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Ontogeny and metamorphosis in the Dover sole (Microstomus pacificus) : a description of the early life history stages, with comments on the sister-group relationship between Microstomus and EmbassichthysHarris, Phillip M. 29 May 1992 (has links)
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
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Settlement, distribution, growth, and mortality of juvenile dover sole (Microstomus pacificus) off northern OregonToole, C. L. (Christopher L.) 04 May 1994 (has links)
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
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