Global warming and fish stocks: Global warming and fish stocks: Winter spawning of Baltic sprat Winter spawning of Baltic sprat ((Sprattus sprattusSprattus sprattus) as a possible ) as a possible

future scenariofuture scenario

Gerd Kraus1, Volker Mohrholz3, Gerd Kraus1, Volker Mohrholz3, Rüdiger Voss1, Miriam Dickmann3, Hans-Harald Hinrichsen1, Rüdiger Voss1, Miriam Dickmann3, Hans-Harald Hinrichsen1, Christian Möllmann2, Friedrich W. Köster2, Dietrich Schnack1, Christian Möllmann2, Friedrich W. Köster2, Dietrich Schnack1,

Jens-Peter Herrmann4, Andreas Lehmann1, Axel Teming4, Jens-Peter Herrmann4, Andreas Lehmann1, Axel Teming4, Daniel Stepputtis1, Jürgen Alheit3Daniel Stepputtis1, Jürgen Alheit3

1Leibniz Institute of Marine Sciences, Kiel, Germany1Leibniz Institute of Marine Sciences, Kiel, Germany2Danish Institute for Fisheries Research, Charlottenlund, Denmark2Danish Institute for Fisheries Research, Charlottenlund, Denmark3Institute for Baltic Sea Research, Rostock-Warnemünde, Germany3Institute for Baltic Sea Research, Rostock-Warnemünde, Germany4Institute of Hydrobiology and Fishery Science, Hamburg, Germany4Institute of Hydrobiology and Fishery Science, Hamburg, Germany

THE BALTIC SEATHE BALTIC SEA

100 150 200500

GotlandBasin

GdanskDeep

BornholmBasin

m

to North Sea

Study area

ApproachApproach

•Resolve the timing of gonadal maturation Resolve the timing of gonadal maturation and spawning of Bornholm Basin sprat at and spawning of Bornholm Basin sprat at high resolution and covering the full high resolution and covering the full annual reproduction cycleannual reproduction cycle

•Parallel investigation of egg and larval Parallel investigation of egg and larval abundance in the field to resolve egg and abundance in the field to resolve egg and larval productionlarval production

•Corresponding 3D-hydrographic measure-Corresponding 3D-hydrographic measure-ments to resolve ambient conditions for ments to resolve ambient conditions for the spawning stock, eggs and larvae the spawning stock, eggs and larvae

SamplingSampling

Temporal coverage:Temporal coverage:

•April 2002 to April 2003April 2002 to April 2003

•14 Surveys in 2-8 week intervals14 Surveys in 2-8 week intervals

Fish:Fish:

•4 Hydroacoustic Transects4 Hydroacoustic Transects

•Min. 2 trawl hauls per ICES square Min. 2 trawl hauls per ICES square (~15nm horizontal resolution)(~15nm horizontal resolution)

•10-20 Sprat sexed & maturity staged 10-20 Sprat sexed & maturity staged per haul and cmper haul and cm

•Calculation of weighted average date Calculation of weighted average date specific sex ratios and maturity stagesspecific sex ratios and maturity stages

Ichthyoplankton:Ichthyoplankton: •45 Bongo net stations (500 µm)45 Bongo net stations (500 µm)

•~10nm grid point distance~10nm grid point distance

•Stage specific abundanceStage specific abundance values for eggs and larvaevalues for eggs and larvae

Hydrography:Hydrography:•Time series measurementsTime series measurements -Dars Sill and Central Bornholm Basin-Dars Sill and Central Bornholm Basin

•Synoptic 3D-hydrographic Synoptic 3D-hydrographic measurementsmeasurements -Vertical resolution <1m-Vertical resolution <1m -Horizonal resolution ~ 10 nm-Horizonal resolution ~ 10 nm

Reproduction cycle of Baltic sprat IReproduction cycle of Baltic sprat I

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Sp

awn

ing

inte

nsi

ty

Av

aila

ble

en

erg

y

Te

mp

era

ture

Sprat gonadal maturation Sprat gonadal maturation cycle during 2002 / 2003cycle during 2002 / 2003

•May/June is peak spawning May/June is peak spawning time in 2002 time in 2002

•Spawning ceased in early Spawning ceased in early August 2002August 2002

•Spawning restarted in Spawning restarted in November 2002November 2002

•Second minor spawning peak Second minor spawning peak in January 2003in January 2003

