This section includes parameters describing the management agency’s ability to implement an MP that institutes a catch limit (TAC). For example, an MP may specify a certain TAC, but the managing agency may be unable to stop fishing at the exact moment that the quota is obtained, resulting in quota underages or overages.
TACFrac and TACSD allow the user to specify the actual catches that are taken as a fraction of the desired TAC in the form of a distribution that allows variability between simulations and years.
TACFrac
Mean fraction of recommended TAC that is actually taken. For each historical simulation a single value is drawn from a uniform distribution specified by the upper and lower bounds provided. This value is the mean TAC fraction obtained across all years of that simulation, and a yearly TAC frac is drawn from a log-normal distribution with the simulation mean and a coefficient of variation specified by the value of TACSD drawn for that simulation. If the value drawn is greater than 1 the amount of catch taken is greater than that recommended by the TAC, and if it is less than 1 the amount of catch taken is less than that recommended by the TAC. Positive real numbers.
TACSD
Log-normal coefficient of variation in the fraction of recommended TAC that is actually taken. For each historical simulation a single value is drawn from a uniform distribution specified by the upper and lower bounds provided. This value is used, along with the TACFrac drawn for that simulation, to create a log-normal distribution that yearly values specifying the actual amount of catch taken are drawn from. Positive real numbers.
Custom Parameters
See Custom Imp Parameters for information on specifying simulation- and year-specific implementation error values.
Interactive App
Choose upper and lower bounds for TACFrac and TACSD. Based on these ranges, the parameter values for 5 simulations will show in the table. Click on any line of the table to view how those parameter values affect the implemented vs. desired TAC in a hypothetical catch limit MP.
- Figure 1 shows the effects of implementation error in the recommended TAC over 50 projection years in a single simulation. The red line shows the TAC recommended by the MP, while the blue line shows the actual effort limit applied by the model. The location of the blue line relative to the red line is influenced by whether
TACFracis greater or less than 1, and the variability of the blue line over time is influenced by the value ofTACSD, with larger values resulting in greater variation between years.