Vol.:(0123456789) 1 3 Fish Sci DOI 10.1007/s12562-017-1126-9 ORIGINAL ARTICLE Efects of net height of crab entangling nets on the capture of targeted economically important portunid species and non‑target species Rizalyn M. Picoy‑Gonzales 1,2  · Harold M. Monteclaro 1   Received: 28 November 2016 / Accepted: 17 August 2017 © Japanese Society of Fisheries Science 2017 Keywords Gillnets · Selectivity · Discards · Bycatch Introduction The blue swimming crab Portunus pelagicus is one of the more important fshery commodities in the eastern tropical Pacifc and western Indian Oceans [1–3]. These crabs are found throughout the nearshore marine and estuarine waters, including sandy, muddy and seagrass habitats, to a depth of at least 50 m [1, 4–6]. Juveniles occur in shallow water bod- ies, such as mangrove creeks and mud fats, while adults are found in sandy substrates at deeper water of up to the 20-m isobath [2, 7]. In central western Philippines, P. pelagicus spawn continuously throughout the year, with peak periods during the frst and last quarters of the year [8]. The aver- age carapace width of maturity is 10.56 and 9.64 cm for females and males, respectively [9], and the average sex ratio is 1:1.2, with 46.1% females and 53.9% males [5]. Areas with soft substrate and gentle slope are common P. pelagicus fshing grounds; consequently, the major fshing grounds in the Philippines are shallow inland waters [1]. Local fshermen use a variety of fshing gears to capture P. pelagicus, but crab entangling nets are among the most common gears used [1, 10]. This gear consists of long rec- tangular netting with diamond-shaped meshes set vertically at the bottom and kept stationary by anchors attached at both ends [10]. However, P. pelagicus fshery has been reported to be declining, with sustainable fshery hampered by several factors, such as irresponsible fshing practices, high bycatch, capture of undersized and berried crabs and other govern- ance issues [1, 11]. The current minimum legal size for cap- ture of P. pelagicus is set at 102 mm carapace width [10]. The high rates of non-target species and capture of juvenile conspecifcs are among the major issues in crab Abstract The aim of this study was to determine the efects of net height on the capture performance of crab entangling nets. Fishing trials were conducted using nets at varying net heights (1) 12 meshes down (MD), (2) 24 MD and (3) 50 MD. A total of 1290 individuals comprising 87 species belonging to 53 families were caught. One-way analysis of variance showed that net height signifcantly afected the various catch parameters, including catch per unit efort (CPUE) of the total and target catch, amount of non-target catch, size of catch and species richness. The use of appropriate net height is a potential technical measure for a selective but still efcient crab entangling net fshery. Lower net height signifcantly reduced non-target catch by up to 70%. Lower net height also decreased the CPUE of target catch such as Portunus pelagicus and Charybdis fer- iatus by up to 65% at 12 MD, but catch at 24 MD was not signifcantly diferent than that at 50 MD. The use of a net height of 24 MD also resulted in the capture of larger-sized P. pelagicus. The richness of the catch species decreased by up to 58% in lower nets. These results are useful to fshery managers and government institutions when developing and/ or improving existing regulations towards a sustainable crab fshery, particularly blue swimming crabs. Fisheries * Harold M. Monteclaro hmmonteclaro@up.edu.ph Rizalyn M. Picoy-Gonzales rizalynpgonzales@gmail.com 1 Institute of Marine Fisheries and Oceanology, College of Fisheries and Ocean Sciences, University of the Philippines Visayas, Miagao, 5023 Iloilo, Philippines 2 Department of Fisheries, Visayas State University–Tolosa, Tolosa, Leyte, Philippines