Using remote sensing, in situ observations, and geographic information systems to map benthic habitats at Heceta Bank, Oregon

Graduation date: 2003Dramatic declines in many species of demersal fishes off the West Coast have\ud resulted in the designation of nine commercially important species as being\ud overfished. While the causes of those declines are not clearly understood, the\ud fact remains that a paucity of life history and abundance data exists for many\ud demersal species, also known as groundfish. Due to this uncertainty, only 21\ud of the 82 species of groundfish managed under the Groundfish Fishery\ud Management Plan of the Pacific Fishery Management Council (PFMC) have\ud been fully assessed. One challenge in designing a systematic survey of\ud groundfish resources is that many species associate with heterogeneous\ud substrate of varying relief. In many areas, the rugosity of the substrata\ud precludes sampling by conventional techniques (e.g. bottom trawl gear). This\ud has stimulated research that characterizes fish-habitat associations for use in\ud design of new survey methodology.\ud Using a combination of remote sensing, in situ observations, and spatial\ud analytical techniques, four benthic habitat classes were mapped for a large\ud rocky bank off the central Oregon coast known as Heceta Bank.\ud Observational data from human-occupied submersible and remotely operated\ud vehicle dives in the late 1980s, 2000 and 2001 were used to establish habitat\ud classes with specific substrate characteristics that have been statistically\ud shown to correlate with demersal fish distributions. The observational habitat\ud data was then extrapolated over the extent of a multibeam sonar survey\ud conducted in 1998 using quantitative parameters derived from high-resolution\ud bathymetric and backscatter imagery of the seafloor. The resultant map\ud predicts the locations of four habitat classes: Ridge-Gully, High-Relief Rock\ud (boulders, cobbles), Unconsolidated Sediment 1 (muds), and Unconsolidated\ud Sediment 2 (sands).\ud The main utility of the habitat map developed as part of the current study is\ud that it provides a context for analyses of a variety of spatial data. For instance,\ud habitat data provides one additional spatial component besides depth and\ud latitude that can be used to stratify catch per unit effort data from surveys and\ud commercial logbooks. Also, essential fish habitat for many demersal species\ud can now be identified in more detail. Finally, habitat data like those presented\ud here can aid in the design of marine reserves and protected areas by\ud providing a context for spatial analyses of data of ecological importance