The offshore Edgecumbe lava field, southeast Alaska: Geologic and habitat characterization of a commercial fishing ground

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Greene, H. G., O'Connell, V. M., Wakefield, W. W., & Brylinsky, C. K. (2007). The offshore Edgecumbe lava field, southeast Alaska: Geologic and habitat characterization of a commercial fishing ground. Special Paper - Geological Association of Canada, (47), 277-295.
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TitleThe offshore Edgecumbe lava field, southeast Alaska: Geologic and habitat characterization of a commercial fishing ground
AuthorsH. Greene, V. O'Connell, W. Wakefield, C. Brylinsky
AbstractThe application of geological and geophysical techniques in characterizing marine benthic habitats is increasing among fisheries biologists, marine geologists and fisheries managers. In this paper the results of a comprehensive sidescan sonar survey and seafloor observation/sampling program are applied to characterize fish habitats in a geologically complex volcanic region. Sidescan sonographs, interferometric bathymetric data, and in situ observations using the submersible Delta were used to identify and describe rockfish (Scorpaenidae, genus Sebastes) habitats of the continental shelf seaward of Kruzof Island in southeast Alaska. A major feature of this part of the continental shelf is the offshore Edgecumbe lava field. Mount Edgecumbe, a Holocene shield volcano, last erupted ca. 7000 years ago when it spread lava upon aflat glaciated surface and covered at least 600 km2 of seafloor and coastal plain west of Kruzof Island. The lava surface exhibits well-defined and little-eroded aa and pahoehoe lava, lobate lava fronts, compression ridges, collapsed lava tubes and volcanic cones that mark the distal end of Mount Edgecumbe's southwest rift. The presence of these features, along with the recovered vesicular basalt samplesftom the seafloor and the absence of pillow lava, suggests that the lava field was formed either terrestrially or in a shallow marine environment and, based on the depth of the outer limits of the field, has subsided at least 300 m. The offshore Edgecumbe lava field is defined as a marine benthic megahabitat that contains a variety of mesohabitats conducive to the habitation of rockfishes. The geologic features within this megahabilat give rise to mesohabitats that consist of pinnacles, caves, boulders, cobbles and pebbles, cracks and crevices, and ridges. The diversity and distribution of rockfish species appear to be related to mesohabitat type and depth, with the presence of suitably-sized refuge spaces a key to the occurrence of demersal rockfish. In boulder and ledge areas, such as those that occur around the pinnacles (volcanic cones), yelloweye rockfish (Sebastes ruberrimus), tiger rockfish (S. nigrocinctus), lingcod (Ophiodon elongatus), prowfish (Zaprora silenus) and sharpchin (S. zacentrus) are frequently present. On the pinnacles' crests where broken rock, ledges and platforms exist, the fish assemblage includes lingcod, quillback (S. maliger), Puget Sound (S. emphaeus) and young-of-the-year rockfishes. Similar assemblages of fish inhabit the caves and rubble-strewn floors of collapsed lava tubes. Elsewhere on the lavafield, rosethorn (S. helvomaculatus) and pygmy (S. wilsoni) rockfishes inhabit cracks and crevices in the lava flows and also occur in small boulder, cobble andpebble terranes. Compressional ridges with broken and angular boulders and slabs are frequented by yelloweye and tiger rockfishes. Pelagic rockfishes such as dusky (S. ciliattis), black (S. melanops) and yellowtail (S. flavidus) are found in schools and individually in areas of high relief, such as ridges and angular outcrops of rocks, and schools of pygmy rockfish and unidentified juvenile rockfishes inhabit most mesohabitats from pinnacles to cobble fields.
JournalSpecial Paper - Geological Association of Canada
Date2007
Issue47
Start page277
End page295
ISSN00721042
Subjectsbathymetric survey, continental shelf, demersal fish, habitat type, lava flow, observational method, seafloor mapping, sidescan sonar, species diversity, Alaska, Australasia, Bay of Plenty, Edgecumbe, New Zealand, North America, North Island, United States, Carpiodes cyprinus, Ophiodon elongatus, Scorpaenidae, Sebastes, Sebastes emphaeus, Sebastes flavidus, Sebastes helvomaculatus, Sebastes maliger, Sebastes melanops, Sebastes nigrocinctus, Sebastes ruberrimus, Sebastes wilsoni, Sebastes zacentrus, Zaprora silenus, Zaproridae
NoteRocks & Cores

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