Determination of population stock units of Portunus sanguinolentus (Herbst, 1783) as a non-target species (secondary species) using Truss Network Analysis on Madura Island

Abstract The blue swimming crab is one of the fishery commodities that constitute the major component of Indonesia’s third highest export products after shrimp and fish. The slightly expensive crabs in the market include Portunus pelagicus , which is commonly found in Indonesia alongside Portunus sanguinolentus . However, P. sanguinolentus is considered a secondary species due to the lower catch numbers in the country, specifically on Madura Island. The research about this particular crab is still very limited and the importance of information on secondary species stock units is to restore degraded ecosystems through appropriate programmes. Truss Network Analysis (TNA) was applied to measure the crab’s morphometric characteristics. The Kruskal–Wallis test, cluster analysis, and discriminant analysis were the statistical methods used to identify the stock units. The results showed different characteristics of swimming crabs in four locations on Madura Island, namely in the Bangkalan, Sampang, Pamekasan, and Sumenep Regencies. These indicated that different characteristics exist in male crabs found in Bangkalan, Sumenep, and Sampang, which have the highest level of similarity. In contrast, the females formed two clusters consisting of the groups Sampang and Sumenep, as well as Bangkalan and Pamekasan. The group differences show the potential of all crabs in the four locations to have more than one stock unit, hence their management needs to be differentiated.