Byrd et at: Strandings as indicators of marine mammal biodiversity and human interactions 
19 
tached. Two of the stranded humpback whales showed 
evidence consistent with vessel strikes; one of these 
also had healed FI lesions (scars). 
Coastal bottlenose dolphins Within the diversity of 
strandings, the most common species by far was the 
coastal bottlenose dolphin, which resides in coastal and 
inshore waters and is present all year. Interpretation 
of spatiotemporal patterns is complicated, however, be- 
cause multiple stocks occur in NC waters, including at 
least 2 migratory coastal stocks and 2 resident estua- 
rine stocks (Waring et al., 2010). These multiple stocks 
add to the regional biodiversity and influence seasonal 
local abundance. All 4 stocks are susceptible to inciden- 
tal mortality in the myriad and seasonally changing 
commercial fisheries (Steve et al., 2001). 
Stranding patterns tended to echo the spatiotemporal 
occurrence of commercial gillnet fisheries, the principal 
source of known fisheries bycatch for coastal bottlenose 
dolphins off NC (Waring et al., 2010). The annual de- 
cline in nonperinatal HI-FI bottlenose dolphin strand- 
ings likely represents a real decrease in bycatch due, 
in part, to a series of regulations on gillnet fisheries 
since 2000 (Federal Register, 2006; Byrd et al., 2008). 
The monthly patterns of HI-FI strandings were similar 
to those of effort in the gillnet fishery, which is greatest 
in spring and fall and lowest in summer (Steve et al., 
2001). Although gill nets are used state-wide, the ocean 
fishery operates primarily from Oregon Inlet to Drum 
Inlet on the coast (from approximately ocean segments 
A2 to Bl) (NCDMF * * * * 7 ) and nearshore (0-5.6 km) (Palka 
and Rossman 8 ). The concentration of strandings just 
south of Cape Hatteras may indicate higher bycatch 
rates in that area due to either higher local abundance 
of dolphins (Torres et al., 2005), greater concentrations 
of gillnet effort, or both. In some cases, carcasses from 
north of Cape Hatteras may be entrained in waters 
that are driven south around the cape during strong 
northeast winds, which are more typical during winter 
months than other seasons (Gray and Cerame-Vivas, 
1963). Although overall seasonal effort in the inshore 
gillnet fishery is similar to that of the coastal fishery 
(Steve et al., 2001), the number of inshore strandings 
was too low to evaluate spatial effects. 
The close alignment of the patterns of HI-CBD with 
HI-FI strandings among years, months, and coastal 
segments, and the absence of similar patterns for Hl-no 
strandings, provides further evidence that a substan- 
' NCDMF (North Carolina Division of Marine Fisheries). 
2007. Assessment of North Carolina commercial finfisher- 
ies, 2004-2007. Final performance report for NMFS award 
number NA 04 NMF4070216, 380 p. [Available from NCD- 
MF, 3441 Arendell Street, Morehead City, NC 28557.1 
8 Palka, D. L., and M. C. Rossman. 2001. Bycatch estimates 
of coastal bottlenose dolphin (Tursiops truncatus) in U.S. mid- 
Atlantic gillnet fisheries for 1996-2000. U.S. Dep. of Com- 
mer., Northeast Fish. Sci. Cent. Ref. Doc. 01-15, 77 p. [Avail- 
able from 166 Water Street, Woods Hole, MA 02543-1026 or 
http://nefsc.noaa.gov/nefsc/publications/crd/crd0115/0115.pdf, 
accessed June 2012.] 
tial portion of HI-CBD strandings may indeed be HI- 
FI. More evidence comes from animals that were CBD 
for FI, but were mutilated similarly to those known to 
be positive for FI. In addition, physical processes, such 
as winds and currents, that resulted in the deposition 
of HI-FI or HI-CBD animals should have the same ef- 
fect on Hl-no strandings; therefore, those processes are 
not likely to be causing the difference between Hl-no 
and HI-CBD stranding patterns. 
Although there was an annual decline in Hl-no 
strandings, there were no month or spatial effects. A 
similar negative annual trend during 1992-2003 was 
not found in SC, an area that shares at least one bot- 
tlenose dolphin stock with NC (McFee and Hopkins- 
Murphy, 2002; McFee et al., 2006). Causes for the an- 
nual decline detected in this study are unknown. The 
lack of coastal segment or month effects was curious 
given the high seasonal variability in local abundance 
of coastal bottlenose dolphins along the NC coast, with 
more dolphins just south of Cape Hatteras in all sea- 
sons except summer (Torres et al., 2005; Waring et al., 
2010). Changes in abundance, habitat shifts, or survi- 
vorship rates could have resulted in these patterns, but 
data do not exist to test these hypotheses. 
Perinatal bottlenose dolphins were recovered in 
every month, although they were primarily bimodal 
with the spring mode more pronounced than the fall 
mode. This pattern is consistent with previous reports 
of neonate strandings in NC (Thayer et al., 2003) and 
SC (McFee et al., 2006). However, care should be tak- 
en when interpreting reproductive seasonality from 
stranded perinatal animals. On the basis of size alone, 
coastal bottlenose dolphins <125 cm could include 
calves up to 3 months of age (Fernandez and Hohn, 
1998). Unfortunately, a standardized data collection 
to assess whether a small dolphin was a true neonate 
( see Thayer et al., 2003) has not been consistent. As a 
result, the presence of perinatal strandings in Janu- 
ary, for example, does not necessarily mean that the 
dolphins were born in January. Also, it is possible that 
some of the smallest perinates were late-term aborted 
fetuses and their occurrence in the stranding record 
would influence interpretations of seasonality. Spatial 
patterns of perinatal strandings may result from differ- 
ences in local abundance along the coast during calving 
season; however, fine-scale abundance or density esti- 
mates are not available. 
Caveats on the use of stranding data as indicators of 
biodiversity and distribution 
Marine mammal strandings can serve as indicators of 
biodiversity and spatiotemporal presence of live ani- 
mals in nearby waters. Stranding data may also indi- 
cate changes in distribution, phenology, or mortality — 
some times before changes are detectable in source 
populations (Gulland, 2006). It is critical, therefore, to 
recognize the combination of stochastic and determinis- 
tic effects on the occurrence and discovery of stranded 
