Sensitivity of a Multisystem Length Limit Model

Length limits are among the more visible and impactful functions of management paradigms.  While agencies often implement standard length limits for species occupying multiple systems, evaluating these regulations typically occurs on individual water bodies.  Few studies have explored the possibility of developing a method for evaluating regional harvest limits.  A consistent framework for evaluating multiple-system length limits can add valuable guidance and assurance towards exploring alternative regulations.  Our objectives are to build a model that assesses length limits over multiple waterbodies with an extension of the Beverton-Holt yield-per-recruit (YPR) function, and evaluate the sensitivity of inputs on the multisystem YPR function.  This YPR function simulates predicted yield for cohorts from multiple systems by including a catch-at-age and weight-at-age function for each system’s cohort.  An analysis of the model sensitivity indicates that changes in fishing and natural mortality have a greater impact on the model outcome, while the inputs of the weight-at-age function play a much smaller role.  However, high mortality rates can elevate the importance of weight-at-age inputs towards the model, and in cases of high exploitation (F>0.5), weight-at-age parameters can play a significant role in affecting risks of growth overfishing for a given length limit.