# Presentation: 050221

## GADGET - Globally applicable Area Disaggregated General Ecosystem Toolbox, www.hafro.is/gadget

- Bjarte Bogstad, Institute of Marine Research,
-  Bergen, Norway
- bjarte@imr.no

## History & relation to other models

- Models for boreal systems:
- MULTSPEC (IMR, Norway, 1980s-1990s)
- BORMICON (MRI, Iceland, 1990s) – New code
- Gadget (ca. 2000 and onwards)- Extension of BORMICON code
- Essentially same concept
- Gadget may be thought of as an extension of Stock synthesis method (Methot)

## Gadget

- Forward simulation model
- Create a virtual population within the model
- Follow the fish through their lives
- Fishing, mortality, growth, maturation, etc.
- Process driven
- E.g. percentage becoming mature, not percentage mature at age

## Gadget

- Age&length based
- State variables:  Number of fish and mean weight by age and length group
- Multiple: species, stocks, fleets, areas
- May divide a stock in e.g. mature/immature, female/male, each with different population dynamics
- Coarse resolution in time and space (month/quarter/yearly time step, few areas)
- Separation of model and data
- No data required for the simulation run

## Applications of Gadget

- Used both as a research tool and for practical stock assessment
- Single and multispecies models, as well as single-species and mixed fisheries
- Used both for fish, marine mammal and shellfish stocks
- Barents Sea, Iceland, Celtic Sea, Bay of Biscay, Mozambique

## Publications

- Stefansson and Palsson 1998- why are Gadget-type models suitable for boreal systems?
- Stefansson et al. – Statistical issues in such models
- Bjørnsson and Sigurdsson 2003 – Redfish application - Iceland
- Lindstrøm et al. Submitted – Whale-cod herring-capelin model – Barents Sea
- EU project reports – dst2 (2004), BECAUSE (2007)

## Slide 7

## Fitting model to data

- Statistical functions used to compare model and data - assign a numerical score to each data set
- Combined in a weighted sum to give a single likelihood score
- Repeat runs are made using different values of key parameters
- Optimisation algorithm used to find best fit of model to data
- Typically ~ 100 parameters in many Gadget models

## Area division - example

## Which data may be used in Gadget?

- Scientific survey data
- Commercial catch data
- Stomach content data
- Mark/recapture data
- Data and model resolution may be different

## Software

- Written in C++
- Can be run under UNIX/Linux and PC (using cygwin)
- Source code has to be downloaded, and then compiled on local computer
- Code has been used for many years – well tested
- Documentation and examples available on-line
- Graphics not included in package – only numerical output
- Further development of code not decided at the moment – main programmers have got new jobs

## Strengths

- Flexible tool
- May integrate a wide variety of information on different resolution (biological/spatial/temporal)
- Model and data independent
- Well documented
- Suitable for modelling systems with a few main species/interactions (e.g. boreal ecosystems)
- Age data not needed
- Gaps in data/knowledge may be identified – no hidden assumptions

## Weaknesses

- Some threshold to get started
- Computer-intensive
- Not the right tool if you have no data on length distributions

## ICES Multispecies WG in October

- The **Study Group on Multispecies Assessments in the North Sea** [SGMSNS] will be renamed the **Working Group on Multispecies Assessment Methods **[WGSAM] (Co-Chairs: John Pinnegar, UK and Bjarte Bogstad, Norway) and will meet at AZTI, **San Sebastian, Spain from 15–19 October 2007 **to:
- examine the status of multispecies modelling efforts throughout the ICES region, i.e. Bay of Biscay, Mediterranean Sea, Iceland, Barents Sea, Baltic Sea, North Sea (based on results from EU-funded BECAUSE), and consider the feasibility of using the various methods across regions;
- evaluate region-specific stomach sampling survey designs and preparation of guidelines and operation manuals;
- investigate the potential implications of a decline in forage fish for dependent wildlife, and the implications for prey stocks of recovering fish predator populations;
- investigate the relation between weight at age in the predator species and the abundance of prey species;
- compare forward projections from ecosystem models such as Ecopath with Ecosim (EwE) and multispecies assessment models.