Cowen et al Evaluation of the In Situ Ichthyoplankton Imaging System and comparison with the bongo-net sampler 
5 
Figure 3 
Example of a full-frame image collected with the In Situ Ichthyoplankton Imaging System (ISIIS). Larval fish (small [~4 mm], 
Paralichthys dentatus ) and other plankters (especially copepods) are evident throughout. The small circular and elongate 
particles are diatoms (centric and pinnate) and diatom chains, which can be detected but are too small to clearly resolve. Also 
seen is a ~1.5-cm ctenophore with tentacles retracted. Several small aggregates (marine snow) are evident in the full-frame 
image. Overall, the full frame provides a good indication of the plankton field encountered by the observed larval fish. Sur- 
face is to the top of the image. Select plankters are shown to the right of the full frame in higher magnification (from top to 
bottom): (A) chaetognath (note that an improved image has been substituted for demonstration purpose only), (B) preflexion 
stage larval fish, (C) marine snow, (D) small copepod, (E) 2 copepods, (F) diatom chain (rotated to fit figure), and (G) copepod. 
about 15% of the imaging field (i.e., the image field of 
view was 11 cm versus 13 cm). In comparison, the typi- 
cal bongo sampled 137 m 3 per oblique tow, for a total 
volume sampled of 1506 m 3 . The maximum depth of 
tows was 49 m for ISIIS tows and 52 m for the bongo 
tows. 
The water column along both transects was defined 
by limited vertical stratification, especially in its upper 
35 m (Fig. 2). A slight decrease in chlorophyll concen- 
tration below a depth of -35 m in the inshore portion 
of the easterly transect was apparent and also was 
observed with a change in temperature and salinity; 
still, the differences were small. In contrast, consider- 
able horizontal variation (south to north) was observed 
in hydrography along both transects with tempera- 
ture lower, salinity lower, and chlorophyll fluorescence 
higher in the inshore (northern) portions than in the 
offshore (southern) portions (Fig. 2). 
The productivity of the water column was evident 
in ISIIS imagery as a preponderance of diatoms vis- 
ible throughout most images (Fig 3). Also imaged were 
a variety of invertebrate plankters, ranging from co- 
pepods and larvaceans to ctenophores and medusae 
to invertebrate larval types, such as echinoderm plu- 
teus. Because most imagery was dominated by the 
smaller plankton (diatoms, copepods, and larvaceans; 
