Maria Madrigal: Understanding the Sampling Methods: April 4, 2012

NOAA Teacher at Sea

Maria Madrigal

NOAA Ship Oscar Elton Sette

April 2-18, 2012

Mission: Comparison of Fishery Independent Sampling Methods

Geographical area of cruise: Tutuila, American Samoa

Science & Technology Log: April 4, 2012

The goal of the study is to get a better picture of the coral reef fish assemblage using three different sampling methods. Two NOAA research vessels based in Honolulu, Hawaii (Oscar Elton Sette and Hi’ialakai) are working concurrently to assess coral reef fish assemblages around the island of Tutuila in American Samoa.

Three observational methods will be used to assess these reef fish assemblages; stationary point count divers (SPC), baited remote underwater video stations (BRUVS) and an autonomous underwater vehicle (AUV).

In the shallower areas being sampled (0 – 30 meters), all three survey methods will be used. In the areas ranging from 30-100 meters, only the BRUVS and AUV systems will be used as the divers can not reach these depths. This study will allow for a comparison among all three methods in the shallow-water depth range. The use of the BRUVS and AUV in the 30-100 m depths will also allow comparisons to be made between the shallow and deeper portions of the reef ecosystem to see if the patterns apparent in the shallow areas are similar to or different than those found in deeper waters.

SE12-02 Tutuila Comparison of Fishery Independent Sampling Methods for Coral Reef Fish
SE12-02 Tutuila Comparison of Fishery Independent Sampling Methods for Coral Reef Fish

The Hi’ialakai will be the base for the SPC (Stationary Point Count) divers.  Teams of two divers will work side-by-side sampling across a 30-meter transect. One diver is centered at the 7.5 meter mark and the other diver is centered at the 22.5 meter mark. Each diver samples a cylinder with a radius of 7.5 meters. Each diver spends the first five minutes noting the fish species present within their cylinder. After noting what fish species are present, the diver keeps a tally of how many representatives of each species are within their cylinder. Divers must work systematically to record additional data including total fish length and habitat type.  For a more detailed description of the SPC method, you may read the procedure as provided by PIFSC.

The Oscar Elton Sette will be the base for the BRUVS (Baited Remote Underwater Video Stations) and the AUV(Autonomous Underwater Vehicle) operations.

BRUVS are deployed from small boats at predetermined locations previously sampled by the SPC divers. They are placed on the seafloor and are equipped with two cameras that allow for accurate measurement of the fish that come into view. The BRUVS are deployed at each site for 20-minutes without bait and again for 60-minutes either with or without bait. The video can be instantly reviewed to ensure successful recording at each site. Captured video is reviewed and analyzed at a later date. Final video processing and data analysis will take place once the scientists return to the lab.

The AUV, named Lucille, is designed to hover 2-4 meters above the seafloor. It is programmed to navigate a predetermined survey track before it is deployed. It is equipped with a pair of forward-looking stereo-video cameras, two still-image cameras, a CTD (Conductivity-Temperature-Depth) sensor and a SONAR (Sound Navigation and Ranging) unit. It can dive down to 1,500 meters and can go on missions that last up to eight hours. It is programmed to come back to the ocean’s surface at the end of its mission.  The video and still photographs are later reviewed and analyzed. All the data collected by the AUV allows scientists to get a better picture of the ocean floor, what lives there and how many organisms are living within that community.

Comparison of Survey Methods
Comparison of Survey Methods

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