Modelling salmon and habitat What is a model

Modelling salmon and habitat

What is a model • A simplified abstraction of a more complex object • A model airplane - has some of the characteristics - Boeing used to build physical models of airplanes and wings • Now they build computer models • An architects model

Why models for salmon recovery • We may have several options for habitat – Improve spawning area – Improve rearing area – Improve estuary • The effectiveness will depend on where the limits are for the stock in question

Need an accounting system • To understand how changing habitat at one life history stage affect total returns

Modelling terms • • • State variables parameters forcing functions rules of change the state variables in the future depend upon the current state, the parameters (constants), any external perturbations (the forcing functions), and the rules of change

State variables • The complete description of the current state of the system -- complete enough that you can “rebuild” the system with this amount of information • examples – the number of fish in a river, the amount of large woody debris in a section of stream, the maximum winter flow ….

Parameters • Do not change over time and are the constants that describe the rates or limits • Examples – eggs per female at each age, fry to smolt survival when rearing habitat is not limiting, concentration of fine sediments above which egg survival starts to drop

Forcing functions • Natural or anthropogenic factors that affect the state • weather impacts on survival or reproduction • harvesting • These are “external” to the model -- that is we don’t attempt to describe the dynamics of these factors

Rules of change • The equations that describe how the state variables change over time in relation to the current values of the state, the parameters, the forcing functions. • St+1 = f(St, p, ut)

Components of rules of change • Logical relationships – statements that are true by definition – Fry = eggs * egg to fry survival – also known as tautologies • Functional relationships – specify the relationship between a rate and a state variable or something related to a state variable (egg survival as a function of fine sediments)

Deterministic or stochastic • Do we allow for random events, or not

Basic life stage model • Survival from one stage to the next depends on • Carrying capacity for that stage • “productivity” that is survival when capacity is not limiting

Habitat impacts • Productivity and capacity • For example egg to fry survival depends on fine sediments

Spawners to Egg • capacity depends on gravel area • productivity depends on age specific fecundity and age distribution of spawners

Eggs to Fry • capacity is unlimited • productivity depends upon % fines

Fry to Smolt • capacity determined by rearing area • productivity determined by % impervious

This approach is used • In the EDT approach of Mobrand et al • In work currently underway with Muckelshoot Tribe

The role of models in this seminar • To serve as a focus for discussion for individual speakers • To provide key questions for speakers • To determine what an analytic framework should do for planners • To move towards a PRISM salmon model