•In April 2003 spawning In April 2003 spawning activity as high as in May/June activity as high as in May/June 20022002P

ropo

rtio

n in

sp

aw

nin

g c

ond

itio

n

0,0

0,2

0,4

0,6

0,8

1,0

0,0

0,2

0,4

0,6

0,8

1,0

females

males

2002 2003

Mar

May

July

Sep

t

No

v

Jan

Mar

Temperature time series in the Temperature time series in the Central Bornholm BasinCentral Bornholm Basin

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Tem perature [°C ]

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

Dep

th [m

]

0123456789101112131415161718192021

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

O xygen [m l/l]

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

Dep

th [m

]

- 3

- 2

- 1

0

1

2

3

4

5

6

7

8

9

1 0

1 1

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

-1

0

1

2

3

4

5

Te

mp

era

ture

[°C

]

annual temperature minimum in the intermediate layer

Se

a s

urf

ace

te

mp

era

ture

[°C

]

14

15

16

17

18

19

20

21 SST August

54° 42.00‘ N 12° 42.00‘ E 01.02. 2002 - 01.08. 2003

TS patterns at the Darss SillTS patterns at the Darss Sill

Tem perature [°C ]

-20

-10

0

Dep

th [m

]

0123456789101112131415161718192021

1.02. 1 .04. 1 .06. 1 .08. 1 .10. 1 .12. 1 .02. 1 .04. 1 .06. 1 .08.2002 2003

Salin ity [ISS78]

-20

-10

0

Dep

th [m

]

1 .02. 1 .04. 1 .06. 1 .08. 1 .10. 1 .12. 1 .02. 1 .04. 1 .06. 1 .08.2002 2003

A CB

Distribution of the youngest egg Distribution of the youngest egg stage during November 2002stage during November 2002

40 m

55°00´

56°00´

N

15°00´ 16°00´ 17°00´

20 m

55°30'

54°30'

E

20 m

60 m

80 m

40 m

5°C

6°C

7°C

8°C

9°C

10°C

11°C

12°C

13°C

•Temperature surface Temperature surface derived from maximum derived from maximum temperaturestemperatures

•No eggs in areas with max. No eggs in areas with max. temperatures below 12°Ctemperatures below 12°C

•Majority of sprat distributed Majority of sprat distributed in >11°C layerin >11°C layer

Hydroacoustic Abundance

Tem

pera

ture

[°C

]

De

pth

[m

]

55°00´

56°00´

N

15°00´ 16°00´ 17°00´

20 m

55°30 '

54°30 '

E

20 m

40 m

80 m

40 m

2°C

3°C

4°C

5°C

6°C

7°C

8°C

9°C

10°C

11°C

Distribution of the youngest egg Distribution of the youngest egg stage during January 2003stage during January 2003

•Uneven egg distribution, Uneven egg distribution, larger abundances on the larger abundances on the southern and south-eastern southern and south-eastern slopes of the Basinslopes of the Basin

•No eggs in areas with max. No eggs in areas with max. temperatures below 7°Ctemperatures below 7°C

•Majority of sprat distributed Majority of sprat distributed in >6°C layerin >6°C layer

De

pth

[m

]

Tem

pera

ture

[°C

]

Hydroacoustic Abundance

55°00´

56°00´

N

15°00´ 16°00´ 17°00´

20 m

55°30'

54°30'

E

20 m

60 m

80 m

40 m

0.5°C

1.5°C

2.5°C

3.5°C

4.5°C

5.5°C

6.5°C

7.5°C

Distribution of the youngest egg Distribution of the youngest egg stage during March 2002stage during March 2002

•Largest egg abundances in Largest egg abundances in the southern Central Basinthe southern Central Basin

•No eggs in areas with max. No eggs in areas with max. temperatures below 6.0°C temperatures below 6.0°C

•Temperatures below 3-4 °C Temperatures below 3-4 °C avoided by spratavoided by sprat

•Majority of sprat distributed Majority of sprat distributed in >6°C layerin >6°C layer

Hydroacoustic Abundance

Tem

pera

ture

[°C

]

De

pth

[m

]

Sprat egg abundance: Seasonal Sprat egg abundance: Seasonal dynamics 2002 / 2003dynamics 2002 / 2003

