Smooth Bottom Net Trawl Fishing Gear Effect on - New England ...

NOAA/NMFS Unallied Science Project, Cooperative Agreement NA16FL2264 December 2005
<strong>Smooth</strong> <strong>Bottom</strong> <strong>Net</strong> <strong>Trawl</strong> <strong>Fishing</strong> <strong>Gear</strong> <strong>Effect</strong> on the Seabed:
Investigation of Temporal and Cumulative <strong>Effect</strong>s BKAM/CR
3.3 Video Sled Results
Visual observations and side-scan data (Section 3.2.2) indicate that the seafloors at Mud Hole
and Little Tow represent quite different habitats. These observations were originally made in
2001 and were again confirmed during the 2002 study. The seafloor at Mud Hole consists of
fine-grained sediments that form hard, flat mud in the northern region (Plates 3.3-1 and 3.3-2)
and gradually grade into hummocky flocculent mud in the southern region (Plates 3.3-3, 3.3-4,
3.3-5, and 3.3-6). Much of the surface of the seafloor in Mud Hole appears to be structured by
biological forces, as evidence are numerous microtopographic features such as tubes, feeding
depressions, mounds, and tracks and trails. In contrast, much of the seafloor at Little Tow
appears to be structured by physical forces. At Little Tow the seafloor is muddy only in the
northern region (Plates 3.3-7 and 3.3-8) and grades into rippled sand and well-defined sand
waves in the southern region (Plates 3.3-9, 3.3-10, 3.3-11 and 3.3-12). The sandier regions
evidence much less infaunally produced microtopography, such as tubes, feeding depressions
and mounds. Additionally, shell material tends to be more abundant in Little Tow. Within-region
habitat variability (patchiness) also appears to be much more pronounced in Little Tow.
Several interesting phenomena were observed in the video. Side-scan data had indicated largescale
changes in the sea floor of Little Tow following a strong northeastern storm in middle
November. Basically, the sea floor in the entire southern region of Little Tow was changed into
large expanses of very uniform sand ripples. These ripples were very visible on the video (Plate
3.3-13). Additionally, while trawl marks were very evident on the video footage collected in
2001, this was not the case in 2002. Very few instances of seafloor disturbance by fishing gear
was noted in 2002. This may well have been an artifact of the exceptionally poor visibility that
was encountered in 2002. In 2001, trawl marks were the most evident in the ROV footage which
approached the lanes perpendicular to the direction of tow. While the 2002 video-sled drifts also
approached the lanes perpendicular to the direction of tow, the camera needed to be kept right on
the bottom, which substantially hampered the depth of field and shadowing necessary to discern
seafloor structure.
3.3.1 General Faunal Patterns
Seven identifiable species categories of fish were observed on the video-sled footage. Some
representative species are shown on Plate 3.3-14. A total of 432 fish were seen, 278 in Mud Hole
and 154 in Little Tow (Table 3.3-1- raw video sled counts). The most abundant of these were red
hake (185 individuals), flounder (121 individuals), silver hake (33 individuals), sculpin (32
individuals), and ocean pout (24 individuals). Additionally, two skates, one sea robin, and 34
unidentified fish were also seen. Some differences in the composition of the fish fauna were
noted between the two study areas. Red hake totally dominated the fish in Mud Hole, accounting
for 50% of the fish seen, but only accounted for 29.8% of the fish seen in Little Tow. Flounder
were present in roughly equal proportions, accounting for 27.7% and 28.5% of the fish seen at
Mud Hole and Little Tow, respectively. Sculpin and silver hake accounted for a greater portion
of the fish seen in Little Tow (14.9% and 10.4%, respectively) than in Mud Hole (3.3% and
6.1%, respectively).
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