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Fishery Bulletin 1 1 1 (1) 
data for fisheries management. All these efforts are 
limited by the 3 factors described above: rarity, patchi- 
ness, and cost. The In Situ Ichthyoplankton Imaging 
System (ISIIS; Cowen and Guigand, 2008) has the po- 
tential to minimize all 3 limitations, and, if successful, 
would provide the stock assessment toolbox with robust 
and timely fishery-independent measures of spawning 
distribution and stock size based on early-life-stage in- 
formation. The overall goal of this study, therefore, was 
to evaluate the effectiveness of ISIIS for quantifying 
fish larvae and thus show the potential benefits of its 
integration into larval surveys, with the ultimate goal 
of improving stock assessments. 
Specifically, we compare ISIIS with a traditional 
bongo sampler, which is composed of a frame support- 
ing paired nets with mouth openings on either side of 
and in front of the towing wire (Posgay and Marak, 
1980). The bongo has been used in ichthyoplankton 
programs throughout the United States since its de- 
velopment in the late 1960s: in the shelf ecosystem of 
the northeastern United States since 1971 (Richardson 
et al., 2010), in the Gulf of Mexico since 1982 (Lycz- 
kowski-Shultz and Hanisko, 2007), and in the north- 
east Pacific Ocean since 1972 (Matarese et al., 2003). 
Here we present a comparison of larval fish abundance 
and size distribution based on results from the ISIIS 
and bongo sampler. 
Methods 
This study was conducted 54 km south of Woods Hole, 
Massachusetts, (Fig. 1), on 23-24 October, 2008, on 
the NOAA Ship Delaware II. The cruise immediately 
followed the passage of a low-pressure system, which 
brought strong winds to the study area; these winds 
diminished throughout the duration of the cruise. Sam- 
pling was completed along 2 parallel transects, which 
were 41.4 and 27.7 km in length and separated by -6 
km. To complete the comparison, the prototype ISIIS- 1 
(herein referred to as ISIIS) was towed along a tran- 
sect; then the ship returned to the beginning of the 
transect, and net samples were made with the bongo 
over the same transect. Sampling along each transect 
encompassed both day and night periods, but no at- 
tempt was made to compare day and night differences 
in larval abundance or vertical distribution. Morse 
(1989) compared daymight catches in the region and 
found no significant differences for most of the taxa 
captured in this study. He did find some daymight bias 
at larger transect lengths, but, in our study, both the 
bongo net and ISIIS sampled during day and night, 
and therefore we assume this length bias was random- 
ly distributed between the gears. 
Sampling gear 
The imaging output from ISIIS is unique in that it pro- 
vides a continual image for the entire tow duration, 
with a pixel resolution of -68 pm. Such fine resolu- 
tion enables detection of particles as small as a 100 pm 
(e.g., diatoms), although the ability to clearly resolve 
particles is typically in the range of 700 pm (i.e., small 
copepods and larvaceans) and larger sizes (e.g., larval 
fishes, chaetognaths, and ctenophores). One distinctive 
feature of ISIIS is its large depth of field (—30 cm for 
Figure 1 
Eight-day average (20-27 October 2008) sea-surface temperature (SST, °C) of northeastern U.S. continental shelf from 
Cape Hatteras, North Carolina, to Nova Scotia, Canada. (A) The sampling location offshore of Martha’s Vineyard, 
Massachusetts. (B) The inset shows the 2 In Situ Ichthyoplankton Imaging System (ISIIS) transects and the bongo 
collection locations marked by black dots along the same transects. Note the change in SST scale between the 2 panels. 
