The Lagrangian Ensemble Recruitment Model (LERM)
A new individual based ecosystem model for predicting fisheries recruitment
Matteo Sinerchia and John Woods Imperial College London (UK) PROBLEM 1. The methods available for modeling and management of fishing on cephalopods were mainly adapted from those used for fin fish and most of them involve assumptions that are not completely appropriate to cephalopods (Boyle and Rodhouse, 2005). Squid are short-lived, fast-growing and semelparous. The exploited stocks are particularly dependent on recruitment, which is variable and sensitive to changes in environmental conditions. 2. One of the main factors afftecting recruitment is the abundance of plankton at hatching (Hjort, 1914; Cushing, 1975; Agnew et al., 2000; Boyle and Rodhouse, 2005). At the moment there is no model to predict squid recruitment as a function of the variability of the food induced by environmental changes. SCIENTIFIC CHALLENGE 1. Create a new ecosystem model, inspired by the Reykjavik Declaration (FAO, 2002) in which also the food for the squid (zooplankton) is modelled explicitly. 2. Model the physiological response of individuals to environmental changes. METHOD LERM (Sinerchia et al., 2008) is a new 1D ecosystem model based on phaenotypic rules for physiology and behaviour derived from laboratory experiments for all species and it is integrated using the Lagrangian Ensemble metamodel (Woods, 2005), which treats plankton as individuals. Sensitivity of recruitment to changes in 1) nutrients, 2) abundance of competititors on, 3) abundance of visual predators, 4) number of squid eggs laid annually, 5) timing of squid spawning. The Lagrangian Ensemble metamodel
Agent-based modeling
population
integration of all individuals bio-feedback
LERM
I
E
Agent represents an individual plankter and carries information about a dynamic sub-population. Emergent Demography and Bio-feedback are computed by summing over sub-populations.

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