Depletion-Corrected Average Catch (DCAC)

Depletion-Corrected Average Catch (DCAC) uses historical catch data and an estimated natural mortality rate to determine potential sustainable yield. An extension of potential-yield models, DCAC is based on the theory that average catch is sustainable if stock abundance has not changed substantially. The method differs from simple extrapolation of average catch to estimate sustainable yield by correcting for the initial depletion in fish abundance typical of many fisheries. DCAC divides the target stock into two categories: a sustainable yield component and an unsustainable “windfall” component, which is based upon a one-time drop in stock abundance for a newly established fishery. DCAC calculates a sustainable fishery yield, provided the stock is kept at historical abundance levels.

Software for conducting DCAC can be downloaded free of charge from the NOAA Fisheries Toolbox website at https://nmfs-fish-tools.github.io/. 

Inputs:

• Common Life History Parameters
• Historical catch data (preferably ten years or more), including average catch and any approximate relative changes in stock size during the period the catch was taken
• Estimated initial catch or unfished biomass
• Natural mortality rate (M) (preferably .02 or smaller, making this method more suitable for long-lived fish than for short-lived fish)
• Ratio of the fishing rate at Maximum Sustainable Yield (FMSY) to the natural mortality rate (M) (F_MSY/M)

Outputs:

• Sustainable Yield* (based on average catch).

*Not to be used for setting overfishing limits (OFLs) because it does not account for low stock size.

Input Sensitivities, Assumptions and Caveats:

• Performs poorly with low starting abundance levels and should be used with caution for targets that are in rebuilding programs
• Assumes life history data are accurate
• Assumes change in stock status over time is known
• Assumes average catch has been sustainable if abundance has not changed
• Assumes catch is composed of both Sustainable catch and "Windfall" (unsustainable) catch. Model adjusts average catch to account for the Windfall
• Assumes summing the catch over the time series (years of available data) represents relationships of F_MSY/M and B_MSY/B₀

Reference points:

• stock status-based reference point to estimate sustainable yield, as a reference value to control F.
• F_MSY /M
• B_MSY /B_o

Recommendations:

Fishing mortality is adjusted through harvest control methods (e.g. catch limits, seasons, or spatial closures) based on how far apart these values are from TRP & LRP for OFL.