Screen 8: Percentage of results obtained by different methods of estimating mean weights (EMWs) for fish species

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Reliability ranking of the EMWCapture (t)% of captureNumbers (lower)Numbers (upper)% of total numbers (lower)
in millions
% of total numbers (upper)
in millions
4 (upper EMW only obtained)2,165,745354,93458,48762
5232,752< 12,3123,153< 1< 1
5 (based on max length)11,485< 1912< 1< 1
6363,824< 12,6053,993< 1< 1
7235,387< 16,19228,97811
Multi-species categories5,400,678778,876438,735816
Total capture with EMWs53,025,42869677,1861,974,0797072
Total capture without EMWs24,362,89431296,785761,5003028
Total fish capture77,388,322100973,9712,735,579100100

This screen has been developed for evaluation purposes. It shows the proportion of the estimate of numbers obtained in this study for 1997-2007 which were calculated for:
1. Single-species FAO categories by methods at each level of reliability ranking
2. Multi-species FAO categories
3. Species for which an estimated mean weight (EMW) could not be obtained.

It also shows the % of total capture by weight that was used for these various calculations. The 7 reliability rankings are detailed in the table below.

Key for reliability ranking of methods of estimating mean weights

Reliability Ranking Type of data used Reliability of
length-weight conversion data used
(if any)
1 Average weight data Not applicable
2 Common or typical weights, or normal weight ranges Not applicable
3 Average, common or typical lengths, or normal length ranges Good
4 Less good
4 Any of the above where only the upper end of the estimated mean weight range was obtained
5 Average weights based on maximum weights Not applicable
5 Average weights based on maximum lengths Good
6 Less good
7 Average weights based on (rank 1-3) data for a similar species Not applicable (not used on the species in question)