1. GS1 Multispecies models Issues and state of art in modelling Issues in interpretation and implementation Gunnar Stefansson Marine Research Institute/Univ. Iceland

2. GS2 Models Single species Statistics Biological interactions Technical interactions Spatial effect Temporal variation Economics

3. GS3 Models - single species Conclusion: Low F

4. GS4 Models - more Effect of reduced fishing on predator? Effect of increased harvest of prey? Effect of fishing in spawning area? Effect on bycatch species? Uncertainty in estimates? Predictive capability? Need statistical multispecies explicit spatial models

5. GS5 Models - statistics Natural variation Measurement errors Nontrivial effects of incorrect methods... Estimation of unknowns Prediction of effects with uncertainty Conclusion: Lower F

6. GS6 Models - biological interactions Predation Growth Maturation Migration Spawning Fishing mortality Natural mortality Processes to be included in holistic models Others: Hydrography, larval drift, spawning location, maternal effects,... Need to (1) predict (2) understand Data?

7. GS7 Models - technical interactions Species mix in catches Different mix in different gears Prediction of effects of gear regulation

8. GS8 Models - spatial effects Nursery areas and spawning areas Migration Spawning fishery Species overlap is spatially variable Spatial variation in growth Need to (1) predict (2) understand Data?

9. GS9 Models - economics Different species: Different prices Costs of effort by fleet

10. GS10 Models - temporal variation Single species, annual assessments Annual data and analyses Multispecies interactions and migrations: Finer temporal scales

11. GS11 Models - current status Greater uncertainty than earlier thought Multispecies concerns are important Statistical techniques essential Need holistic models for understanding

12. GS12 Precautionary approach Reference points –F or B for single species –F mainly for multispecies? Uncertainty –Increases with recent models –Requires lower F Multispecies reference points? Precautionary harvesting of prey species??

13. GS13 Biological interactions (growth) Is it in accordance with the PA to harvest the prey?

14. GS14 Control mechanisms Closed areas TAC Effort regulation Mesh sizes (fishing gear limitations)

15. GS15 Overcapacity Introduces problems in all control systems Reduces likelihood of efficiency in any control measure Increases political pressure and likelihood of deviations from earlier policy Needed: Models of these effects

16. GS16 Closed areas Virtue Guarenteed protection within the area Problems? Choice of size and location of area Effect of migration and fishing outside area Enforcement Major issue

17. GS17 Closed areas F E I F E I No (measurable) effect on mortality Likely effect on mortality but not economical 20%: Unlikely to workExtreme, 90%: Likely

18. GS18 Closed areas: Overcapacity What is the upper bound on fishing mortality outside the closed area? Historical low catch outside does not mean catches cannot be taken outside! Small closed area+overcapacity: No effect on F

19. GS19 TAC limitations Virtue Direct limitation of fishing for given species Problems? Uncertainty in estimating correct TAC Species mis-match Discards Enforcement F at 75% of F crash : UnlikelyExtreme F at 10% of F crash : Likely Major problem Major issue

20. GS20 TAC limitations: Overcapacity Dormant capacity (Latent effort) Can always catch quota if overestimated Will introduce discards when TAC underestimated (multispecies effect) Effect on bycatch species often unknown Get biassed effect (overshoot F on average) due to the system itself In toto: Major problems Need spatial and multispecies models for understanding

21. GS21 Effort regulation Virtue Direct limitation of all effect on the ecosystem Problems? Effort reallocation species/components Efficiency/catchability trends Only guaranteed to work if very low effort allowed Vessel classes? Enforcement? E at 80% of E current : UnlikelyExtreme: E at 40% of E current : Likely Major problem Major issue

22. GS22 Effort regulation: Overcapacity Effort and capacity: Very similar effects Overcapacity: Political pressures Exchange of effort-days to more efficient vessels Need spatial and multispecies models for understanding In toto: Major problems

23. GS23 Mesh sizes (gear limitations) Virtue Direct limitation of fishing for juveniles or... May make fishery sustainable Pacifier Problems? Slippage mortality? Often negligible effect Enforcement Major issue

24. GS24 Mesh sizes: Overcapacity Can often negate effect In general it is not clear that mesh changes or common gear regulations have any effect at all

25. GS25 Back to models: Model requirements Uncertainty: –Better statistical models Areal closures: –Spatial models Effort control, analysis: –Spatial models –Multispecies, technical interactions TAC control: –Multispecies, technical interactions Understanding any controls: –Need to estimate effect of major change in predator on prey abundance and vice versa –Multispecies, biological interactions

26. GS26 Effects of current model output Uncertainty output: –Need lower F Multispecies output: –Need lower F on prey Areal closures: Large areas (or more controls) Effort control:Lower effort+annual reductions+TAC TAC control: Lower TAC+effort/fleet reductions Almost all analyses: –Need lower F

27. GS27 Limitation summary TAC: Species allocation mismatch+uncertainty Closed area: Migration/fishing outside+uncertainty Effort control: Effort reallocation+catchability Fleet reduction alone: Like effort Common effects of levels of measures: 10% reductions: No effects 50% reduction: Some effect likely but can be negated 90% reductions: Almost sure effects but may lose catches

28. GS28 Source of problems Effort control: –Correct effort uncertain –Lacks species catch limits –Lacks annual reductions –Effort too close to target TAC: –Correct TAC uncertain –Fleet too large –Dormant effort –TAC too close to target Closed area: –Correct area uncertain –Fleet too large –Dormant effort –Area too small

29. GS29 Solutions? Extreme measures? or Combined systems? or ? No single system, set at its target will suffice in general!

30. GS30 Combinations TAC + Effort control! TAC + Closed area? Effort control + closed area ? + Fleet reduction!!

31. GS31 Current theme Marine resources can be harvested using the maximum fleet size economically possible up to that maximim level of fishing mortality which does not demonstrably lead to stock collapse.

32. GS32 A new tenet Marine resources should be harvested using the minimum fleet size possible and at that minimum level of fishing mortality which does not demonstrably lead to a serious long-term loss of catch.