A false positive in the CCAMLR tag overlap statistic arising from low catch volume and consequent limited sample size

The draft CCAMLR compliance report has recorded that when fishing in Subarea 88.2 in 2013/14 the vessel Argos Georgia achieved a tag overlap statistic of 52% rather than the required minimum of 60% as specified in CM 41-01. A review of the data indicates that the number of fish tagged was above the rate per tonne required by CM 41-10, but due to sampling noise the distribution of the length of fish tagged did not match closely with that of the catch resulting in a the overlap statistic, as required by CM 41-01. The overall length range of the two data sets was similar indicating that this was not a case of only small fish being tagged. The low tag overlap statistic is shown to be a sampling artefact and not a compliance issue. WG-FSA 2014 and CCAMLR SC 2014 should consider and discuss cases such as this and others if they have arisen, to determine how to provide advice to the Commission in cases where the noise associated with such low numbers of fish triggers false positives in the tag statistic. It is considered that such events will become more frequent as capacity increases in the Olympic exploratory fisheries and small catches with a consequent low total tag number increase in frequency.