Approximating openMSE to Grym

Introduction

[background on GRYM]

[background on openMSE]

• Main goal

  • Demonstrate that the {openMSE} framework, along with its primary package {DLMTool}, is a suitable and effective tool for conducting management strategy evaluation analysis for the Antarctic Krill stock.

Analysis outline

• We use the powerful and highly customisable features of the {DLMTool} package to approximate the methodological approach currently used for the management of the krill fishery, which is based on the Generalised Yield Model (GYM) and implemented in {GRYM} package.

• (…)

Simulation scenarios

• We compare results from population simulations conducted under each framework for 8 alternative sets of model inputs. These entail combinations of four different sets of Proportional Recruitment estimates and 2 sets of maturity at age estimates.

  • why 4 PR scenarios? R and M are the two key sources of uncertainty modelled in GRYM (confirm this). Maschette et al showed that the choice of PR scenarios had the greatest impact on the estimated gammas.

  • why 2 sets of size at maturity scenarios? Differences in maturity at age/length affects the fraction of spawners in the population that are vulnerable to the fishery. Under equal fishing selectivity, higher proportion of matures at lower sizes imply faster decline in SSB in relation to SSB0, which will result in different estimates of gammas.

Constable, A, and W. de la Mare. 1996. “A Generalised Model for Evaluating Yield and the Long-Term Status of Fish Stocks Under Conditions of Uncertainty.” CCAMLR Science 3: 31–54.

Kawaguchi, So. 2016. “Reproduction and Larval Development in Antarctic Krill (Euphausia Superba).” In Biology and Ecology of Antarctic Krill, edited by Volker Siegel, 225–46. Advances in Polar Ecology. Cham: Springer International Publishing. https://doi.org/10.1007/978-3-319-29279-3_6.

Maschette, D, S Wotherspoon, S Kawaguchi, and Philippe Ziegler. 2021. “Grym Assessment for Subarea 48.1 Euphausia Superba Populations.” WG-FSA-2021/39. Hobart, Autralia: CCAMLR. https://meetings.ccamlr.org/en/wg-fsa-2021/39.

SC-CAMLR. 2000. “Report of the Bo Workshop.” SC-CAMLR-XIX. Annex 4, Appendix G. CCAMLR.

Thanassekos, S, K Reid, S Kawaguchi, S Wotherspoon, D Maschette, P Ziegler, D Welsford, et al. 2021. “Grym Parameter Values for Subareas 48.1, 48.2 and 48.3.” WG-SAM-2021/12. CCAMLR.