Date

1.1.02 1.3.02 1.5.02 1.7.02 1.9.02 1.11.02 1.1.03 1.3.03

Egg

abu

ndan

ce [n

/m²]

0

10

20

30

40

50

100

110

120

130

140

150

Egg stage IEgg stage IIEgg stage IIIEgg stage IV

• Peak spawning 2002 in mid April Peak spawning 2002 in mid April (150 eggs Ia/m²)(150 eggs Ia/m²)

•Spawning ceased by mid July 2002 Spawning ceased by mid July 2002 (0.2 eggs Ia/m²)(0.2 eggs Ia/m²)

•Spawning restarted in November Spawning restarted in November 2002 (1.2 eggs Ia/m²), reached 4.5 2002 (1.2 eggs Ia/m²), reached 4.5 eggs Ia/m² by mid January 2003eggs Ia/m² by mid January 2003

•Contribution of winter spawning Contribution of winter spawning to annual egg production is to annual egg production is negligiblenegligible

•Early spawning season in 2003 Early spawning season in 2003 (140 eggs Ia/m² in mid March)(140 eggs Ia/m² in mid March)

2002 2003

Sprat larval abundance and feeding: Sprat larval abundance and feeding: Seasonal dynamics 2002 / 2003Seasonal dynamics 2002 / 2003

Date

1.1.02 1.3.02 1.5.02 1.7.02 1.9.02 1.11.02 1.1.03 1.3.03

Larv

al a

bund

ance

[n/m

²]

012345

10

20

30

40

Feed

ing

Larv

ae [%

]0

5

10

15

20

25

30

35

40

452002 2003 • Peak larval abundance Peak larval abundance

2002 in May (45 larvae/m²)2002 in May (45 larvae/m²)

•Winter spawning yielded Winter spawning yielded low larval abundance (0.5 – low larval abundance (0.5 – 1.0 larvae/m²)1.0 larvae/m²)

•No feeding in March 2003No feeding in March 2003

•Low larval abundance Low larval abundance combined with low feeding combined with low feeding intensity in winter intensity in winter 2002/20032002/2003

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Reproduction cycle of Baltic sprat IIReproduction cycle of Baltic sprat IIS

paw

nin

g in

ten

sity

Av

aila

ble

en

erg

y

Te

mp

era

ture

?

Seasonal condition dynamics Seasonal condition dynamics of sprat 2002 / 2003of sprat 2002 / 2003

•Average Weight at mean length Average Weight at mean length during spawning time during spawning time considerably higher in 2003 considerably higher in 2003

•More More PseudocalanusPseudocalanus available in available in winter/spring 2003winter/spring 2003

Jan Feb March April

Ab

un

dan

ce [

(n/m

²)/1

000]

0

5

10

15

20

25 2002

2003

Pseudocalanus C4-Adult

Date1.3.02 1.6.02 1.9.02 1.12.02 1.3.03 1.6.03

Weight at mean length

9,0

9,3

9,6

9,9

10,2

10,5

10,8

11,1

11,4

11,7

12,0

12,3

12,6

Mean Apr-Jul

Mean Apr-Jul

[g]

ConclusionsConclusions

•Sprat winter spawning, a possible effect of the 2002 Sprat winter spawning, a possible effect of the 2002 warm summer inflow, is evidenced by maturity and egg warm summer inflow, is evidenced by maturity and egg abundance data abundance data

•The contribution of winter spawning to annual egg and The contribution of winter spawning to annual egg and larval production is negligible larval production is negligible

•A possible depletion of energy reserves due to winter A possible depletion of energy reserves due to winter spawning could be compensatedspawning could be compensated

•The sprat spawning season started earlier in 2003 than The sprat spawning season started earlier in 2003 than in 2002 in the remaining warm summer inflow waterin 2002 in the remaining warm summer inflow water

• The high condition and early spawning in 2003 may be The high condition and early spawning in 2003 may be an effect of increased an effect of increased PseudocalanusPseudocalanus abundance in abundance in winter spring 2002/2003winter spring 2002/2003

• Winter spawning may be critical to sprat reproduction Winter spawning may be critical to sprat reproduction under food limited winter/spring situationsunder food limited winter/spring situations

Thank you for your attention! Thank you for your attention!