Length-frequency data approaches to evaluate snapper and grouper fisheries in the Java Sea, Indonesia

Abstract

Indonesia is the most important producer country of snapper and grouper species worldwide, with a notable increase in landings over the past decades. The Java Sea is one of the most frequently fished areas for these species in Indonesia, but in 2016 a decrease in landings was observed. This study applied two approaches (Length-based Indicators and Length-Structured Growth-Type-Group Model) to assess the status of snapper and grouper fisheries in the Java Sea, using length-composition data from the commercial fishery and covering multiple gears with different selectivity. The work focused on the dominant species in the catches: Malabar blood snapper (Lutjanus malabaricus), Areolate grouper (Epinephelus areolatus), Crimson snapper (Lutjanus erythropterus), and Goldbanded jobfish (Pristipomoides multidens). Considerable differences were observed, related to the type of gear used. Catch data obtained from the longline fishery presented good stock status indicators for all species studied. The spawning potential ratio (SPR) estimates calculated for Malabar blood snapper and crimson snapper indicated that these species are currently fished in the Java Sea at unsustainable levels (below 30 % SPR) by the dropline and mixed-gear fleets, while areolate grouper and goldbanded jobfish are not overfished (above 30 % SPR). For both methods, bias in Linf and, secondarily, bias in M/K have a stronger influence on the indicators values, in particular for the proportion of individuals above the length of optimal yield + 10 % (Pmega) estimates and SPR, than bias in Lmat values. This study highlighted other areas where improvements are critical to ensure the sustainability of the snapper and grouper fisheries in the Java Sea.