Fraser River Sockeye Fisheries and Fisheries Management - Cohen ...

period of high harvest rates) and the text seems to confirm that approach. An alternativeapproach would be to use a "phase plot" in which recruitment (R t ) is plotted on the x-axis andexploitation rate (ER t ) on the y-axis. Recognition of the time-series nature of the data can beaccounted for by connecting each (R t ,ER t ) pair with a line segment. Data points lining up alonga horizontal line indicate that harvest rates are independent of recruitment, and therefore, oneonly needs to evaluate whether the average harvest rate is too high, or too low according towhether the implied escapement is above or below optimal levels (however that is defined).Data points forming a negative relationship, in which high exploitation occurs at low abundanceand low exploitation occurs at high abundance, is a sign of serious and potentially destabilizingover-harvesting. Again, the severity of potential impact depends on the absolute exploitationlevels, but such analyses provide a better indication of over-harvesting risks than qualitativedescriptions of temporal patterns.LGL Response: We examined the relationship between recruitment (R) and exploitationrate (ER) as suggested by Dr. Cox. We prepared plots for each run-timing group by cycleyear (see Figures Cox 1-4, below). Most of the 16 plots (4 timing groups times 4 cycleyears) did not show any clear relationship between R and ER. The 2006 cycle year(dominant cycle) for the Early Summer timing group was the only instance whereabundance had increased with declining ERs (i.e., indication of potential over-harvesting).The ERs were relatively high (70-90%) and recruitment was relatively low (