1 / 14

150 likes | 343 Vues

Age-structured models (continued). Fish 458, Lecture 5. Building Age-Structured Models. Age-structured models are constructed by selecting specific hypotheses for each key population dynamic process: Growth, fecundity, natural mortality, exploitation, recruitment

Télécharger la présentation
## Age-structured models (continued)

**An Image/Link below is provided (as is) to download presentation**
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Content is provided to you AS IS for your information and personal use only.
Download presentation by click this link.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

**Age-structured models(continued)**Fish 458, Lecture 5**Building Age-Structured Models**• Age-structured models are constructed by selecting specific hypotheses for each key population dynamic process: • Growth, fecundity, natural mortality, exploitation, recruitment • These process can be time-invariant, stochastic, density-dependent or depensatory. • They can be linked via forcing functions (e.g. environmental variability)**Typical outputs of an Age-structured Model (northern cod)**• Abundance of various age-classes (typically the offspring). • Trends in key population components: • Spawner biomass • Exploitable biomass • Trends in fishing mortality • Usually averaged over a number of age-classes.**Continuous Fishing - I**• Many models assume that fishing and natural mortality occur continuously throughout the year. For a single year class: • M is the instantaneous rate of natural mortality, and • F is the instantaneous rate of fishing mortality.**Continuous Fishing - II**• The catch from a cohort over a year is given by: • Note that assuming that fishing occurs continuously throughout the year is seldom very different from assuming that it occurs instantaneously in the middle of the year (the first-order Taylor series approximation).**Building an age-structured model-II**• Build a model of a harvested seal population. • The sex ratio at birth is 50:50. • The survival rate in the absence of harvest is the same for females and males younger than 12 (when they achieve harem bull status). • Pups and harem bulls are harvested. • The survival rate for pups is related to water temperature according to the equation:**The model (females)**Pup harvest and first-year survival 50% of pups are females Pups are females multiplied by the age- specific pregnancy rate Plus-group dynamics**The model (males)**Pup harvest and first-year survival 50% of pups are males Plus-group dynamics (bull catches; high M for harem bulls)**More Model Structure-I**• This seal model is based on the population of Cape fur seals off Namibia. How would you extend it to account for: • a harvest of females; • a split of the pup harvest between males and females which differs from 50:50; • a relationship between the survival rate of females and an environmental variable; and • density-dependence on pup survival or pregnancy rate.**More Model Structure-II**This model makes many assumptions - which ones do you consider to be the least realistic? Can you identify the state variables, forcing functions and parameters?

More Related