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
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/35180 |
| Date | 04 May 1994 |
| Creators | Toole, C. L. (Christopher L.) |
| Contributors | Markle, Douglas F. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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