Introduction

Read in the data with harvest control rules for each of 4,713 fisheries:

MEYdat = read.csv('../Data/Kobe MEY data for chris.csv',stringsAsFactors=F)

Read in, but suppress, a function for calculating weighted geometric means:

The number of unique species is 1133, the number of total stocks is 4713, and the number of stocks with \(F/F_{MSY}>10\) is 118.

Big vs. Small Fisheries

Using a cutoff of \(MSY>\) 3000, there are 1098 Big fisheries (which comprise 98% of global MSY potential) and there are 3615 Small fisheries (which comprise 2.2% of global MSY potential). The median \(B/B_{MSY}\) for Big fisheries is 0.89, and the median for Small fisheries is 0.74, so median biomass in Big fisheries is 20% higher than in Small fisheries.

Bmey vs. Bmsy and Fmey vs. Fmsy

For all stocks, we find that \(B_{MEY}>B_{MSY}\). The mean value of \(B_{MEY}/B_{MSY}\) is 1.3. This implies that \(F_{MEY}<F_{MSY}\). The mean value of \(F_{MEY}/F_{MSY}\) is 0.73.

Current status: B/Bmey and Current F/Fmey

The current median value of \(B/B_{MSY}\) is 0.77. Using the \(MEY\) reference points, this value decreases to \(B/B_{MEY}=\) 0.57. The current median value of \(F/F_{MSY}\) is 1.5. Using the \(MEY\) reference points, this increases to 2.1. Under \(MSY\) targets, the fraction of global stocks with \(B<B_{MSY}\) is 68%. Under \(MEY\) targets, the fraction of global stocks with \(B<B_{MEY}\) is 81%.

A version of a Kobe plot under MEY reference points is provided below, where the diamond gives the median and square gives the \(MEY\)-weighted geometric mean:

Lost Yield from MEY Reference Points

If we deviate from \(B_{MSY}\), then that will entail a reduction in steady state harvest. How much yeild is lost from \(MEY\) targets, rather than \(MSY\) targets? We find that the mean value of \(MEY/MSY\) is 0.95, which implies a mean lost yield of 5%. A histogram of lost yield is presented below:

What Fraction of Fish Catch is “Sustainable”?

Suppose we think of a fishery as being “sustainable” if it is not of “conservation concern”. What fraction of fish catch comes from this quadrant?

The total catch from our dataset from “conservation concern” stocks is 310^{7}. The total catch from “sustainable” stocks is 310^{7}. This implies that the fraction of catch that is “sustainable” is 50%. The Kobe plot below reproduces the \(MEY\) Kobe plot, but where dot size (and color) is directly proportional to current catch.