1 1

Buoyancy of eggs of Norwegian coastal cod from four locations along the coast

Erling Kåre Stenevik and Svein Sundby

2 2

Objectives

• Measure the neutral buoyancy of coastal cod eggs from different locations

• Relate this to ambient salinity structure

• Model the vertical distribution of the eggs

3 3

Sampling locations for parent fish

4 4

Methods

Broodstock collected during the spawning season in 2002 (2003)

40 families

Buoyancy experiments conducted in spring 2004

Porsanger (3 families)

Tysfjord (8 families)

Helgeland (4 families)

Øygarden (4 families)

Density gradient column used for buoyancy measurements

5 5

6 6

7 7

Salinity of neutral buoyancy

30.00

30.50

31.00

31.50

32.00

32.50

33.00

33.50

0 1 2 3 4 5

Group

Sal

init

y o

f n

eutr

al b

uo

yan

cy

Porsanger Tysfjord Helgeland Øygarden

8 8

0

50

100

150

200

250

29 30 31 32 33 34 35

Saltholdighet

Dy

p (

m)

0

2

4

6

8

10

12

14

16

18

20

29

29.4

29.8

30.2

30.6 31

31.4

31.8

32.2

32.6 33

33.4

33.8

34.2

34.6 35

Nu

mb

er o

f o

bs.

Porsanger

Buoyancy

Ambient salinity

9 9

0

50

100

150

200

250

29 30 31 32 33 34 35

Saltholdighet

Dyp

(m

)

0

5

10

15

20

25

30

35

40

45

29

29.3

29.6

29.9

30.2

30.5

30.8

31.1

31.4

31.7 32

32.3

32.6

32.9

33.2

33.5

33.8

34.1

34.4

34.7 35

Nu

mb

er o

f o

bs.

Tysfjord

Ambient salinity

Buoyancy

10 10

0

50

100

150

200

250

29 30 31 32 33 34 35

Saltholdighet

Dyp

(m

)

0

5

10

15

20

25

29

29.3

29.6

29.9

30.2

30.5

30.8

31.1

31.4

31.7 32

32.3

32.6

32.9

33.2

33.5

33.8

34.1

34.4

34.7 35

Nu

ber

of

ob

s.

Helgeland

Ambient salinity

Buoyancy

11 11

0

20

40

60

80

100

120

140

160

180

29 30 31 32 33 34 35

Saltholdighet

Dyp

(m

)

0

2

4

6

8

10

12

14

16

18

29

29.3

29.6

29.9

30.2

30.5

30.8

31.1

31.4

31.7 32

32.3

32.6

32.9

33.2

33.5

33.8

34.1

34.4

34.7 35

35.3

Nu

ber

of

ob

s.

Øygarden

Ambient salinity

Buoyancy

12 12

Coastal cod Porsangen

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120

Egg concentration (#/m3) at mean wind mixing

Dep

th (

m)

Coastal cod Tysfjord

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120

Egg concentration (#/m3) at mean wind mixing

Dep

th (

m)

Coastal cod Helgeland

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120

Egg concentration (#/m3)at mean wind mixing

Dep

th (

m)

Coastal Cod Dygarden

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120

Egg concentration (#/m3) at mean wind mixing

Dep

th (

m)

Modelled vertical distribution

13 13

Conclusions

• Differences in buoyancy and modelled vertical distribution of eggs from the four locations were found

• Eggs from Porsanger were on average lightest and distributed close to the surface

• Eggs from Tysfjord were on average heaviest with peak concentration at 50 m.

14 14

So what?

15 15

0 5 10 15 20 25 30 35 40 4563

65

67

69

71

73

75

77

79

Longitude

Latit

ude

Vikebø et al. (in prep.)