Vessels participating in exploratory fisheries for Dissostichus spp. are required to conduct the tagging program described in Conservation Measure 41-01, Annex 41-01/C. The program requires, inter alia, that the length frequency of Dissostichus spp. tagged matches the length frequency of the catch of each species of Dissostichus. The degree to which this match is achieved is evaluated using the tag overlap statistic (Annex 41-01/C, footnote 3). This statistic ranges from 0-100%, and a high value (> 60%) indicates a good match between the length frequency of tagged fish and the length frequency of fish caught. A vessel's tag overlap statistic is calculated for each subarea and division fished, and applies across the whole season.

Each vessel is required to achieve a minimum tag overlap statistic of 60% for each species of Dissostichus with a catch of more than 10 tonnes in a fishery. However, for any vessel fishing for Dissostichus spp. which meets the required tagging rate, the minimum tag overlap statistic of 60% shall not apply for a species of Dissostichus for which less than 30 fish have been tagged.

The calculator allows vessels to monitor changes in tag overlap statistic during a fishing trip. The calculation in this spreadsheet is indicative only, and it is the responsibility of the vessel's Flag State to ensure compliance with this statistic and related  requirements of Conservation Measure 41-01.The calculator also includes an indicative tagging rate (number of fish tagged per tonne of green weight caught) for each individual species, and for both species combined.

The calculator uses the catches reported in the Fine-scale catch and effort data (C2 longline fisheries) (1.37 MB) and the lengths measured by the scientific observer and reported in the observer Longline fisheries data and cruise report forms (857.79 KB) (biological data form L6 and tagging form L11). To enable this calculation to be made in this spreadsheet, is it essential that all data in forms C2, L6 and L11 are reported in the appropriate numeric and date formats, and that the 'haul number' reported in the C2 data corresponds with the 'Set number' reported in the L6 and L11 data. 

For accurate estimation of the tag overlap statistic, please ensure that all hauls reported in the C2 data are also reported in the observer logbook, and vice versa.

The calculator is limited to a maximum of 250 hauls, 6000 length measurements, and 1000 tagging records.