268 
Fishery Bulletin 114(3) 
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I I Recruit (1 .5%) 
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Harvestable (84.7%) 
Shell height (mm) 
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Shell height (mm) 
Figure 4 
Frequency histograms of digitally sized shell heights (in 
millimeters) of sea scallops {Placopecten magellanicus) 
within (A) New York Bight (3213 sea scallops) and (B) 
Long Island areas (12,039 sea scallops). 
37.9% (4,563) were classified as larger than the size of 
recruits but smaller than the 4" rings. This distribu- 
tion yields an exploitable scallop density (of harvest- 
able size scallops) of 0.047 scallops per m^. The re- 
maining 0.9% (108) scallops were classified as recruits. 
The mean shell height for the region was 108 mm. As 
with the NYB sites, the scallop population was found 
to be dominated by scallops with a large shell height 
and only a small number of recruit-size scallops were 
observed (Fig. 5). 
Comparisons of results from dredge tows with those 
from camera imagery were performed for a subset 
of the surveys from the NYB region (NYB4-8). The 
dredged scallops were manually sized into 5-mm bins. 
The dredged scallop sizes were compared with shell- 
height sizes obtained with the AUV from the same 
surveys by using size-class distribution plots (Fig. 6). 
The means of the manually measured scallop shell 
heights obtained with dredging (range of mean values 
122-135 mm, N=54-22,) were found to be within 6% 
of the co-located AUV image-sized shell height means 
(range of mean values 117-130 mm, N=140-801, Fig. 
6). The lower means of the AUV image-sized scallops 
are expected because recruit-size scallops are included 
within the distribution. By design, dredges do not ac- 
curately sample scallops under 101.6 mm (4" diameter 
ring), thereby skewing the shell height distribution to- 
ward larger sizes (Yochum and DuPaul, 2008). 
Biomass 
Using a published equation (Eq. 2) we calculated the 
meat weight of each individual scallop from the shell 
height measurements derived from AUV images and 
the results are plotted in Figure 7. The majority of 
sea scallop biomass off LI is due to a high frequency 
of smaller meat weights (10-30 g each). The highest 
density sites in the LI region were typically coincident 
with smaller shell heights. The bulk of sea scallop bio- 
mass in the NYB region is due to a higher frequency of 
meat weights ranging from 30-50 g each. 
Fishing effort 
Digitized dredge scars in the side-scan mosaics re- 
vealed that over 174,000 m^ or 35.5% of the total 
surveyed seafloor area showed signs of dredging. We 
found that higher dredging effort (>7% of the bottom 
area dredged) coincided with the highest scallop den- 
sities, whereas a low scallop density area typically 
showed little or no dredging. It was not uncommon for 
a site to have a single dredge scar from a commercial 
vessel — perhaps the mark of a test dredge tow that 
did not yield a large enough catch for continued fish- 
ing effort. 
There was a noticeable difference between fishing 
efforts in LI and NYB. We found that the NYB had 
significantly less dredging (5% overall) than that 
found in the LI region. The scallop densities at all 
NYB sites were considerably less than those at LI 
counterparts. NYB8 had the most concentrated dredg- 
ing in the region with 11.9% of the area dredged. In 
addition, the shell height distributions for the heavily 
fished sites were positively skewed because of the size 
selectivity of the commercial scallop dredge (Fig. 5). 
The LI sites had an overall density 7 times that of 
the NYB region. As a result, the LI region had sig- 
nificant commercial dredging >18% of the total area 
dredged for 5 out of the 8 survey sites. Operationally, 
digitizing dredge scars did not add significant process- 
ing time of the data. After side-scan sonar mosaics 
had been produced for each site, it took a total of 8 
man-hours to manually digitize and calculate the area 
dredged for all 22 survey sites. 
