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Spanner crabs Ranina ranina, also known as red frog crabs in Asia and kona crabs in the United States, inhabit sandy substrates in shelf waters throughout the tropical and subtropical Indo‐Pacific region from the western Indian Ocean (de Moussac and de San 1987) to the northcentral Pacific Ocean (Onizuka 1972; Brown et al. 1999). These large, edible crabs are the subject of distinct but relatively small fisheries throughout this region, including the Seychelles (Boullé 1995), Japan (Sakai et al. 1983), Philippines (Tahil 1983), Hawaii (Onizuka 1972; Brown 1984; J. P. Vansant, University of Hawaii, unpublished data), and Australia (Brown et al. 1999). Information on how, and indeed whether, many of these fisheries are managed is scant. Apart from Queensland, Australia, where output controls have been introduced, input controls on fishing apparatus are believed to be the norm where controls exist.
In Australia, adult spanner crabs are targeted by using simple, inexpensive baited tangle nets (dillies) placed on the sea floor. The nets are typically about 1 m2 in area, baited with Australian sardine Sardinops neopilchardus, and deployed on a set of groundlines for periods ranging from 30 min to 2–3 h. The spanner crabs' broad, flattened appendages and elongated body shape enable them to burrow rapidly and swim efficiently (Vicente et al. 1986) but also render them susceptible to this method of fishing. The spanner crabs' mobility allows them to be attracted to bait from considerable distances of up to 70 m (Hill and Wassenberg 1999), and the terminal segments of their legs easily become enmeshed in the tangle nets (Kirkwood and Brown 1998). This fishing apparatus is surprisingly size selective; it is unusual to catch a spanner crab smaller than 50–60 mm rostral carapace length (RCL; Brown et al. 1999; Kirkwood et al. 2005).
While the species has a wide depth distribution from the intertidal to at least 100 m, the commercial catch is taken principally from depths between about 30 and 80 m. There is a marked sexual disparity in size, with male spanner crabs reaching 150 mm RCL while females rarely exceed 120 mm RCL...