Project Summary for 2005–07B: Grouper demographics and habitat engineering in the shelf-edge MPAs in the Gulf of Mexico
Objective 1: To visually compare 4 to 5 fished grouper (gag and scamp) spawning aggregations with 4 to 5 unfished spawning aggregations in the northeastern Gulf of Mexico.
Methods: The NURC ROV was used to make multiple transects through grouper aggregation sites within and outside of the 5–year old Madison Swanson experimental fishery reserve. Video and still records of ROV transects are then used to measure fish abundance, size, and diversity, and habitat characteristics of each aggregation site.
Significance: Fishery Management Councils are interested in using MPAs as management tools but first require qualitative information on their efficiency. Heavy fishing pressure on certain grouper species causes demographic distortion (truncation of size and age, and a loss of males) which, in turn, causes a reproductive bottleneck. This work will help answer the question: Do MPAs protect grouper demographics and spawning?
Objective 2: To investigate the age, physical appearance, and geological characteristics of different geologic features in the reserves, including:
Methods: Rocks to be sampled were located with the ROV. The ROV remained in video contact with the selected rocks. Trimix divers descended down the ROV umbilical and used hammers and chisels to break off chunks of rock, then sent the rocks to the surface in labeled lift bags. The collected rocks and videos of their formations are presently being analyzed by Scanlon and her colleagues at the Woods Hole USGS laboratory.
Significance: Geology is the foundation of offshore reef habitat, and reef fish are tightly associated with such habitat. It is important to understand the nature and origin of rocky reefs and reef fish associations with various types of rocky formations.
Objective 3: To investigate the mechanism of shelf–edge pit formation. (The preferred hypothesis is that pits are excavated by red grouper. Alternate hypotheses include formation by gas escape or by freshwater seeps.)
Methods: Shelf–edge pits to be sampled were located with the ROV. The ROV remained in video contact with the pits. Trimix divers descended down the ROV umbilical and collected rocks, sediment, and water samples from the pits that would be used to evaluate the origin of the pits. Rocks, sediment, and water samples are presently being analyzed by Scanlon and her colleagues at the Woods Hole USGS laboratory.
Significance: The origin of large marine benthic pits have not been confirmed by direct observation. It is often assumed that they are produced by either natural gas emission or by freshwater seeps. Prior NURC observations of shelf–edge pits (June 2004) together with shallow–water experimental studies strongly suggest that these pits are red grouper excavations. Because these pits provide important habitat to many offshore species, it is important to understand their origin.
Objective 4: To compare the geologic and biologic characteristics of presumed red grouper excavations recently discovered in Madison–Swanson and adjacent sites with those already described for Steamboat Lumps.
Methods: The NURC ROV was used to obtain a video record of the fishes and invertebrates associated with many presumed red grouper excavations. Video tapes are being analyzed at the Coleman–Koenig laboratory at FSU.
Significance: Because these excavations provide habitat for many species, including the young of economically important red snapper and vermilion snapper, it is important to understand their origin and function.
Objective 5: To investigate activities associated with sound production on gag and red grouper spawning sites during the spawning season.
Methods: An in situ recording device (LARS) designed and constructed by Dr. David Mann at the University of South Florida was deployed at a grouper aggregation site for the purpose of recording grouper sounds produced around the time of spawning. The act of spawning was assumed from rapid ascents of groupers. Rapid ascents were recorded on in situ VR2 receivers. The VR2s recorded depth-indicating transmitters previously implanted in several groupers. The VR2s and the LARS system were synchronized before deployment. Thus, the VR2 monitored vertical fish movement and the LARS monitored fish sounds. The data from this study is being analyzed in David Mann’s Laboratory at the University of South Florida.
Significance: Many species of groupers produce sounds which are associated with various behaviors. If they make specific sounds associated with spawning, then other spawning aggregations could be located by towing an array of receivers. Also, it would be possible to estimate the impact of fishing on spawning by monitoring the spawning frequency of fished relative to unfished spawning aggregations.
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