CCAMLR has defined Vulnerable Marine Ecosystems (VME) detection thresholds based on the benthos bycatch monitoring. When these thresholds are reached during a single longline fishing operation, the data are reported to the Secretariat to inform the CCAMLR about the potential presence of VME to be protected. Management decisions are triggered out according to various levels. Important catches of sea pens (Pennatulacea, NTW, VME bioindicator) in the 58.4.4b sector have been reported during the CCAMLR SAM Working Group 2018. However, despite the important level of the catches, no VME detection threshold triggering out the establishment of an immediate fishing exclusion zone have been reached. Here, we present the preliminary results and some discussion elements of a study centered on the case of the sea pens, and based on the data collected in the 58.4.4b sector. The results may indicate that (1) detection thresholds may be defined considering the taxa of the VME bioindicators, (2) the detection probability is both linked to the weight/size ratio of the organisms and to the ecology of the taxa.