Recent Advances in Automated Genus-specific Marine Habitat Mapping Enabled by High-resolution Multibeam Bathymetry

There is a great need for accurate, comprehensive maps of seafloor habitat for use in fish stock assessments, marine protected area design, and other resource management pursuits. Recent advances in acoustic remote sensing technology have made it possible to obtain high-resolution (meter to sub-meter) digital elevation models (DEMs) of seafloor bathymetry that can rival or surpass those available for the terrestrial environment. The acquisition and processing of these data are expensive, however, requiring specialized equipment, expertise, and large amounts of both field and laboratory effort per unit area mapped. Further, the interpretation and classification of these data into maps of habitat type is typically (and appropriately) performed only by trained experts that are familiar with both seafloor geomorphology and the nature and limitations of the data sources. Because it is done visually, this interpretation can be very time-consuming and may yield subjective results that are not comparable from site-to-site or between individual interpreters. We applied an algorithmic terrain analysis approach to efficiently and objectively classify seafloor habitats using the quantifiable landscape metric Topographic Position Index (TPI). We used high-resolution multibeam bathymetry, together with precisely geolocated (± 5 m) ROV observations of fish distribution, to produce a preliminary genus-specific habitat suitability model for eight rockfish (Sebastes) species in the Del Monte shale beds of Monterey Bay, California. A high-resolution (2 m) multibeam bathymetry Digital Elevation Model (DEM) was generated and used to produce a derived TPI surface model using repeatable, algorithmic methods. This data layer, together with the positions and counts by species from 229 rockfish observations (2892 total fish) was then used to create preliminary predictive models of habitat suitability and fish distribution, as well as stock estimates for the study area. A second, independent fish observation data set was used to validate the models. and has put the entire rockfish fishery in peril of permanent collapse. With fewer fish of reproductive age living within the population, fish are unable to produce enough offspring to maintain sustainable levels, where sustainable levels are defined as being greater than 25% of the stock which would have existed without fishing pressure (PFMC, 2004). Creating effective management strategies to rebuild declining rockfish populations and maintain sustainable fisheries requires accurate estimates of current stock levels. In order to determine the effects of fishing pressure on fish growth and reproduction, the Magnuson-Stevens “Sustainable Fisheries” Act of 1996 mandated both state and federal management agencies to designate “Essential Fish Habitat,” areas where fish spawn, breed, mature and feed. In 1998, the Pacific Fisheries Management Council (PFMC) under direction from NMFS, identified the entire United States Exclusive Economic Zone (EEZ) of the west coast, which extends 200 miles out from the coastline, as Essential Fish Habitat. In an effort to produce more accurate, species-specific estimates of EFH, PFMC and NMFS prepared an environmental impact statement for Pacific Coast rockfish, which identified Habitat Areas of Particular Concern (HAPC) within areas designated as EFH (PFMC, 2004). In addition, a coast-wide GIS integrating data from various sources has helped to determine the location and extent of both HAPC and EFH along T I N T R O D U C T I O N here is a great need for accurate and efficient species-based identification and classification of marine habitats. Marine ecosystem health depends on the abundance and diversity of life within the ecosystem, as well as the quality of habitat associated with the area (Adams et al., 1995). Understanding the link between marine species and their habitats can help reveal ecosystem dynamics affecting both largeand small-scale patterns of species distribution and abundance. Over the past several decades, marine resources have been declining, and many species have reached critically low levels (Starr, 1998, 2002; Mason, 1999). The National Marine Fisheries Service (NMFS) manages 61 of the 96 species of rockfish (genus Sebastes) found along the Pacific Coast from Washington to California. Of these species, 9 are currently listed as “over fished. ” Other species often caught as “bycatch” during the harvest of economically important species have also declined in both number and overall length of individuals (PFMC, 2004). Rockfish are particularly vulnerable to over fishing. Many species are long-lived, have low fecundity, and slow growth and maturation rates (Yoklavich et al., 2000, 2002). Unlike most fish, rockfish tend to reproduce at greater rates with increased age (Love et al., 2002). For these reasons, increased fishing pressure has resulted in tremendous declines of many rockfish species,