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 EMW	Capture (t)	% of capture	Numbers (lower)	Numbers (upper)	% of total numbers (lower) in millions	% of total numbers (upper) in millions
1	29,827,298	39	466,638	1,189,305	48	43
2	8,698,096	11	13,487	86,272	1	3
3	3,766,342	5	33,616	111,124	3	4
4	2,323,822	3	18,517	54,021	2	2
4 (upper EMW only obtained)	2,165,745	3	54,934	58,487	6	2
5	232,752	< 1	2,312	3,153	< 1	< 1
5 (based on max length)	11,485	< 1	9	12	< 1	< 1
6	363,824	< 1	2,605	3,993	< 1	< 1
7	235,387	< 1	6,192	28,978	1	1
Multi-species categories	5,400,678	7	78,876	438,735	8	16
Total capture with EMWs	53,025,428	69	677,186	1,974,079	70	72
Total capture without EMWs	24,362,894	31	296,785	761,500	30	28
Total fish capture	77,388,322	100	973,971	2,735,579	100	100

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.

fishcount.org.uk

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	Average, common or typical lengths, or normal length ranges	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	Average weights based on maximum lengths	Less good
7	Average weights based on (rank 1-3) data for a similar species	Not applicable (not used on the species in question)