US-GLOBEC NW Atlantic Georges Bank ProgramBroadscale cruises 1995-1999 (Jan-June)

Process cruised 1995, 97 and 99 (Mar-May)

Growth rate of <10,000 estimated from RNA/DNA and water temperature (Buckley et al. 2006)

Prey estimates (Buckley and Durbin 2006) and mortality rates (Mountain et al. 2003, submitted) from broad-scale surveys

Funding NSF and NOAA

Seasonal trends in mortality and growth of cod and haddock larvae on Georges Bank result in an optimal window for survival.

LJ Buckley, RG Lough and D MountainNOAA/NMFS Northeast Fisheries Science Center and the URI/NOAA CMER Program

Observed and predicted larval growth rates. Predicted values were from a GAM incorporating larval size and photoperiod. (Buckley et al. 2006)

Percentage of variability in observed growth of larval cod and haddock explained

Date and Size 61%

Factors contributing to the year effect: food, salinity, and density

48%Unexplained

29 %

Year10%

Haddock Cod

39%

13%

Cod

Haddock

Predicted and Observed Mortality Rate (d-1)

◊ Red-High Mortality (1995-96)

◊ Green-Low Mortality (1998-99)

Mortality = C – m1pp + m2pp3 + m3dumv

1997 (not shown) constant M in cod (mean 0.067) and decreasing M in haddock

Pre

dict

ed a

nd O

bser

ved

Mor

talit

y (d

-1)

0.00

0.05

0.10

0.15

0.20

0 30 60 90 120 150

rate

( d

-1)

0.00

0.50

1.00

1.50

2.00

M/G

Cod – Low Mortality and 1999 Growth

MM/G

G

-0.05

0.00

0.05

0.10

0.15

0.20

0 30 60 90 120 150

Year Day

rate

(d-1

)

0

2

4

6

M/G

M/G

G

M

M/G (right axis) is an index of stage-specific mortality and the rate of change in biomass.

In years with high mortality, M was always >G in young larvae.

In years with low mortality and high G, M< G for a period in March allowing the biomass of the cohort to increase.

Cod – High Mortality and 1995 Growth

0

20

40

60

0 10 20 30

Age (d)

Bio

mas

s (g

) Feb

March

April

May

Low Mortality-High Growth (1998-99)

0

20

40

60

0 10 20 30

Age (d)

Bio

mas

s

High mortality-Low Growth (1995-96)

0

20

40

60

0 10 20 30

Age (d)

Bio

ma

ss

(g

)

Constant Mortality-High Growth (1997)

Cod

In most years, the March and February cohorts fared better than later cohorts. In years with low M and high G, biomass of these early cohorts increased in the first 30 dph.

In 1997, the May cohort may have experienced an early increase in biomass.

Trends in Biomass

Norway Cod Transition Size

1.0

10.0

100.0

1000.0

10000.0

0 30 60 90 120 150

Year Day

Prot

ein

(ug)

@M

=GCod - Transition Size M=G

1

10

100

1000

10000

0 30 60 90 120 150

Year Day

Pro

tein

(u

g)

@M

=G

Georges Bank

Using the same G and M models with the photoperiod schedule for Norway results in a much narrower optimum window for Atlantic cod larvae.

Norway

Conclusions

Strong seasonal trends in G and M interact to determine the change in biomass of cohorts.

The fastest growing cohorts, those hatched in May, are rapidly lost to predators in most years.

In years with abundant prey early in the year, cohorts hatching in February and March experience lower mortality and can increase rapidly in biomass. These early cohorts may ultimately make up the bulk of the survivors.

In agreement with the conclusions above, otolith microstructure analysis of haddock surviving to the fall in the Gulf of Maine (Lapolla and Buckley 2005) and the North Sea (Wright and Gibb 2005) indicate strong negative selection on hatch date.

Our data support Pope et al’s (1995) “optimal fish strategy” in a seasonally-perturbed, size spectrum. Successful cod and haddock hatch ahead of the peak abundance of prey, reaching a large size before being overtaken by the wave of abundant predators.