Metamorphosis, growth, and settlement of Pacific sanddab (Citharichthys sordidus) to a continental shelf nursery, inferred from otolith microstructure Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6969z3314

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  • Processes of metamorphosis, settlement, and growth were examined in Pacific sanddab using field studies and otolith microstructure. This flatfish transforms at large sizes, has a gradual metamorphosis, and settles to a nursery on the middle continental shelf. Eye migration takes 3 months and "metamorphosis proper" which begins after completion of eye migration (CEM) takes an additional 1-2 months. Larvae at CEM ranged from 30-46 mm SL and were 125-224 d old. Coefficients of variation in length and age at CEM were 0.081 and 0.122, similar to flatfishes that transform at smaller sizes. Accessory primordia (AP) and an opaque region formed in the sagitta 14-49 d before CEM and 2-3 months before the start of the juvenile period. Depth stratified benthic surveys were conducted on the continental shelf and upper slope off central Oregon bimonthly in 1989 and in March 1990-1994. Peak settlement occurred in late fall and winter. Larvae initially landed on the upper slope but continued inshore to the middle shelf, a process that takes ~50-60 d. The nursery is centered at 80-119 m in winter and 50-99 m in summer. Abundance of settling Pacific sanddab on the upper slope in March 1989-1994 was strongly correlated to onshore Ekman transport during the preceding 30 d (r=0.91, P=0.013, n=6). Electron microprobe analysis revealed strong cross-otolith trends in concentrations of Sr, K, and P in Pacific sanddab and Dover sole, but trends were not related to settlement, thermal experience, or otolith and somatic growth. Margin concentrations of Cl and K differed among stations as little as 5-8 km apart, potentially indicating meso-scale patchiness. Patterns also imply long term cohesion of pelagic larvae, a surprising result given the 9 month to 2 year pelagic period of Dover sole. Time series of daily increment widths revealed ontogenetic, seasonal, and individual variation in otolith growth rate. Otolith growth rates were correlated with SST in 1992 and 1994, but were largely determined by timing of settlement. Otolith growth was synchronous among a small portion of each year class. Distinct growth histories acted as natural tags that allowed study of patch dynamics and settlement.
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