Requiem for Ricker: Unpacking MSY

Much like the Cornucopia myth of the 19th and early 20th centuries, MSY as a management tool simply won’t go away, regardless of evidence that managing for MSY has not been effective. Consequently, we investigate Ricker’s definition of MSY, focusing on words such as average catch, continuously taken, and existing environmental conditions. To do this, we develop a model for the squid fishery in California; this is probably the last great open access fishery on the west coast of the US. By constructing the model in a step-wise fashion, one is able to illustrate particular points. Insight from the model leads to a deeper understanding of the definition of MSY, particularly that different methods of averaging and explicitly including risk to the stock in MSY may allow MSY to be used in the context of precautionary fishery management. Finally, we summarize results from the Third Mote Symposium that also shed light on this issue. Introduction In his classic book, Ricker (1975) defined MSY: MAXIMUM SUSTAINABLE YIELD (MSY OR YS): The largest average catch or yield that can continuously be taken from a stock under existing environmental conditions. (For species with fluctuating recruitment, the maximum might be obtained by taking fewer fish in some years than in others). (Italics added and understanding the full implications of these words is the point of this paper). However, two years later, Peter Larkin (1977) proposed that we bury MSY: "An epitaph for the concept of Maximum Sustained Yield"