catch means discard+landing, in this case can we use data of landing to estimate MSY
In general, discards are not of the target species. If this is your case, you can be sure to apply stock assessment methods with landings of your target species. The problem will arise if this fishery are discarding the species target. I believe that, in this case, you should estimate the discard proportion and explain this clearly when runnig your model.
In general, discards are not of the target species. If this is your case, you can be sure to apply stock assessment methods with landings of your target species. The problem will arise if this fishery are discarding the species target. I believe that, in this case, you should estimate the discard proportion and explain this clearly when runnig your model.
The answer will probably depend on how you propose to estimate MSY.
If discarding practices are stable and if your estimate of MSY is used as an estimate of maximum sustainable _landings_, it might be OK to use only the landed catch. However, if the discarded proportion of the target species is anything but negligible and if it changes substantially over time, then I agree with Carlos: you would need to include estimates of discards. Indeed, you should really include fish killed by fishing that are never caught, unless those are a negligible quantity (which they often are).
But don't get too hung up on these details. Some fishery assessments are reasonably precise and it is worth worrying over minor biases. Sadly, most assessments are massively uncertain (when they are not just massively wrong) and attention should go on the major sources of uncertainty, not the minor ones.
I am using:
Martell, S., and R. Froese. 2013. A simple method for estimating MSY from catch and resilience. Fish and Fisheries:504–514.
for data-poor / no survey areas. Hopefully be pushing out that manuscript soon.
Other well treaded options are MacCalls Depletion based methods from NOAA SWFSC:
Dick, E. J., and A. D. MacCall. 2011. Depletion-Based Stock Reduction Analysis: A catch-based method for determining sustainable yields for data-poor fish stocks. Fisheries Research 110:331–341.
MacCall, A. D. 2009. Depletion-Corrected Average Catch: A Simple Formula for Estimating Sustainable Yields in Data-Poor Situations. ICES Journal of Marine Science: Journal du Conseil 66:2267–2271.
For an overview of current thoughts on catch/CPUE based methods these are all good references:
Berkson, J., and J. T. Thorson. 2014. The determination of data-poor catch limits in the United States: is there a better way? ICES Journal of Marine Science: Journal du Conseil:fsu085.
Carruthers, T. R., A. E. Punt, C. J. Walters, A. MacCall, M. K. McAllister, E. J. Dick, and J. Cope. 2014. Evaluating methods for setting catch limits in data-limited fisheries. Fisheries Research 153:48–68.
Cope, J. M., J. T. Thorson, C. R. Wetzel, and J. DeVore. 2014. Evaluating a prior on relative stock status using simplified age-structured models. Fisheries Research.
Dowling, N. A., C. M. Dichmont, M. Haddon, D. C. Smith, A. D. M. Smith, and K. Sainsbury. 2014. Guidelines for developing formal harvest strategies for data-poor species and fisheries. Fisheries Research.
Rodríguez-Domínguez, G., S. G. Castillo-Vargasmachuca, R. Pérez-González, and E. A. Aragón-Noriega. 2014. Catch—Maximum Sustainable Yield Method Applied to the Crab Fishery (Callinectes spp.) in the Gulf of California. Journal of Shellfish Research 33:45–51.
Thorson, J. T., and J. M. Cope. 2014. Catch curve stock-reduction analysis: An alternative solution to the catch equations. Fisheries Research.
Thorson, J. T., C. Minto, C. V. Minte-Vera, K. Kleisner, and C. Longo. 2013. A new role for effort dynamics in the theory of harvested populations and data-poor stock assessment. Canadian Journal of Fisheries and Aquatic Sciences.
Walsh, W. A., and J. Brodziak. 2014. Billfish CPUE standardization in the Hawaii longline fishery: Model selection and multimodel inference. Fisheries Research.
If discards are an important part of the catches your MSY reference points (MSY, Fmsy, Bmsy) estimations can be biased. MSY reference points depend on the exploitation pattern, i.e. the relative proportion of fish caught at age (or size). Even more, these can interplay with growth, M or maturity. So, the impact is case specific. A good approach in this situation is to develop some king of sensitivity analysis to kow to what extend the asumption about discards impact on your reference points. For instance, make a few credible figures about the proportion of discards and their size (or age) and explore how the reference points change. In this way you can answer yourself whether ignoring discards has impact and whether it is worth to make an extra effort to monitor discards.
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