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YPR Model

Line Art Drawing of a Fish

Yield per Recruit


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Version 3.3 (September 2013)

Core Application


Yield per Recruit (YPR) is a major revision of earlier implementations of the basic Thompson-Bell model for estimating the expected lifetime yield and biomass from a cohort subjected to varying levels of fishing mortality.

The present version estimates life-history parameters such as mean age, mean generation time, and expected number of spawnings.  In addition the user can investigate the resulting age composition of catch and abundance under different levels of fishing mortality.

The latest version of YPR allows the user to incorporate uncertainty in weights at age, natural mortality, maturity, and fishery selectivity.

The user can optionally enter the coefficients of either a Beverton-Holt or Ricker stock recruitment relationship and perform a Sissenwine-Shepherd analysis for equilibrium estimates of maximum sustainable yield (MSY) reference points (FMSY and BMSY).

The user can also conduct sensitivity analyses for any model parameter. Data visualization methods are emphasized to allow exploration of the population consequences of changes in fishing mortality.


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Gabriel, W.L., M. P. Sissenwine, and W. J. Overholtz. 1989. Analysis of spawning stock biomass per recruit: An example of Georges Bank haddock. North American Journal of Fisheries Management 9:383-391, 1989.


Thompson, W.F. and F.H Bell. 1934. Biological statistics of the Pacific halibut fishery. (2) Effects of changes in intensity upon total yield and yield per unit of gear. International Fisheries Commission Report, No. 8, 1934.


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Version History


YPR Version 3.3 (September 2013)

  • Added ability to include uncertainty to vectors which have traditionally been assumed constant: weights at age, natural mortality, maturity, and fishery selectivity. Sensitivity analysis modified to allow wider range of conditions to be explored.

YPR Version 2.7.1 (May 2007)

  • Fixed a bug where selecting Create a New Case from the File menu caused the GUI to crash.


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Older Version Changes 


YPR  Version 2.7 (April 2007)

  • Includes a new grid editing tool with easier data entry and copy/paste abilities. 

  • Ability to save files with spaces in the file name, and use spaces in folder names.

  • Upgraded version of the plotting package.


YPR Version 2.6.2 (May 2006)

  • Fixed minor graphics bug which constrained the values that could be entered for recruitment equation coefficients.  All constraints have been dropped


May 2003

  • The age based YPR graphical interface was completely rewritten for this version.  In addition to the new style features the plot displays have been improved.

  • User may specify three weight vectors: Catch Weight, Stock Weight, and Spawning Stock Weight. This may be of value for fast growing species.

  • The model now allows a user to input parameters for Stock Recruitment equations and perform a Sissenwine-Shepherd analysis.


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NOAA Fisheries Toolbox Version 3.1

website last modified May 16, 2016


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