 
toothed and striped dolphins (Table 3). The density of 
large whales (i.e., sperm and baleen whales) during the 
HICEAS in 2010 was about 2% of the total estimated 
cetacean density. The sperm whale was estimated to 
be the most abundant large whale species in the Ha¬ 
waiian Islands EEZ, although the estimated density of 
1.86 individuals/lOOO km^ for this species is just over 
half the density of sperm whales in the northeastern 
