A Better Understanding of Coral Reef Ecosystems

Pelagic predators such as these barracuda, Sphyraena qenie, are part of the coral reef ecosystem in the U.S. Line Islands (NOAA Photo by Kevin Lino).
A team of scientists have embarked from Hawai'i on a three-month survey of coral reef ecosystems at Johnston Atoll, the U.S. Phoenix Islands, the islands of American Samoa, and the U.S. Line Islands in the tropical Pacific Ocean. The overarching objective is to better understand the coral reef ecosystems of these areas, many of which are seldom explored. The research expedition is part of a regular monitoring program, conducted by the Coral Reef Ecosystem Division (CRED), headquartered in Honolulu, Hawai'i. The expedition is supported by NOAA's Coral Reef Conservation Program and involves extensive cooperation among NOAA scientists and research partners, including the University of Hawaii Joint Institute for Marine and Atmospheric Research (JIMAR), the U.S. Fish and Wildlife Service, San Diego State University, and the Papahānaumaokuākea Marine National Monument.

The research expedition will be carried out from February 27 to May 24, 2012 aboard the NOAA ship Hi'ialakai. Under the leadership of Chief Scientists Dr. Jill Zamzow, Dr. Bernardo Vargas-Angél, and Jamison Gove, a diverse team of researchers will be conducting multidisciplinary coral reef ecosystem surveys, assessing the status of fishes, corals, algae, marine invertebrates, and the oceanographic conditions in which these organisms exist. The scientific data collected during the three-month research expedition will enable informed and effective implementation of ecosystem-based management and conservation strategies for coral reef ecosystems, helping to ensure their protection for generations to come.

Saturday, April 16, 2011

Measuring Fish while Flying

by Jacob Asher and Danny Merritt

This year a pilot project has been implemented by CRED’s fish team using a stereo-video system on the fish-towboard to improve the team’s ability to precisely measure fish and benthic features, and to accurately define the size of the area surveyed. This project is being done in collaboration with the Harvey Lab at the University of Western Australia. Dr. Euan Harvey and his lab have been using stereo-video systems for both diver surveys and on baited camera systems [a method to attract fish or other animals into the field of view of a camera using bait] for a number of years, including the use of baited cameras (BRUVS) around Guam and the CNMI. The use of such a system on a towboard, however, is a novel technique.
Noah Pomeroy flying the stereo-video fish towboard at Pagan Island. NOAA photo by Jacob Asher.
Overall the implementation during this cruise, while it is still preliminary, has been successful despite a few challenges. During a towed-diver survey, the fish diver tries to ‘aim’ the towboard to ensure that fish pass by the field of view of both cameras. It has taken some time for the divers to become accustomed to the new cameras that are mounted on the towboards because they’re bulkier and harder to maneuver.  Also, the post-processing of the video files at the end of the day has been a challenge because of the volume of data that is collected. On a typical day of operations, the tow team collects approximately 6 hours of high-definition video on 2 cameras. The result? Huge videos that must be downloaded, converted to a usable format, and organized so that the videos can be analyzed later on.

Measuring Fish with Cameras
Stereo-photogrammetry (or stereo-video) is a technique CRED uses for sizing and ranging objects, such as fish, seen in video or still images. The method uses two images taken at the same time of an object from 2 different perspectives. If the relative orientation of both images is known, it is then possible to measure the distance from the camera to the point seen in the images. This is the same process by which people are able to judge distances with our two eyes. By knowing the location of 2 points on an object, such as the head and tail of a fish, the distance between the points (e.g. fish length) can also be calculated.

Above is an example of stereo-photogrammetry software being used to measure fish captured from BotCam video. In this case, two pink snapper have been measured.

CRED has been using stereo-video systems for baited camera systems for a number of years. An example from BotCam video (a deep baited camera system) of stereo-photogrammetry software is shown above.
Posted by NOAA CRED at 12:22 AM

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