Graduate Thesis Or Dissertation
 

Video on the rocks : use of a video lander platform as a survey tool for a high-relief nearshore temperate rocky reef

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  • The nearshore waters off the Oregon coast (< 73 meters) are a region of high productivity and economic value, with a variety of habitats that include rock outcrops. Temperate reef habitats are important to many commercially important fishes inhabiting the Pacific coast, including canary rockfish (Sebastes pinniger) and yelloweye rockfish (Sebastes ruberrimus), which are currently listed as "overfished" by the Pacific Fishery Management Council. Along the Pacific coast of North America, nearshore rocky reefs have been designated as essential fish habitat (EFH), while comprising approximately just seven percent of Oregon's territorial sea. Despite this EFH designation, the use of visual (SCUBA, remotely operated vehicles (ROVs), human occupied vehicles (HOVs)) and non-visual (bottom trawl) survey methods within this region has been infrequent and scattered, providing limited information on species-habitat associations and species assemblages within nearshore waters. It is logistically difficult and costly to survey nearshore reefs. The factors that have led to the paucity of surveys include the depth (too deep for SCUBA surveys but too shallow for larger survey vessels), high seas limiting available days for field work, and the high-relief nature of the habitat (precluding the use of bottom trawls). In an effort to better understand species-habitat associations and community structure of Oregon's nearshore reefs, an autonomous underwater drop-camera termed the "video lander" was employed at the Three Arch Rocks reef, a nearshore reef off of Oceanside, Oregon. Video lander footage was used to identify and groundtruth habitat types, as well as species assemblages over two distinct seasons: spring/summer (n=272) and winter (n=108). Many species-habitat associations were statistically significant: yelloweye rockfish (large boulder p<0.0073), canary rockfish (small boulder p<0.0006), kelp greenling (Hexagrammos decagrammus) (bedrock outcrop p<0.0162), and quillback rockfish (Sebastes maliger) (large boulder p<0.0016). Summer and winter surveys revealed similar habitat associations and distributions for these species. I found no significant difference in species composition between the northern and southern regions of the reef (Bray-Curtis dissimilarity index (BCDI) = 71.71, ANOSIM p>0.1447), but a significant difference between spring/summer and winter seasons was identified on the outer section of the reef, due to the presence of spotted ratfish (Hydrolagus colliei) in the winter (BCDI =76.41, ANOSIM p < 0.0155). My study shows that data provided by the video lander can fill existing gaps in our understanding of nearshore distribution and habitat associations of temperate rocky-reef fishes off the Oregon coast.
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