74 
Fishery Bulletin 106(1 ) 
ter mixed MU decreased to 19 animals per year; both 
estimates were below their corresponding PBR level. 
Reductions in bycatch estimates were attributed to a 
reduction in fishing effort, as measured in landings. 
In particular, fishing effort was drastically reduced for 
spiny dogfish, which was listed as overfished by the 
National Marine Fisheries Service (NMFS) in 1998 
(Federal Register, 1998). Fishery Management Plans 
(FMPs) were implemented by NMFS for federal waters 
(Federal Register, 2000a, 2000b), and by state agencies 
for state waters (ASMFC 2 ), to reduce fishing effort. 
The purpose of this study was to conduct a post-hoc 
analysis of bottlenose dolphin strandings in NC in re- 
lation to fisheries bycatch estimates and spiny dogfish 
landings. First, the frequency of stranded dolphins ex- 
hibiting signs of fishery entanglement was examined 
to determine if this frequency reflected corresponding 
levels of estimated dolphin bycatch. Second, it was hy- 
pothesized that the frequency of those strandings would 
decrease concomitant with a reduction in spiny dogfish 
landings, but that the frequency of stranded dolphins 
without signs of entanglement would not change. Lastly, 
two methods for establishing stranding threshold lev- 
els were evaluated to determine if they could be used 
in real-time to detect increases in fisheries bycatch 
before revised bycatch estimates are available or when 
observer programs do not exist. 
Materials and methods 
Fishing-effort data 
Monthly landings data on spiny dogfish caught in com- 
mercial ocean gill nets off NC from November 1997 
through April 2005 were obtained through the Trip 
Ticket Program of the North Carolina Division of Marine 
Fisheries (NCDMF). These data were used to determine 
the timing and magnitude of effort reduction in the 
spiny dogfish fishery for comparison with the frequency 
of bottlenose dolphin strandings. 
Stranding data 
Data were derived from ocean-side bottlenose dolphin 
strandings in NC between November 1997 and April 
2005 (n = 580) and were stratified by season: winter 
(November-April) and summer (May-October). These 
seasons reflect both the seasonal definition for bottlenose 
dolphin MUs and the two commercial fishing seasons for 
spiny dogfish as defined by the FMP November 1997 was 
chosen as the beginning of the winter season because 
this month marked the beginning of the first spiny 
2 ASMFC (Atlantic States Marine Fisheries Commis- 
sion). 2006. Review of the Atlantic States Marine Fish- 
eries Commission’s interstate fishery management plan for 
spiny dogfish ( Squalus acanthias) May 2004-April 2005 
fishing year, 18 p. Prepared by the Spiny Dogfish Plan 
Review Team, ASMFC, 1444 Eye Street, NW, 6th Floor, 
Washington, DC 20005. 
dogfish season in NC (November-April) for which there 
was consistent coast-wide coverage of the NC shore for 
strandings. April 2005 was the end of the last season for 
which landings data were available for this study. 
All reported stranded bottlenose dolphins were eval- 
uated for signs of human interaction (HI) and then 
classified as Hl-yes (i.e., with signs of HI), Hl-no (i.e., 
no signs of HI), or HI-CBD (could not be determined) 
(Kuiken et al., 1994; Read and Murray, 2000). Stranded 
dolphins categorized as Hl-yes were further stratified 
as fishery interaction (HI-FI) (e.g., entanglement lesions 
or gear present) or Hi-other (e.g., mutilation, propeller 
wounds evident). All stranded dolphins classified as 
Hi-other in our data set (n=12) were mutilated but too 
decomposed to determine if entanglement lesions were 
also present; therefore, they were treated separately. 
Animals were categorized as HI-CBD when it could 
not be determined whether or not the animal exhibited 
signs of HI because of factors such as decomposition, 
significant damage by scavengers, or lack of experience 
on the part of the stranding responder. 
Several criteria were established for the stranding re- 
cords used in this study. Animals genetically confirmed 
as being the offshore morphotype (?i = 6) were excluded 
so that comparisons could be made to bycatch data of 
coastal bottlenose dolphins. Animals <119 cm in total 
length (>i = 109), presumed to be neonates (Fernandez 
and Hohn, 1998), were also excluded to prevent a bias 
from the high natural mortality rates of neonates dur- 
ing the spring and fall birthing seasons (Hohn, 1980; 
Thayer et al., 2003). Unless they were classified as 
adults, stranded dolphins for which no total length 
was recorded were excluded (n= 21). Dolphins removed 
from gear other than a gill net (e.g., trawlers, crab pots, 
hook-and-line gear) were also excluded (n- 5). 
Stranding rates through time were examined in rela- 
tion to bycatch estimates and changes in fishing effort 
in the spiny dogfish fishery. Regression analyses (SAS, 
vers. 9.1, SAS Inst., Inc., Cary, NC) were used to com- 
pare the number of HI-FI strandings per season (winter 
and summer) per year to the corresponding bycatch 
estimates for ocean gill nets provided in Rossman and 
Palka. 1 Because stranding rates can never be less than 
zero, the regression line was forced through the origin. 
Rank-sum tests for each HI category were used to deter- 
mine if the mean number of bottlenose dolphin strand- 
ings per month was different between the first time pe- 
riod (TP1: November 1997-October 2000), when bycatch 
estimates were greater than the PBR levels, and the 
second time period (TP2: November 2000-April 2005), 
when bycatch estimates were either less than PBR levels 
or were unknown. For the rank-sum tests, only winter 
data (November-April) were used after a preliminary 
investigation of spiny dogfish landings revealed that 
the fishery operates only off NC during those months. 
Stranding thresholds 
Two methods were used to calculate stranding thresh- 
olds. One calculation emulated a method currently 
