WP 2: Impact of exogenous processes on recruitment dynamics

Description of tasks

Task 2.1: Identification of Critical Life stages and Processes

Work to be conducted will include development of new proxy indices based on process knowledge developed in this project (e. g., WP1, WP2.2 & 2.3, WP3) and statistical analyses of time series of recruitment, egg production and environmental variables/proxies. The task will identify critical periods and life stages in the recruitment process for species and stocks considered and identify time periods of high and low recruitment and probable causes for these variations.

Task 2.2: Develop Process Understanding and Models

This task will use results from field and experimental studies conducted in previous and ongoing EU and national projects (e.g., STORE, STEREO, LIFECO, contributions to the international GLOBEC programme) to investigate factors affecting production, distribution and survival of eggs, larvae and early juveniles. Knowledge derived from (re-)analysis of past and ongoing process studies (e.g., egg and larval spatial and temporal distributions, archived larval otoliths) will assist to distinguishing between key drivers and the development of new proxy variables for recruitment modelling. .

Task 2.3: Implement Process Knowledge in Biological-Physical Individual-based Oceanographic models

Recruitment ultimately depends on individual eggs, larvae and juveniles successfully surviving a series of events, interactions and processes. This task will incorporate process knowledge in coupled bio-physical individual-based models (IBMs) which allow the fate of individual fish eggs and larvae to be modelled as they develop and grow along their drift routes in the field. The task requires development and integration of process models (e.g., feeding, distribution) across both small (e.g., cm-m in the vertical) and intermediate (1-10 km) scales so they can be incorporated into the kilometre scale resolution used in particle tracking models. The IBM approach, when combined with field data (e.g., abundances and spatial distributions of juveniles, otolith growth and hatch-date information, biochemical indices of condition from Task 2.2) is a powerful tool for identifying how environmental processes affect recruitment and for developing new proxy variables of environmental variables which can be used in statistical analyses of inter-annual recruitment variability (Task 2.1).

Task 2.4: Scenario Modelling Variations in Biological and Physical Forcing to Develop Predictive Capacities with Respect to Stock Recovery

The IBMs developed in 2.3 will be used in exploratory fashion to evaluate the roles of realistic changes in egg production (e.g, via changes in spawner biomass and size/age composition) and environmental variability (e. g., historical and expected future climate changes) on recruitment. Recruitment success can then be compared with that expected under equilibrium and randomly varying environments to quantify the magnitude of recruitment uncertainty associated with environmental forcing, and hence the basis for potential stock recovery.

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