Effects of interactions between fish populations on ecosystem dynamics and fish recruitment in the Norwegian Sea

Transkript

1 Effects of interactions between fish populations on ecosystem dynamics and fish recruitment in the Norwegian Sea Kjell Rong Utne and Geir Huse Nordic Climate-Fish 16. August

2 The great depths in the Norwegian Sea provides ideal conditions for overwintering zooplankton The area is an important feeding area for planktivorous fish like NSS herring, blue whiting and mackerel Barents Sea Norwegian Sea North Sea

3 25 Biomas of pelagic fish in the Norwegian Sea Herring SSB Mackerel TSB Blue whiting TSB Total biomass Biomass (million tons) Year After the herring collapse in the 60ies it was discovered large concentrations of blue whiting in the Norwegian Sea This lead to speculations about interactions between the fish stocks

4 Time periode: The Inferno project Collaboration between scientists from Norway, Iceland, Faroe Islands and Russia, lead by IMR Primary data sources were acoustic data and research trawl catches Resulted in 10 papers focusing on interactions between pelagic fish and interactions between fish and zooplankton

5 Two papers explicit on the spatial distribution of fish Overview of the migration and the changes in these patterns Overview of the spatial overlap between the species Indications of possible competition

6 Blue whiting in May 1996 og 2001 Ambient temperature 5.3 C Stock size 3.5 mill tonnes Ambient temperature 5.3 C Stock size 9.5 mill tonnes

7 Overlap between the species, July-August

8 Vertical distribution of herring and blue whiting, day/night Herring - day Herring - night Blue wh - day Blue wh - night Upper kvartile Lower kvartile

9 Understanding ecosystem processes Limitations with surveys observations These observations are snapshots of the reality There are large changes in space and time It is difficult to fully understand what s going on a long time scale We can not fully understand the dynamics with observations only Ecosystem models can help us understand dynamics on a large scale

10 Modeling fish migration Objective: Recreate annual migrations patterns with a focus on the feeding period Quantify horizontal overlap between the species during the feeding periode with daily resolution

11 Methode: Individual based model of fish migrations Genetic algorithm to optimize migration parameters Calibration with survey observations (early and late in the summer) Herring and blue whiting echo sounder Mackerel trawl catches

12 Migration model Individual movement Directive Stochastic Advection The fish cannot migrate into water masses colder than 2 (her and bw) or 8 C (mac).

13 Svalbard Greenland Sea Iceland Jan Mayen Norwegian Sea Iceland Sea Hardwired movement Blue whiting Mackerel Herring North Sea Norway Optimised movement Blue whiting Mackerel Herring

14 Predictions May Observations Predictions July/Aug Observations Mackerel Herring Blue whiting

15 Herring migration vectors Black arrows Early summer Gray arrows Late summer

16 Overlap between two species Overlap between three species

17 Flowdiagram for the coupled model } Hjøllo et al, MBR 2012

18 Feeding behaviour fish Bioenergetics model with parameters optimized for each species Holling type 2 functional response Feeding level CF (g/m 2 )

19 Feeding behaviour fish Bioenergetics model with parameters optimized for each species Holling type 2 functional response Feeding level Other prey Migration Calanus Slow Random walk CF (g/m 2 )

20 Total consumption in 1997 All numbers in million tonnes C finmarchicus Other prey Herring Blue whiting 4 14 Mackerel Totally Annual Calanus production is unknown Rough estimate is 300 million tonnes (Skjoldal et al 2004)

21 Effect of spatial resolved feeding by fish on C. finmarchicus August June The difference between dynamic and uniform predation

22 Summary modelling -Implemented pelagic fish in the Norwecom model system Improved fish migrations Improved predation pressure on C. finmarchicus - The total consumption of zooplankton by pelagic fish is slightly higher than previous estimates

23 Length for herring, mackerel and blue whiting (age 6) Reduced length at age for herring and mackerel Reduced length at age for blue whiting, but reversed in 2008 together with a very low stock size of blue whiting

24 Planktonproduction and fishconsum Reduced zooplanktonproduction and increased predation by fish since 2003 Mackerel Blue Whiting Herring Zoo. index Calanus con./prod. ratio Biomass of pelagic fish (mill. tonnes) Zooplankton index Year Consumption/production ratio

25 Thank you

26 I løpet av studieperioden har vi sett: Sterk oppbygging av biomasse av planktonspisende fisk i Norskehavet Reduksjon i dyreplankton mengde Endringer i romlig fordeling av fisk Økt konsum/produksjon ratio for dyreplankton Redusert fiskevekst tetthetsavhengig for alle og interspesifikk for sild og kolmule Konklusjoner Resultatene indikerer at biomassen av planktonspisende fisk i området har vært over bæreevnen og støtter dermed hypotesen om at de planktivore fiskebestandene konkurrerer om føden Viderefører arbeidet med utvikling av flerbestandsmodell for Norskehavsbestandene og til årets assessment av raudåte

27 Test av interaksjoner mellom sild, kolmule og makrell All bestandene viste tetthetsavhengig størrelse ved alder (6) For sild og kolmule var der også signifikante effekter av interspesifikk konkurranse ( ) Herring Mackerel Blue whiting Intraspecific biomass 5.36E Interspecific biomass Total biomass 4.96E

28 Mare Cognitum I 1997 Mare Cognitum II 1998 INFERNO 2012

29 Horisontal overlapp mellom bestandene

30 Artsforskjeller i beitekapasitet Konsum (g/g fisk) Calanus finmarchicus (g/m 2 )

31 Romlig utbredelse av fisk i løpet av beitesesongen -97 Mai Juni Juli August