Sigurd Tjelmeland Barents Sea multispecies harvesting control rules in the making (well, thought-of, anyway) IMR workshop september 2004 A practical approach focusing on Barents Sea capelin and on the use of biological models

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

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?

Principal food web in the Barents Sea

Consumption by cod

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

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

Focal point in the Barents Sea: Capelin

HCR for Barents Sea capelin (absolute stock measurements) Before 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

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

The basis for management of capelin

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) ( the start)

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

Target spawning stock for capelin for different sizes of the herring stock

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

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)

EKSEMPEL PÅ OVERSKRIFT Eksempel på tekst Bruk gjerne fonten Arial (fet) ved bruk av variant mørkeblå bunn