ALADYM: an age and length-based single species simulator for exploring alternative management strategies

Abstract

-ALADYM (age-length based dynamic model) is an age-length based simulation model designed to predict the consequences of management scenarios on a single population, in terms of different metrics and indicators. Removals are simulated as total mortality modulated using a selectivity pattern and a fishing activity coefficient. ALADYM uses the classical equations of population dynamics to create a tool that uses fishery-independent information (e.g. from trawl surveys) as the primary source. The formulation of population dynamics at a small time scale (month) allows to model the effects of harvest controls that evolve through the year, which is particularly useful for fast growing species. The possibility of specifying a vector of natural mortality by age/length makes the model more suitable for situations where stocks are exploited at an early life stage, as in many Mediterranean fisheries, while introducing variations along the time of the harvesting pattern accounts for non-equilibrium situations. Stochastic effects can be added to some key life-history traits to incorporate uncertainty in input parameters and in their relationships. ALADYM can be used for a range of applications such as comparing management strategies, evaluating indicator changes or searching for reference points.

A user-friendly tool to assess management plans for European eel fishery and conservation

“…On the other hand, general-purpose software packages (e.g. those developed by Pauly et al, 2000;Kell et al, 2007;Lembo et al, 2009) are not structured to grasp the complexity of eel demography nor to guide users to properly define the functions describing the relevant processes and set up model parameters accordingly.…”

A Holistic Approach to Fishery Management: Evidence and Insights from a Central Mediterranean Case Study (Western Ionian Sea)

“…The BEMTOOL platform incorporates six operational modules, as follows: Biological, Pressure (the core model is ALADYM; Lembo et al, 2009), Economic, Behavioral, Policy/Harvest Rules, and Multi Criteria Decision Analysis (MCDA). BEMTOOL follows a multi-fleet approach and simulates the effects of several management trajectories on stocks and fisheries on a fine time scale (month).…”

Using the ALADYM simulation model for exploring the effects of management scenarios on fish population metrics

“…Over the time of the simulation, summer fishing activity was kept lower (∼0.44) than for the rest of the year to account for the seasonal fishing ban of trawlers in June-September. An alternative sub-model for selectivity was used (product of ogives sub-model selection parameter D 50% ; Lembo et al 2009) to simulate a harvesting pattern accounting for vulnerability/accessibility of the fish to the fishing gear. This was based on the knowledge about the fishing grounds targeted by differently equipped fishing units and the distribution of adult European hake in this area, where this species inhabits the deeper waters (Anonymous 2006).…”

“…In this study we applied the ALADYM (age-length based dynamic model) simulation model (Lembo et al 2009), a tool that does not requiring fishery-dependent data, and that operates on a monthly time scale mimicking the population at sea by the generation of numbers at age from a stock recruitment relationship or, alternatively, from a recruitment vector. This model is particularly useful to explore changes resulting from management measures, such as variations in size at first capture or fishing activity in situations such as the Mediterranean, where fish populations are generally exploited from a young age (e.g.…”

“…Further details regarding model specifications, basic assumptions, equations, advantages and limitations can be found in Lembo et al (2009).…”