Graduation date: 1979

The 36 samples collected with a 22-foot semi-balloon shrimp trawl at depths from 40 to 1,829 meters off the central coast of Oregon between July 1961 and June 1962 provided preliminary data on the distribution, species composition, and associations of benthic fishes with respect to depth and sediment type. Sixty-seven species of bottom fishes representing 21 families were collected; 86 percent of the total number of fishes was composed of specimens from the families Pleuronectidae, Scorpaenidae, and Bothidae. Four communities of benthic fishes were found off the central Oregon coast within the depth interval from 40 to 1 ,829 meters. They were characterized by two or three dominant species, depth, and average sediment type. Ninety-seven percent of the species occurring in the communities showed high abundance in only one community. Some species also demonstrated size segregation by communities. The total number of species collected in progressively deeper communities was 26 (42 to 73 meters), 31 (119 to 199 meters), 20 (594 to 1,143 meters), and 9 (1,383 to 1,829 meters). Therefore the highest number of speciesoccurred in the community on the outer continental shelf and upper slope, while the lowest number of species occurred at the extreme depths on the continental slope. The number of species found on the continental shelf and slope were similar. Species inhabiting the continental slope, however, usually occurred over greater depth ranges. A comparison of the catches of the 22-foot shrimp trawl and a 94-foot fish trawl indicated that the small trawl used in this study retained comparatively few large fishes or semi-pelagic species. Fishes of the genus Sebastodes were grossly undersampled and probably comprised a major portion of the fish population, especially between the depths of 183 to 547 meters. / Graduation date: 1968

Samples of benthic organisms off the coast of Oregon, taken from depths varying from 50 to 2900 meters, have been analyzed in terms of diversity at a given station, and similarity and ecological distance to other stations. Estimates of epifauna abundance were also made. In the analysis an important distinction is made between diversity, abundance, and variety indices; the three measures are considered independent pieces of information relevant to the ecological structure of the population of interest. Two types of sampling gear were used. Large epifauna were sampled with a beam trawl. Polychaetous infauna were sampled with an anchor-box dredge. The diversity index chosen is Simpson's index; the measures of similarity and ecological distance are related. These measures are preferred because of their ease in calculation and basic simplicity. In addition these measures may be interpreted as estimates of well-defined population parameters (as Simpson has pointed out) which have straightforward probabilistic interpretation. A valid measure of diversity is one piece of relevant information necessary for elucidating the sufficient parameters of ecological systems. Therefore the methodology presented has broad application to studies of population structure. / Graduation date: 1970