Graduate Thesis Or Dissertation
 

Trophic adaptations and relationships of rockfishes (Sebastes spp.) of Oregon

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  • A comparative analysis of structures related to capture and processing of food, in 624 specimens belonging to 31 species of Sebastes of Oregon was made. The structures studied were the following: the tooth-bearing bones (premaxillary, dentary, vomer, palatine); the maxillary, angular, articular, parasphenoid and glossohyal bones; the lower limb of the first branchial arch and its gillrakers; the length of the intestine; number of pyloric caeca; and width of orbit. The mean values calculated formed gradual clines with only minor discontinuities. Overlap of standard deviations and ranges was considerable. Gillrakers showed four types according to the relationship of the length to width, and there is a general relationship of the type to mouth size, and in some, to relative length of intestine. Number and size of spinulae on gillrakers differ with gillraker type. Species with relatively long intestines have more pyloric caeca than those with short intestines. These are generally species that take a high proportion of crustaceans in the diet. Species with smaller relative eye size are generally planktivores, or are known to be diurnal in habit. Although a few species have distinctive features or specializations that alone or in simple combination can distinguish them, the overlap in trophic adaptation of the somewhat generalized predators is great. There is a continuum of change from planktiphagous to ichthyophagous, so that the genus as a whole, should be capable of taking advantage of a wide spectrum of prey over a wide latitudinal and considerable bathymetric range. Overlaps in diet must be common, but there is probably sufficient difference in trophic adaptation so that each species would be successful in a particular niche if food were in short supply.
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