Leire Ibaibarriaga

Testing spatial heterogeneity with stock assessment models

This paper describes a methodology that combines meta-population theory and stock assessment models to gain insights about spatial heterogeneity of the meta-population in an operational time frame. The methodology was tested with stochastic simulations for different degrees of connectivity between sub-populations and applied to two case studies, North Sea cod (Gadus morua) and Northeast Atlantic sardine (Sardina pilchardus). Considering that the biological components of a population can be partitioned into discrete spatial units, we extended this idea into a property of additivity of sub-population abundances. If the additivity results hold true for putative sub-populations, then assessment results based on sub-populations will provide information to develop and monitor the implementation of finer scale/local management. The simulation study confirmed that when sub-populations are independent and not too heterogeneous with regards to productivity, the sum of stock assessment model estimates of sub-populations’ SSB is similar to the SSB estimates of the meta-population. It also showed that a strong diffusion process can be detected and that the stronger the connection between SSB and recruitment, the better the diffusion process will be detected. On the other hand it showed that weak to moderate diffusion processes are not easy to identify and large differences between sub-populations productivities may be confounded with weak diffusion processes. The application to North Sea cod and Atlantic sardine exemplified how much insight can be gained. In both cases the results obtained were sufficiently robust to support the regional analysis.

Uncertainty estimation and model selection in stock assessment models with non-parametric effects on fishing mortality

Uncertainty estimation and model selection in stock assessment models with non-parametric effects on fishing mortality Leire Citores*, Leire Ibaibarriaga, and Ernesto Jardim AZTI-Tecnalia, Marine Research Unit, Txatxarramendi Ugartea z/g, 48395 Sukarrieta, Basque Country, Spain BCAM Basque Center for Applied Mathematics, Applied Statistics, Mazarredo 14, E48009 Bilbao, Basque Country, Spain Sustainable Resources Directorate, Water and Marine Resources Unit, European Commission Joint Research Center (JRC), Via Enrico Fermi 2749, 21027 Ispra (VA), Italy *Corresponding author: tel: þ34 667 174 393; fax: þ34 946 572 555; e-mail: lcitores@azti.es