Exploring the use of Length Based Indicators for Blue Shark in the Indian Ocean

Blue shark (Prionace glauca) is the pelagic sharks most frequently captured in pelagic fisheries. It is considered one of the main shark species in tuna-RFMOs worldwide, and the species for which more data is available, including size distribution data. This paper presents an alternative method for providing a snapshot assessment of status, with the development of length based indicators (LBI) and comparison to reference points derived from life-history and ecological theory. The data used came from the last IOTC blue shark stock assessment carried out in 2017. This exploratory analysis revealed some differences between fleets over different components of the stock, but in general met the indicators expectations with the stock being considered in "good" status according to most of the reference points. There were some inconsistent results across different data sources, indicating that issues of gear selectivity and/or differences in the spatial distribution of the fleets in relation to various components of the stock may be influencing the LBI. There is the need for further interpretation of the data in relation to the fishery and spatial structure of the stock, as well as more work directed to determine the appropriateness of the use of those reference points for elasmobranchs, taking into account that they were derived mostly for teleost and shellfish stocks. However, and even thought this is a preliminary exercise at this point, we hope that it provides additional useful information for the advancement of the blue shark management and conservation in the Indian Ocean.