Tuesday: June 4, 2013
Log Day 3
Dr. Laura Kracker
Geographer
NOAA / NOS / NCCOS
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Maps of fish density give a broad picture of how fish are distributed around reef structure. The size of the yellow dots represents the number of fish at each location along the transect.
Click here for larger view.
(Photo: Laura Kracker) |
Day 3 is always a very good day on a research mission. The scientists
and crew are getting settled in on the NOAA ship Nancy Foster. A familiar routine begins to take
shape. Yesterday I focused on making sure that all the computers were set up properly and my
logs were ready to begin fisheries acoustic surveys.
Fisheries acoustic surveys? - you might ask. On this mission, acoustic surveys refer to mapping fish in the water column - think sonars or fancy fish finders. From the hull of the NOAA ship Nancy Foster, sonars send a sound wave or 'ping' toward the seafloor as the ship travels along a transect line. The ping is reflected off fish or other critters swimming by. The sonars 'listen' for the echo of the ping bouncing back toward the ship - just like hearing your voice echo back when you holler across a canyon. The time it takes for the echo to return tells us how deep or far away the fish are. Larger fish have a stronger echo return. By using these two pieces of information (echo travel time and echo strength), along with the ship's GPS, we can map all the echo returns to determine where the fish are and their size.
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Echogram.
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(Photo: Laura Kracker) |
Echograms allow us to monitor data that is being collected along the acoustic survey transect. The red line is the echo return from the seafloor. The blue and green areas are fish schools (upper Echogram image). Individual echoes from fish and other organisms can be seen in the Echogram image below.
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Echogram
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(Photo: Laura Kracker) |
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Laura Kracker monitors fisheries acoustic sonar aboard the NOAA Ship
Nancy Foster.
(Photo: Debbie Meeks) |
For many years, divers have studied and explored the ledges and reefs of the Sanctuary where fish
gather to feed and find protection from predators. On this mission they will continue to do that. By making maps using acoustic surveys from the ship, we can travel over larger regions quickly and map fish across the unique seafloor habitats at Gray's Reef.
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