Slide 1

Sigurd Tjelmeland Barents Sea multispecies harvesting control rules in the making (well, thought-of, anyway) IMR workshop 13-15 september 2004 A practical approach focusing on Barents Sea capelin and on the use of biological models Slide 2 Multispecies harvesting control rules?? Interest in single-species HCRs just awakened Why multispecies? No less will be accepted in the Barents Sea (orchestra, but chamber rather than symphonic)! Last couple of decades lots of pressure from fishers Simple ecosystem public concern concentrates on cod- capelin-herring-harp seal dynamics This is also the scientific issue in focus Slide 3 Which model? Multispecies models used in assessment Bifrost Cod-capelin, harp seal soon Herring influence on capelin recruitment through recruitment function SeaStar Consumption of herring by minke whales Other existing multispecies models Gadget ScenarioC Systmod MSVPA New multispecies model? Slide 4 Principal food web in the Barents Sea Slide 5 Consumption by cod Slide 6 Multispecies HCRs in the Barents Sea two directions Assessment direction The underlying model is used in the yearly assessment Management approach Russian-Norwegian Commission What is the expected level of yield can evolve into HCRs Step 1: Putting together what we have got Step 2: Use of multispecies models Slide 7 Focal point in the Barents Sea: Capelin Capelin is the most important food item for cod A HCR for the Barents Sea must incorporate the long-term effects on capelin from the cod and the capelin (and the herring?) fishery The spawning stock recruitment relation for capelin must be known We cannot measure the capelin spawning stock So it all starts by modelling the capelin spawning stock Slide 8 Focal point in the Barents Sea: Capelin Slide 9 HCR for Barents Sea capelin (absolute stock measurements) Before 1983-1986 collapse Spawning stock 0.5 million tonnes Based on simulations Target reference point Now 5% probability of spawning stock below 0.2 million tonnes, predation by cod taken into account Basis: 1989 spawning stock Limit reference point Ad hoc HCRs suggestion from scientists, followed by managers on a year to year basis Slide 10 The Bifrost model Stochasticity throughout Input Replicate files of September estimates Replicate files of consumption per cod Replicate files of (VPA) herring (from SeaStar) Historic parameters generated Replicate values of maturation parameters Replicate values of predation by cod parameters Replicate values of historic M on immature capelin Replicate values of recruitment relation parameters Slide 11 The basis for management of capelin Slide 12 Possible basis for HCR for capelin: Optimal spawning stock Possible definitions of optimality: Maximising expected long-term yield Maximising expected long-term revenue Investigating (possible) machinery for evaluating HCRs for capelin Ancient: Target reference point with consideration of M-output biomass (Hamre) (1982 - the start) Slide 13 Evaluation of HCRs for capelin conditional on cod (constant at present) and herring (different scenarios) stocks Computational scheme 1Fix stochastic events 2Set value of target spawning stock 3Perform long-term simulation, taking catch above target spawning stock, if possible 4Change value of target spawning stock, repeat 3 5Repeat 2-4 until optimal target spawning stock has been found 6Repeat 1-5 several times and get distribution of optimal target spawning stocks 7Repeat 1-6 for different levels of herring and (possibly) cod in the Barents Sea Slide 14 Target spawning stock for capelin for different sizes of the herring stock Slide 15 Multispecies HCRs for the Barents Sea: A long way to go Year-round consumption of capelin by cod in Bifrost Dynamic cod Inclusion of consumption of capelin by harp seal Females in the spawning period Year-round feeding by the total stock Other species Weighting yield from different species Slide 16 Multispecies HCRs for the Barents Sea: Focal problems Short term Harp seal migration data and diet data Communication with management Long term Diet of humpbacks (and other large whales) Slide 17 EKSEMPEL P OVERSKRIFT Eksempel p tekst Bruk gjerne fonten Arial (fet) ved bruk av variant mrkebl bunn