1. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn What do we know about sprat??? - A survey through recent (German) research Material supplied by Gerd Kraus gkr@difres.dk Technical University of Denmark National Institute of Aquatic Resources

2. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn EU-funded Baltic CORE (Cod recruitment in the Baltic) and STORE (Environmental and fisheries influences on fish stock recruitment in the Baltic Sea) projects: -stock reproductive potential (viable EP) -Early life stages & Hydrography -Feeding, growth, survival -IBM modeling -Preator-prey interactions -Recruitment modelling & management aspects The German Globec Project (Trophic Interactions between Zooplankton and Fish under the Influence of Physical Processes) focussed on: -sprat & (herring) -copepods as key prey species -experiments, process studies, field sampling, process- to 3-D ecosystem modeling -Analyses restricted to Globec years (2002-2005) German Science Foundation funded project “Resolving Trophodynamic Consequences of Climate Change”targets sprat in the Baltic and North Sea: -time series analyses -Experiments; Process models -Coupled Tropho-Hydrodynamic modeling

3. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn 6 years Funded for 6 years (2002 – 2007) 8 8 Institutions (incl. Difres) 11 11 sub-projects 80 80 scientists and technicians 12 12 PhD students 13 13 student projects (diploma) 48 48 cruises in Baltic and North Sea 736 736 days at Sea German Globec German Bight Bornholm Basin

4. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Background / Hypotheses Adult reproduction biology and distribution Early life stage biology and relevance of early life processes for recruitment Modeling approches -Hydrodynamic -Ecosystem -IBM -Coupling

5. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Stock-size and recruitment of Baltic sprat Strong increase in stock size in early 1990s Change to higher mean and higher variability in recruitment

6. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Critical stages for recruitment Larval stage is important during recruitment process ! 0.320-groupLarval abundance 0.81*Larval abundanceEgg production 3 0.82*Egg production 3Egg production 1 0.66*Egg production 1SSB r2r2 Variable 2Variable 1

7. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn length class [cm] proportion females overall mean <11cm Simple model >11cm Adult reproduction biology – sex ratio

8. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn age group 1 high variable age group 2 in general more than 90% mature with some exceptions Adult reproduction biology – maturity

9. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Adult reproduction biology – maturity Good correlation between proportion mature age 1 with mean water temperature below halocline R = 0.75 P < 0.05

10. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Adult reproduction biology - fecundity - Sprat is an indeterminate spawner, consequently only batch fecundity can be estimated -Relative fecundity (oocytes per g female and batch) is independent of fish size as for Baltic cod, but … -There are significant differences in batch fecundity within a season -There are significant differences between spawning grounds - There are significant differences between years

11. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Multiple Regression Model: Dependent variable: y = mean batchsize per 0,5cm length class Independent variables: –x 1 = length –x 2 = mean water temperature r² = 0,82 p<0,05 y = -4988,36 + 335,70 * x 1 + 358,31 * x 2 + ε Adult reproduction biology - fecundity

12. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn 04/2002 06/2002 05/2002 01/2003 11/2002 07/2002 Adult sprat - horizontal distribution Triggered by spawning/feeding migrations and modulated by temperatures Large scale changes in distribution not understood!

13. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Adult sprat - vertical distribution Relevant environmental factors: T, O Limits: ~5°C, ~1ml/l O2; however derived from few observations Impact on diurnal vertical migration patterns! April 2002 Mai 2002

14. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Adult sprat - vertical distribuition model Model based on Copepod model introduced by Neumann & Fennel (2006) Diurnal vertical migrations behaviour parameterised! 4 variables: Temperature, oxygen, light, vertical temperature gradient

15. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Test against observed data possible, however needs to be tested and adapted outside spawning time! Adult sprat - vertical distribuition model

16. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Early life stages - Egg survival Survival rates account for temerature and oxygen Cold Winters! Sprat eggs like it warm!!!

17. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Up to 20% per day of sprat EP lost early in the season Herring Sprat Eggs per stomach Total consumption Daily production Proportion eaten Daily production (n*10 -9 *d -1 ) Consumption (n*10 -9 *d -1 ) Early life stages - Egg survival

18. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Early life stages - larval distribution Recent period – May 1998, May 1999, April 2000, June 2002 Ontogenetic differences in vertical distribution

19. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Night – Day Early life stages - larval distribution Behavioural changes from late 1980*s to most recent period! Early period: Diurnal migration Recent period: No migration

20. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Early life stages- larval distribution - feeding Larvae feeding mainly during day-time! Switch in main prey species when switching migration behaviour?

21. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Acartia spp. dominant prey 2002 and 1989! Gut contentPrey selection Early life stages- larval distribution - feeding

22. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Acartia bifilosa, Acartia longiremis, Temora longicornis, Early stages of Pseudocalanus acuspes Oithona similis, late stages of Pseudocalanus acuspes Thermocline Halocline Oxygen depletion zone Hatch of yolk-sac larvae Upward migration No migraton Diurnal vertical migration, crossing the thermocline However, no switch in diet observed between periods, reasons unclear! Early life stages- larval distribution - summary

23. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Beprobung der juvenilen Sprotten 18.-23.10. Birthdate backcalculation from survivor otholiths Early life stages - growth & survival

24. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Early life stages - growth & survival

25. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Fig.3: Temporal overlap between larval abundance and back-calculated hatch date distributions of YoY sprat caught in October 2002 in the Central Baltic Sea. Larval abundance was calculated from stage1 egg abundance in the Bornholm Basin adjusted for temperature-dependent (45-60m) duration times from stage1 to hatch. YoY sprat sampling 18.-23.10. Fig.3: Temporal overlap between larval abundance and back-calculated hatch date distributions of YoY sprat caught in October 2002 in the Central Baltic Sea. Larval abundance was calculated from stage1 egg abundance in the Bornholm Basin adjusted for temperature-dependent (45-60m) duration times from stage1 to hatch. YoY sprat sampling 18.-23.10. Fig.3: Temporal overlap between larval abundance and back-calculated hatch date distributions of YoY sprat caught in October 2002 in the Central Baltic Sea. Larval abundance was calculated from stage1 egg abundance in the Bornholm Basin adjusted for temperature-dependent (45-60m) duration times from stage1 to hatch. YoY sprat sampling 18.-23.10. Fig.3: Temporal overlap between larval abundance and back-calculated hatch date distributions of YoY sprat caught in October 2002 in the Central Baltic Sea. Larval abundance was calculated from stage1 egg abundance in the Bornholm Basin adjusted for temperature-dependent (45-60m) duration times from stage1 to hatch. YoY sprat sampling 18.-23.10. 5°C untere Temperatur- toleranz (Nissling 2004) Early life stages - growth & survival

26. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn  Good feeding conditions for small larvae eary in the season  Bad feeding conditions late in the season Early born Late born Small larvae  High abundance of copepodite stages at main spawning season  Bad feeding conditions for late born medium sized larvae Medium larvae  Bad feeding conditions for early born large larvae  High abundance of adulte copepods for late born large larvae! Large larvae Early life stages - growth & survival

27. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Survival index of larvae born late (June) higher than for early born larvae Confirms results from prey fieldanalyses & juvenile otholith analyses! Early life stages - growth & survival

28. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn 3D hydrodynamic model 3D-primitive equation model Grid distance 10 km 20 vertical levels Lagrangian transport module advection & diffusion Ecosystem Model Phytoplankton groups : 2 Zooplankton groups : 2 Nutrient cycles : 3 IBM sprat eggs & larvae 3-D transport, turbulence, temperature, salinity … 3-D transport, turbulence 3D-temperature, turbulence, light 3D-location3D-prey field IBM development – North Sea

29. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn START Next Time Step Egg ? Egg Development =f(T) yes no Yolk sac Development =f(T) yes Yolk Sac ? no Growth (+ or -) ENERGY LOSS = f (larval size, temperature, foraging...) Assimilation & Digestion Active Metabolism Routine Metabolism Day? no yes ENERGY GAIN = f (food, larval size, temperature, light) Prey Consumed? (limited by C max ) Forage Consumption =f(Encounter Rate (ER) Capture Sucess (CS) Handling Time (HT)) Mortality = f (W/L) no yes Egg Development =f(T) Temperature ( °C ) 0246810121416182022 Development rate ( % d -1 ) 0 10 20 30 40 50 60 70 North Sea f(T)=1.5133*T 1.23 Baltic Sea f(T)=3.925*T 0.63 Temperature dependent egg development

30. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn START Next Time Step Egg ? Egg Development =f(T) yes no Yolk sac Development =f(T) yes Yolk Sac ? no Growth (+ or -) ENERGY LOSS = f (larval size, temperature, foraging...) Assimilation & Digestion Active Metabolism Routine Metabolism Day? no yes ENERGY GAIN = f (food, larval size, temperature, light) Prey Consumed? (limited by C max ) Forage Consumption =f(Encounter Rate (ER) Capture Sucess (CS) Handling Time (HT)) Mortality = f (W/L) no yes Yolk sac Development =f(T) Temp vs development rate % D-1 x column 1 vs y column 1 Temperature ( °C ) 2468101214161820 Yolksac depletion rate ( % day -1 ) 4 6 8 10 12 14 16 18 Temperature-dependent yolksac depletion North Sea f(T)=0,378*T 1.32 Baltic Sea f(T)= 1.76*T 0.77

31. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn START Next Time Step Egg ? Egg Development =f(T) yes no Yolk sac Development =f(T) yes Yolk Sac ? no Growth (+ or -) ENERGY LOSS = f (larval size, temperature, foraging...) Assimilation & Digestion Active Metabolism Routine Metabolism Day? no yes ENERGY GAIN = f (food, larval size, temperature, light) Prey Consumed? (limited by C max ) Forage Consumption =f(Encounter Rate (ER) Capture Sucess (CS) Handling Time (HT)) Mortality = f (W/L) no yes Foraging success Temperature-dependent eye pigmentation/functional jaws Temperature (°C) 2468101214161820 Time (days post-hatch) 2 4 6 8 10 12 14 16 18 20 Baltic Sea f(T)=23.268*e (-0.116*T) North Sea Yolk Sac ? no

32. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Yolk Sac? Growth (+ or -) Advection (x, y, z, t) Mortality = f (W/L) Next Time Step ENERGY GAIN = f (food, larval size, & temperature) START no yes no ENERGY LOSS = f (larval size, temperature, foraging) Day? Prey Ingested? (limited by I max ) (Eqs. 6 & 10) Forage (encounter rate) = f (prey size, density) (Eqs. 5, 7, 8, 9) Assimilation & Digestion (Eqs. 1 & 4) Active Metabolism (Eq. 3) Routine Metabolism (Eq. 2) yes AE = 0.7(1-0.3e -0.003(W – Wmin) ) where Wmin – weight at hatch M R = 0.093W 0.8 2.57 (T-8)/10 M A = k M R G DAY = I AE (1-0.30) – M A I = SP  N i p i w i where w i – weight of prey type i I MAX = 2.56 W 0.795 1.90 (T-12)/10 N i = S RA p i H where S = 0.776 L 1.07 RA =  /2 RD 2 RD = PL / ( 2 tan(  /2)) where  – minimum visual angle  = 0.0167 e (9.14 – 2.40 ln(L) + 0.23 ln(L) 2 ) SP = 0.9 (1- 0.667e (-0.006W – Wmin) ) (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Bioenergetic component mainly paramertised with herring data!

33. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn % potential survivors concerning spawning location April July Growth concerning spawning location through 10 mm SL April July

34. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn 3D hydrodynamic model Grid distance 5 km 60 vertical levels 5 Min time steps Lagrangian transport module advection & diffusion Prey fields IBM sprat eggs & larvae 3-D transport, turbulence Eulerian velocities, temperatures, salinities, oxygen, turbulence, light 3D-location Observations from field sampling IBM development – Baltic Sea

35. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Temperature [°C] IBM development – Baltic Sea

36. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Temperature & ingested prey Fourth feeding day Increment width [µm] Ingested prey Temp. Norm. Incr. width [µm/°C] IBM development – Baltic Sea

37. 21-01-2008 HM for ICES at Baltic RAC pelagic WG meeting Tallinn Modelling juvenile distribution Mean modelled juvenile distribution 1979-2002; all areas Mean observed juvenilev distribution hydroacoustics