Assessing Bottom Gear Impact in the WGOM Closure Area: A Multifaceted Approach

Mashkoor Malik presented the results of a UNH Center for Coastal and Ocean Mapping (CCOM) study of the seafloor of the WGOMCA. Objectives The objectives for the CCOM study were to: • Construct a bathymetric map of Jeffrey’s Ledge to serve as a framework for subsequent studies. • Test the potential use of multibeam sonar to monitor fishing gear impacts. • Determine if it is possible to observe closure impacts with multibeam sonar

Investigation of bottom fishing impacts on benthic structure using multibeam sonar, sidescan and video

Bottom fishing gear is known to alter benthic structure, however changes in the shape of the sea floor are often too subtle to be detected by acoustic remote sensing. Nonetheless, long linear features were observed during a recent high-resolution multibeam sonar survey of Jeffreys Ledge, a prominent fishing ground in Gulf of Maine, located about 50 km from Portsmouth, NH. These marks, which have a relief of only few centimeters, are presumed to be caused by bottom dredging gear used in the area for scallop and clam fisheries. The extraction of these small features from a noisy data set (including several instrumental artifacts) presented a number of challenges. To enhance the detection and identification of these features, data artifacts were identified and removed selectively using frequency filtering. Verification was attempted with sidescan sonar and video surveys. While clearly visible on the sidescan sonar records, the bottom marks were not discernable in the video survey. The inability to see the bottom marks with video may be related to the age of the marks, and has important ramifications about appropriate methodologies for quantifying gear impact. Results from multibeam sonar, sidescan sonar and video surveys suggest that the best methodology to deal with inspection of bottom fishing marks is to integrate data in a 3D GIS-like environment

Advanced Mid-Water Tools for 4D Marine Data Fusion and Visualization

Mapping and charting of the seafloor underwent a revolution approximately 20 years ago with the introduction of multibeam sonars -- sonars that provided complete, high-resolution coverage of the seafloor rather than sparse measurements. The initial focus of these sonar systems was the charting of depths in support of safety of navigation and offshore exploration; more recently innovations in processing software have led to approaches to characterize seafloor type and for mapping seafloor habitat in support of fisheries research. In recent years, a new generation of multibeam sonars has been developed that, for the first time, have the ability to map the water column along with the seafloor. This ability will potentially allow multibeam sonars to address a number of critical ocean problems including the direct mapping of fish and marine mammals, the location of mid-water targets and, if water column properties are appropriate, a wide range of physical oceanographic processes. This potential relies on suitable software to make use of all of the new available data. Currently, the users of these sonars have a limited view of the mid-water data in real-time and limited capacity to store it, replay it, or run further analysis. The data also needs to be integrated with other sensor assets such as bathymetry, backscatter, sub-bottom, seafloor characterizations and other assets so that a “complete” picture of the marine environment under analysis can be realized. Software tools developed for this type of data integration should support a wide range of sonars with a unified format for the wide variety of mid-water sonar types. This paper describes the evolution and result of an effort to create a software tool that meets these needs, and details case studies using the new tools in the areas of fisheries research, static target search, wreck surveys and physical oceanographic processes

Effects of a Large Fishing Closure on Benthic Communitites in the Western Gulf of Maine: Recovery from the Effects of Gillnets and Otter Trawls

The recovery of benthic communities inside the western Gulf of Maine fishing closure area was evaluated by comparing invertebrate assemblages at sites inside and outside of the closure four to six years after the closure was established. The major restriction imposed by the closure was a year-round prohibition of bottom gillnets and otter trawls. A total of 163 seafloor sites (~half inside and half outside the closure) within a 515-km2 study area were sampled with some combination of Shipek grab, Wildco box corer, or underwater video. Bottom types ranged from mud (silt and clay) to boulders, and the effects of the closure on univariate measures (total density, biomass, taxonomic richness) of benthos varied widely among sediment types. For sites with predominantly mud sediments, there were mixed effects on inside and outside infauna and no effect on epifauna. For sites with mainly sand sediments, there were higher density, biomass, and taxonomic richness for infauna inside the closure, but no significant effects on epifauna. For sites dominated by gravel (which included boulders in some areas), there were no effects on infauna but strong effects on epifaunal density and taxonomic richness. For fishing gear, the data indicated that infauna recovered in sand from the impacts of otter trawls operated inside the closure but that they did not recover in mud, and that epifauna recovered on gravel bottoms from the impact of gillnets used inside the closure. The magnitudes of impact and recovery, however, cannot be inferred directly from our data because of a confounding factor of different fishing intensities outside the closure for a direct comparison of preclosure and postclosure data. The overall negative impact of trawls is likely underestimated by our data, whereas the negative impact of gillnets is likely overestimated