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Approaches to Sustainable Yields: Surplus Production, Yield-per-Recruit, and Population Mo, Slides of Biology

Institute of Company Secretaries of IndiaBiology

An overview of different approaches to determining sustainable yields for various species, focusing on surplus production models and yield-per-recruit models. Surplus production models estimate the dome-shaped yield curve based on historical data, while yield-per-recruit models maximize yield under the tradeoff between numbers and value. The document also mentions population modeling for species with sufficient data.

Typology: Slides

2012/2013

Uploaded on 01/26/2013

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sambandan 🇮🇳

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Comparison of Approaches to
Sustainable Yields
•There are many approaches to
determining what approach should be
established for sustainable yields
•Various strengths and weaknesses
(think of a demographic model with all
the parameters)
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Download Approaches to Sustainable Yields: Surplus Production, Yield-per-Recruit, and Population Mo and more Slides Biology in PDF only on Docsity!

Sustainable Yields

  • There are many approaches to determining what approach should be established for sustainable yields
  • Various strengths and weaknesses (think of a demographic model with all the parameters)

Sustainable Yields

  • Surplus Production models are also called surplus yield models or “production” models
  • Frequently used in fisheries
  • If you know how yields have responded to different levels of exploitation effort over time, then you could estimate the dome-shaped yield curve (thus not requiring new data)

Sustainable Yields

  • There are many pitfalls with this approach including it treats all years as replicates - Consider Cod
  • The largest fisheries collapse ever (Peruvian anchovy) in the early 1970’s when it adopted a surplus production model that suggested levels were safe

Sustainable Yields

  • Yield-per-recruit models were developed originally as part of the “dynamic pool” concept in the landmark fisheries book written by Beverton and Hold (1957)
  • The dynamic pool attempts to keep track of separate processes that add to a population (e.g. recruitment and growth) or subtract from it (e.g. natural and catch mortality)

Sustainable Yields

  • Once the level of mortality has been found that maximizes the yield per recruit, we can calculate the total yield that will be obtained from a given level of mortality, if we know how many recruits are coming each year
  • This approach is used in many countries
  • Does require info about how the value (often size) of individuals increases with age, as well as an estimate of natural mortality rates

Sustainable Yields

  • For some species ($ or conservation) there is enough data for full-blown population models
  • These models combine data on all demographic parameters (survival, age at maturity, age-specific mortality)

Sustainable Yields

  • Projected annual strandings for Kemp’s ridley seas turtles under levels of compliance by shrimpers (current to full compliance)

Sustainable Yields

  • Adjustments based on recent results
  • If we can monitor either the population itself or the numbers of individuals taken, we can adjust the quotas each yr based upon new information
  • This is currently the approach for waterfowl and mammal hunting in the US (read Box 8.1 on martens)

Sustainable Yields

  • Of course there are many potential problems with this simplistic model
  • There are problems with cull rates compared to mortality rates…why?
  • Are density estimates accurate? Why?
  • Estimating λmax is not easy and variable

Sustainable Yields

  • There are spatial and temporal problems of establishing accurate production numbers