Long-term variation and adaptive relationship between the life cycle parameters of the North-East Atlantic cod Gadus morhua (220.1Kb)

Long-term variation and adaptive

relationship between the life cycle parameters of the North-East

Atlantic cod Gadus morhua

by

Tretyak V.L.

The purposes:

- To study a long-term variation of the basic biological population para- meters of the North-East Atlantic cod, totality which determine the popula- tion development.

- To study the population mecha-

nism regulating the cod abundance

depending on intensive exploitation of

the stock.

min t

t k

exp 1

9 3 t

0 2

t 





 te

0

e ln 1

k t 1

t

s

1 t t

a exp 1

) 1 t ( S

3 t

5 . 0

s s

;

;

;

.

Material and methods

Long-term dynamics of the cod year classes growth rate (k) and maximum possible life span (t

).

0.045 0.050 0.055 0.060 0.065 0.070

1940 1960 1980 2000

Year class

k , year -1

22 24 26 28 30

te, year

kte

Maturity ogives of 66 cod year classes 0.0

0.2 0.4 0.6 0.8 1.0

3 6 9 12 15

Age, year

Portion of mature fish

а

0.06 0.08 0.10 0.12 0.14 0.16

1920 1940 1960 1980 2000 Year class

vs, year -1 2=0.92 ²_{=0.99 b}

0.06 0.08 0.10 0.12 0.14 0.16

0.40 0.50 0.60 0.70 0.80

Moving average F_5-10

Time trend of vs, year-1

R² = 0.79 c

0.06 0.08 0.10 0.12 0.14 0.16

0.40 0.50 0.60 0.70 0.80

Moving average F_5-10

vs, year -1 d² _{= 0.72}

-0.02 0.00 0.02 0.04

3.0 3.5 4.0 4.5 5.0

Moving average water temperature, ^oC

dvs, year-1

Variation of cod year classes maturation rate

a

0.45 0.55 0.65 0.75 0.85

1965 1975 1985 1995 Year

Moving average F 5-10, year-1

b ²=0.85 0.04

0.06 0.08 0.10 0.12 0.14 0.16

0.06 0.08 0.10 0.12 0.14

Moving average of v_s parameter of parental population, year ^-1

Parameter vs of year class, year -1

Variation of cod stock historic exploitation rate (a)

and cod year-class maturation rate depending on

average maturation rate of parental population (b)

2=0.95

0.06 0.08 0.10 0.12 0.14 0.16

1965 1975 1985 1995

Year class

Parameter vs, year -1

Approximation of v

-parameter by the regression equation with two independent variables –

historic exploiutation rate and moving average water temperature in 0-200 m layer of the

Murman Current main branch

Relationship between cod year-classes

maturation rate (v

) and maximum possible cod life span (t

) –(a), between their moving average by 21-th years –(b)

R²=0.99

24 25 26 27 28 29

0.08 0.10 0.12 0.14

Moving average of v_s-parameter, year ^-1

Moving average of te-parameter, year

b

2=0.75

22 24 26 28 30

0.05 0.07 0.09 0.11 0.13 0.15 Parameter v_s, year ^-1

Parameter te, year

a

Conclusions

- The numerical characteristics of the basic biological population parameters of the North-East Atlantic cod are changed after the mid of 1970s. The mathematical expectations of growth and maturation rates increased, life span decreased. Variances in the growth rate and the life span increased, rate of maturation decreased. The adaptive relationship between the maturation rate and life span individuals is reverse and statistically significant ( ²=0.75).

Conclusions

- Using a large historic series of observations (1930- 1997) it was shown that the main element in reproductiv strategy and cod population abundance dynamics, the rate of year-classes maturation (v_s), had a well-defined time logistic trend to increase (ρ²=0.92). That process

was conditioned by the historic stock exploitation rate in the period, which was close to the year-class life duration and preceding its appearance (ρ²=0.99). It promotes the increase in mature fish abundance and therefore is

aimed at diminishing the negative effect of rising morta- lity on the population abundance. Nevertheless the year- class maturation rate cannot increase to infinity. It has a threshold value outside the limit of which the collapse of the stock starts.The population mechanism of cod abun- dance regulation may be the biological basis of this

species stock management.