Integrated, age-structured, length-based stock assessment model with uncertain process variances, structural uncertainty, and environmental covariates: case of Central Baltic herring

Abstract

We developed a generic, age-structured, state-space stock assessment model that can be used as a platform for including information elicited from stakeholders. The model tracks the mean size-at-age and then uses it to explain rates of natural and fishing mortality. The fishery selectivity is divided to two components, which makes it possible to model the active seeking of the fleet for certain sizes of fish, as well as the selectivity of the gear itself. The model can account for uncertainties that are not currently accounted for in state-of-the-art models for integrated assessments: (i) The form of the stock–recruitment function is considered uncertain and is accounted for by using Bayesian model averaging. (ii) In addition to recruitment variation, process variation in natural mortality, growth parameters, and fishing mortality can also be treated as uncertain parameters. The use of the model is exemplified in the context of participatory modelling where stakeholders have specified how environmental variables affect the stock dynamics of Central Baltic herring (Clupea harengus membras).