Th 1630 Marshall

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Trophodynamic effects on the maturation of Northeast Arctic cod C. Tara Marshall School of Biological Sciences University of Aberdeen

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0.0 0.2 0.4 0.6 0.8 1.0 1946 1956 1966 1976 1986 1996 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 Maturation of Northeast Arctic cod data for 1946-2001 from ICES Arctic Fisheries WG 2002

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Fisheries-induced evolution many fish stocks mature earlier than they did only a few decades ago there is some evidence that changes in maturation could be evolutionary Developmental threshold maturation triggered by the attainment of a critical size and/or level of surplus energy interannual variability in maturation can therefore result from differences in prey availability

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Objectives describe relationship between weight-at-age (body size) and maturity-at-age describe relationship between weight-at-length (girth) and maturity-at-length describe relationship between liver weight (stored energy) and maturity-at-length are these relationships impacted by environment (food + temperature)?

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Maturation of Northeast Arctic cod 1946-2001

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Weight-at-age vs. Maturity-at-age data for 1946-2001 from ICES Arctic Fisheries WG 2002 2.5 3.0 3.5 4.0 0.0 0.2 0.4 0.6 0.8 1.0 Age 7 3.0 3.5 4.0 4.5 5.0 5.5 0.0 0.2 0.4 0.6 0.8 1.0 Age 8 4 5 6 7 8 9 0.0 0.2 0.4 0.6 0.8 1.0 Age 9 6 8 10 12 0.0 0.2 0.4 0.6 0.8 1.0 Age 10 Weight (kg) Proportion mature

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2.5 3.0 3.5 4.0 0.0 0.2 0.4 0.6 0.8 1.0 Age 7 3.0 3.5 4.0 4.5 5.0 5.5 0.0 0.2 0.4 0.6 0.8 1.0 Age 8 4 5 6 7 8 9 0.0 0.2 0.4 0.6 0.8 1.0 Age 9 6 8 10 12 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 Age 10 Weight (kg) Proportion mature Weight-at-age vs. Maturity-at-age data for 1946-1979 and 1985-2001 plotted separately

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Wa vs. Ma two epochs: pre 1980 and post 1984

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Weight-at-age vs. Maturity-at-age Norwegian data only, data from 1980-1984 excluded 3000 3500 4000 4500 5000 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 Age 7 - Norway 4000 4500 5000 5500 6000 6500 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 Age 8 - Norway 4000 5000 6000 7000 8000 9000 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 Age 9 - Norway 5000 6000 7000 8000 9000 10000 11000 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 Age 10 - Norway Weight (g) Proportion mature

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2000 2500 3000 3500 4000 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 Age 7 - Russia 3000 3500 4000 4500 5000 5500 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 Age 8 - Russia 4000 5000 6000 7000 8000 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 Age 9 - Russia 5000 6000 7000 8000 9000 10000 11000 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 Age 10 - Russia Weight (g) Proportion mature Weight-at-age vs. Maturity-at-age Russian data only , data from 1980-1984 excluded

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1000 2000 3000 0.0 0.05 0.10 0.15 80 81 82 84 pre 1980 post 1984 Age 6 - Russia 2000 2500 3000 3500 4000 0.05 0.10 0.15 0.20 0.25 0.30 80 81 82 83 84 pre 1980 post 1984 Age 7 - Russia 3000 3500 4000 4500 5000 5500 0.2 0.4 0.6 80 81 82 84 pre 1980 post 1984 Age 8 - Russia Weight (g) Proportion mature synchronous increase in proportion mature occurred in 1984 across age classes year-effect rather than cohort-effect suggests that the abrupt shift is non-genetic in origin

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Wa vs. Ma Norwegian and Russian data both support two epochs; Russian data suggest transition in 1983 and 1984

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3000 3500 4000 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 72.5 cm 4000 4500 5000 5500 6000 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 82.5 cm 5500 6000 6500 7000 7500 8000 8500 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 92.5 cm 8000 9000 10000 11000 12000 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 102.5 cm Weight (g) Proportion mature Weight-at-length vs. Maturity-at-length age-based data converted with ALKs (Marshall et al. in press)

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Wl vs. Ml two epochs differ in girth; post 1984 data show that heavier fish have higher proportions mature for all lengths

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150 200 250 300 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 72.5 cm 200 250 300 350 400 450 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 82.5 cm 300 400 500 600 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 92.5 cm 300 400 500 600 700 800 900 0.0 0.2 0.4 0.6 0.8 1.0 pre 1980 post 1984 102.5 cm Liver weight (g) Proportion mature Liver Weight vs. Maturity-at-length Liver Weight = Weight-at-length X Liver Condition Index

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0 2000 4000 6000 8000 150 200 250 r2 p-value 0.25 0.0002 Capelin stock biomass (thou. t) Liver weight 72.5 cm (g) Effect of capelin on liver weight of cod data for 1946 to 2001

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Temperature effects on Liver weight vs. Maturity-at-length Ml = LWl + Temperature + LWl *Temperature

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Sources of variation in maturation of Northeast Arctic cod Two distinct epochs in cod growth and maturation; transition in 1984 Epochs can result from abrupt changes in hydrographic conditions (e.g., Baltic) or plankton production (Reid et al. 2003) Rapid and reversible shifts in maturation have been observed in other stocks (e.g., North Sea herring) First-order effect on maturation Capelin stock biomass determines stored energy which in turn impacts maturation of cod Food signal is amplified as more detailed bioenergetic indices are used to represent growth+condition

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Sources of variation in maturation of Northeast Arctic cod (cont’d) No effect of temperature (average July-Dec) on residual variation within epochs and age or length classes Long-term change towards earlier maturation can be explained without invoking genetic selection Future studies of genotypic selection should account for variability in feeding conditions when assessing role of genetic selection

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0 1000 2000 3000 4000 5000 6000 7000 8000 9000 1972 1975 1978 1985 1988 1991 1994 1997 2000 2003 Capelin biomass (thou. t) What are the implications of the recent reduction in capelin biomass for cod stock dynamics? Decrease in cod maturation and therefore SSB is possible in 2004

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