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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.)