The early life history stages and metamorphosis in Dover sole (Microstomus pacificus) are described from 201 larvae and juveniles. Unlike other pleuronectids, with the possible exception of the deep-sea sole (Embassichthvs bathvbius), initial migration of the left eye is not associated with metamorphosis or transition from plankton to benthos. The left eye exhibits a stasis during its migration, so that premetamorphic larvae are optically asymmetrical while planktonic. Seven characters are used to quantify the progress of metamorphosis: completed eye migration, dorsal fin position, dentition, pectoral fin development, condition of posterior process of coracoid, pigmentation, and elongation of the intestine into a secondary body cavity. Other characters associated with metamorphosis are reduction in body depth associated with reductions in lengths of neural and hemal spines and associated dorsal- and anal- fin pterygiophores, decreasing interorbital distance, increasing right eye diameter and right premaxilla length, and development of body scales. Metamorphosis appears to require 9- 11 or 12 months to complete. The planktonic period of premetamorphic and metamorphic larvae is about 18-24 months. Metamorphic larvae appear to move inshore into shallower water as metamorphosis progresses. Settlement occurs from about December to April, primarily from January to March. One of the earliest phylogenetic hypotheses about the intergeneric relationships of the pleuronectid genera Microstomus, Embassichthys, Glyotocephalus, and Tanakius was by Norman (1934), who considered Microstomus plus Embassichthvs and Glyotocephalus plus Tanakius to be sister groups. An alternative hypothesis by Richardson (1981) suggested that Embassichthvs larvae resembled larvae of Glyptoceohalus and Tanakius based on a "leptocephaluslike" body shape, and that Microstomus was the primitive sister group of these three genera because of its dorsoventrally deepened body shape. In order to evaluate Richardson's hypothesis of sister group relationships based on body shape, I examined morphological characters associated with eye migration and metamorphosis, and changes in body shape during ontogeny from post-flexion larvae through benthic juveniles. Richardson's-character of a moderate "leptocephalus-like" body shape is an artifact of the paucity and small size range of larvae available for her examination. The body shape of larger Embassichthvs larvae is also dorsoventrally deepened and the larvae appear to undergo changes in body shape during metamorphosis similar to Microstomus. Three synapomorphies that support Norman's hypothesis of an Embassichthys plus Microstomus sister group relationship are dissociation of initial eye migration with metamorphosis, a stasis during eye migration in premetamorphic larvae, and a retention of a larval-like appearance to the eyes of newly settled specimens. / Graduation date: 1993

Demographic characteristics of juvenile Dover sole (Microstomus pacificus) were examined in relation to physical and biotic factors to develop a hypothesis explaining annual variations in recruitment. Surveys were conducted along the Oregon continental shelf at depths between 50-400 m bimonthly during 1989 and annually (in March) between 1990 and 1993. To determine settlement timing, growth, and mortality, daily growth increments were validated, as was position of the first post-settlement annulus. A method of estimating precision of otolith elemental composition with the electron microprobe was developed; otolith microstructure and microchemistry were used to identify a landmark associated with settlement. Mean density of 0-group settlers varied annually, with 1989 and 1990 high, 1991 and 1992 low, and 1993 intermediate. 0-group abundance was correlated with fall offshore divergence one year before settlement and with southward geostrophic velocity during the summer before settlement. These conditions may be related to production of prey available to pelagic larvae. Density of 0-group Dover sole was highest between 100-119 m, but deeper areas were also utilized in years of highest abundance. Density was not correlated with spawning stock biomass or density of older juveniles. It was correlated with rex sole (Glyptocephalus [Errex] zachirus) density. Growth rate was positively correlated with mean April-October upwelling and was not related to density or mortality of Dover sole. First-year mortality was positively correlated with early settlement of 0-group larvae, possibly due to an advantage of settling and migrating to the primary nursery area well in advance of the spring transition. A multiple regression model predicting density of 1-group Dover sole from three physical environmental factors was applied to an independent time series of Dover sole "age-5" recruitment estimates (Turnock and Methot 1992). The model was a poor predictor of annual recruitment to fisheries but a good predictor of trends based on five-year running averages. Results suggest that multi-year trends in Dover sole recruitment to fisheries can be explained by a small set of density-independent physical factors. / Graduation date: 1995