Mapping Fish Habitat Off St. Croix: A Spring Break Aboard NOAA Ship Nancy Foster

From March 15 to April 3, 2014, the NOAA Ship Nancy Foster worked off St. Croix in the U.S. Virgin Islands. The expedition's main goal was to map central fish habitat on the seafloor offshore. Among those aboard was a geography student from Middlebury College in Vermont, spending his spring break as a NOAA intern, who wrote about the work for NOAA's coastal science blog. Life at sea, he found, was more comfortable than expected, with an exercise room, a spacious TV room and very good food.

Mowing the lawn with sonar

The ship's multibeam sonar builds a continuous picture of the ocean floor. The ship runs back and forth along parallel lines, collecting data on the depth and character of the bottom and on the size and number of fish.

Sonar coverage around St. Croix so far: colder colours are deeper, warmer colours shallower. Image from NOAA.

Sometimes the lines end up slightly too far apart and leave gaps in the data, which surveyors call "holidays". Late in the trip the team went back over those areas to fill them in.

Holidays in the data on the shallow eastern side of St. Croix. Image from NOAA.

Cleaning the data

The intern's main job was processing the sonar data. Some of it comes out clean; some needs trimming of stray, noisy points before it is usable.

Clean sonar data… Image from NOAA.

… and data that needs a trim. Image from NOAA.

Once processed, the backscatter, the strength of the sound returned from the bottom, helps characterize the seafloor and pick out places that may be fish habitat. The team then sends a remotely operated vehicle (ROV) down to see what is really there, and its video comes back to the ship live.

An eagle ray seen by the ROV. Image from NOAA.

Why it matters

Put together, the sonar maps, backscatter and ROV video show which species and habitats are found around the island and where. They are a starting point for future research, and they help St. Croix's natural resource managers protect and conserve its marine life.

Sunset over St. Croix. Image from NOAA.

Sources

• NOAA National Centers for Coastal Ocean Science, "2014 Nancy Foster Mission: How I Spent My Spring Break," written by a student intern aboard; rewritten in hubnx's own words. Images from NOAA.