Slide1: Trophodynamic effects on the maturation of Northeast Arctic cod C. Tara Marshall
School of Biological Sciences
University of Aberdeen
Slide2: 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
Slide3: 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
Slide4: 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)?
Slide5: Maturation of Northeast Arctic cod
1946-2001
Slide6: 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
Slide7: 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
Slide8: Wa vs. Ma two epochs: pre 1980 and post 1984
Slide9: 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
Slide10: 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
Slide11: 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
Slide12: Wa vs. Ma Norwegian and Russian data both support two epochs; Russian data suggest transition in 1983 and 1984
Slide13: 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)
Slide14: Wl vs. Ml two epochs differ in girth; post 1984 data show that heavier fish have higher proportions mature for all lengths
Slide15: 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
Slide17: 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
Slide18: Temperature effects on
Liver weight vs. Maturity-at-length Ml = LWl + Temperature + LWl *Temperature
Slide19: 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
Slide20: 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
Slide21: 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