Scanning the Ocean Floor for Fish Habitat

by Eric Weather

Maximizing the Efficiency of Reef Fish Surveys Through IncorporaThe Gulf of Mexico benthic habitat can be summarized as a mosaic of sand with limestone rock outcroppings (reefs).  These reefs facilitate the settlement and growth of a wide variety of benthic organisms including corals, sponges and crustaceans.  They also support a diverse fish community from tiny blennies and gobies to commercially and recreationally important groupers and snappers.  The Fisheries-Independent Monitoring (FIM) program in cooperation with the National Marine Fisheries Service (NMFS) conducts annual fisheries monitoring on these reef habitats to provide data for single species and ecosystem-based management initiatives.  In 2009, the FIM program implemented the use of side-scan sonar to identify and classify the benthic habitats in the eastern Gulf of Mexico between 10 m and 110 m deep.  These sonars are towed behind a survey vessel and are equipped with two side-facing transducers that generate and receive sound signals.  When a signal is generated it propagates through the water column and reflects off the seafloor and then back to the transducer.  The intensity at which the return signal is received is interpreted into an image that is deciphered by a trained survey technician.  The configuration of the transducers on the sonar allows the sound signal to ensonify a very wide swath of the seafloor (up to 300 m) at one time.  As the survey vessel moves through the water, a streaming image of the seafloor is generated, as depicted in the video.  When rocky outcrops are identified by a survey technician they are given a habitat category based on their structure and complexity and become the basis for the NMFS/FIM reef-fish survey.  Additionally, these data are used by regional geologists, cartographers and other biologists to help answer a wide variety of research related questions regarding the benthic habitats of the eastern Gulf of Mexico.