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This case study explores the Dover sole, a flatfish species found in muddy to muddy-sand habitats from Baja California to the Bering Sea, at depths ranging from 35 to 1400 m. It examines their feeding habits, which include polychaete worms, shrimp, and small bivalves, along with their winter spawning cycle from December to February. The study includes significant data from fishery landings, size and age compositions, as well as natural mortality rates. Insights on the stock trends and fishery management from 1910 to 2004 are detailed, highlighting changes in maturation and size retention functions over time.
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Case Study - Dover Sole • Range from Baja California to the Bering Sea. • On mud or muddy-sand, at 35 to 1400 m depths. • Feed on polychaete worms, shrimp, brittle stars, and small bivalves. • Winter spawning (December to February). • Planktonic larval stage lasts at least one year. • Gradual movement to deeper waters with growth. FW599 Winter 2008
US West Coast Dover Sole - Landings FW599 Winter 2008
Dover Sole – Sexual Dimorphism FW599 Winter 2008
Dover Sole – Fishery Size Composition FW599 Winter 2008
Dover Sole – Changes with Depth FW599 Winter 2008
Dover Sole – Changes in Mean Weight FW599 Winter 2008
Dover Sole – Small Fish are Discarded FW599 Winter 2008
Dover Sole – Recent Discard Data FW599 Winter 2008
Dover Sole - Assessment Data • Landings - 1910 to 2004 • Fishery length compositions - 1966 to 2004 • Fishery age compositions - 1981 to 2004 • Trawl logbook CPUE - 1978 to 1995 • Shelf survey biomass - 1980 to 2004 • Slope survey biomass - 1992 to 2004 • Survey length compositions • Observer Program discards - 2002 & 2003 FW599 Winter 2008
Dover Sole - Assessment Model Structure • Two fisheries - South (CA+S.OR) & North. • Separate slope surveys - AFSC (1992 to 2001) and NWFSC (1998 to 2004). • Fixed size-retention functions - Early (to 1980); Late (1986 to 2004); and Transition. The fisheries now retain smaller fish. • Fixed maturity-at-size functions - Early (to 1954); Late (1985 to 2004); and Transition. Maturation now occurs at smaller sizes. • Natural mortality fixed at 0.09/yr. FW599 Winter 2008
Dover Sole - Model Structure (continued) • Growth parameters estimated, but fixed relative variation (CV) in length-at-age. • Three periods for fishery selection L50s: Early (to 1979); Middle (to 1995); and Late. • Recruitment deviations from 1930. • Beverton & Holt stock-recruit curve with fixed steepness (0.8) and variability (0.35). • Reduced lambdas on length-at-age (0.1) and age composition (0.2) data. FW599 Winter 2008
Dover Sole – Estimated Stock Trends Fishery Lengths Fishery Ages Shelf Survey Slope Survey Trawl Logbook CPUE Available Data FW599 Winter 2008
Dover Sole – Fit to the Tuning Indices FW599 Winter 2008
Dover Sole – Fit to the Length Compositions Southern Fishery Females Pearson Residuals (Black=Neg.) Males FW599 Winter 2008
Dover Sole – Fit to the Age Compositions Southern Fishery Females Pearson Residuals (Black=Neg.) Males FW599 Winter 2008
Dover Sole – Estimated Selection Curves FW599 Winter 2008
Dover Sole – Likelihood Profile FW599 Winter 2008
Dover Sole – Recruits versus Spawners FW599 Winter 2008
Dover Sole – Random Starting Values FW599 Winter 2008
Dover Sole – Retrospective Analysis Data through 2005 through 2004 through 2003 through 2002 through 2001 FW599 Winter 2008
Dover Sole – Compared to Last Assessment FW599 Winter 2008
