Kneebone et al.: Seasonal distribution and habitat use of the A/opias vulpinus in the western North Atlantic Ocean 403 
Adult male: 2188 cm 
YOY: $100 cm || Juvenile male: 101-187 cm | 
500 { | 
Adult female: 2216 cm 
Number of sharks 
150 
Sex 
Pa Unknown 
[ Male 
[| Female 
200 300 
Fork length (cm) 
Figure 2 
Length-frequency histogram for 3072 common thresher sharks (Alopias vulpinus), representing 
males, females, and those with unknown sex for which a measured or estimated length was avail- 
able, captured from 1964 through 2019 in the western North Atlantic Ocean. The classification of 
life stages, based on sizes at 50% maturity from Natanson and Gervelis (2013), is provided at the 
top of the figure for males and females. YOY=young of the year. 
stages almost exclusively represent sharks captured in 
US. waters. 
Gear interactions 
Common thresher sharks were captured with a wide 
range of gear types, including commercial bottom long- 
line, pelagic longline, gill net (sink and floating), haul 
(beach) seine, purse seine, (bottom) otter trawl, mid-water 
trawl, and recreational rod and reel (Fig. 1). Of these 
gears, gill nets (50.0%; primarily sink gill nets) and 
pelagic longlines (27.1%) accounted for the majority of 
capture records, followed by rod and reel (10.4%) and otter 
trawl (9.2%). All other gears accounted for no more than 
1.4% of the total number of records. The most common life 
stage of sharks captured by gill nets was YOY (88.4%), but 
YOY sharks were also caught by otter trawls, haul seines, 
and rod and reel (Fig. 3). Juveniles were captured by all 
gear types but were most commonly taken in gill nets 
(43.1%) and pelagic longlines (33.3%). Adults were cap- 
tured by every gear type except haul seine, but they most 
commonly were taken by pelagic longline (39.2%) and rod 
and reel (26.7%). 
Seasonal distribution 
Common thresher sharks were captured over a broad 
geographic range extending from 23.9°N to 46.3°N and 
from 42.8°W to 95.1°W (Fig. 4). The majority of records 
(number of sharks [n]=2751; 79.1%) were from conti- 
nental shelf waters shallower than 200 m; however, 
numerous individuals (n=727; 20.9%) were encoun- 
tered in deeper (>200 m) offshore waters of the WNA. 
Records were available from all months and seasons 
with the greatest number of them from the winter 
(Table 2). The increase in capture records during win- 
ter was partially due to a large number of YOY and 
juveniles being taken in 2018 by gill-net fisheries off 
North Carolina. 
Throughout the year, north-south changes in distribu- 
tion along the east coasts of the United States and Can- 
ada were noted for common thresher sharks over all life 
stages. In general, individuals occurred at more northerly 
latitudes in the summer and more southerly latitudes in 
the winter (Fig. 4). During the winter, sharks were primar- 
ily encountered off the coast of North Carolina, both in the 
vicinity of Cape Hatteras and in waters near the edge of 
the continental shelf. A considerable number of specimens 
were also caught in continental shelf waters off the east 
coast of Florida during the winter. Sharks were distrib- 
uted over the broadest area during the spring, with the 
center of distribution from North Carolina to Long Island, 
New York. During the summer, sharks were captured most 
commonly in continental shelf waters off the mid-Atlantic 
states, southern New England, and the Gulf of Maine, and 
sharks were rarely encountered south of Maryland. In the 
