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Puerto Rico Cruise Day 5
operate the SCUBA seine
Photo: Abby Poray
Today the fish survey teams focused on collecting specimens from vegetated areas, mainly seagrass, near reefs and mangroves to examine differences in habitat use. Our gear of choice - the SCUBA seine. The SCUBA seine is a modified beam trawl net that is pushed along the substrate by divers. The mouth of the net is held open by a rectangular PVC frame. The net tapers off in the back to what is termed the cod end. From casual observation of our hauls today, it appears that more fish were caught in seagrass near mangroves versus seagrass adjacent to low-relief reef areas.
Photo: Abby Poray
Photo by Abby Poray
Our catch was typically dominated by parrotfish. You might be wondering how we choose our samples sites and how we are able to accurately navigate to the sites day after day. We use a piece of equipment called the GPS Pathfinder® System. GPS stands for Global Positioning System which is a satellite-based positioning system operated by the US Department of Defense. Over 24 operational NAVSTAR satellites orbit Earth every 12 hours, providing worldwide, all-weather, 24-hour time and position information.
Photo: Amy V. Uhrin
The Pathfinder System consists of an interconnected beacon antenna, receiver, and logger. The antenna is held upright and collects satellite broadcasts, filtering out any unwanted signals and amplifying the necessary ones. The broadcasts are transmitted from the antenna to the receiver which decodes the broadcasts and uses specialized corrections to provide sub-meter position accuracy. The corrected positional information is then sent to the logger. Using this system, we are able to collect extremely accurate single point locations (latitude and longitude) from where the antenna was held. So, once we find an area that meets our criteria for sampling, we erect the beacon antenna and collect a coordinate. The coordinates are saved in the logger and can be recalled at a later date when we wish to return to the same site. To do this, we erect the beacon, and open the coordinate file in the logger. The system again uses the satellite broadcasts to determine where the beacon is currently erected in reference to the saved coordinate. The system then indicates how far away from the point we are and in which direction we need to head in order to reach the point. The system continually updates the information as you move closer and closer to the target.
Tracy Hamburger and Scientist Abby Poray
navigate to a site
using the Pathfinder System
Photo: Amy V. Uhrin