Fisheries Research 99 (2009) 151–158 Contents lists available at ScienceDirect Fisheries Research journal homepage: www.elsevier.com/locate/fishres Reconstructing historical trends of small pelagic fish in the Java Sea using standardized commercial trip based catch per unit of effort Massimiliano Cardinale a,∗ , Duto Nugroho b , Lars Hernroth a a Institute of Marine Research, National Board of Fisheries, P.O. Box 4, SE-45321 Lysekil, Sweden b Research Institute for Marine Fisheries, Agency for Marine and Fisheries Research, Jl. Muara Baru Ujung Jakarta 14430, Indonesia article info Article history: Received 29 January 2009 Received in revised form 19 May 2009 Accepted 21 May 2009 Keywords: Java Sea Pelagic fish CPUE GAMs abstract Pelagic fish stocks in the Java Sea have been exploited intensively since the beginning of the 1970s. However, due to the effect of increased fishing power of the fleets and the changing nature of spatial and temporal distribution of the fishing effort, assessment of stock trends based on commercial data of catch and effort requires the standardization of both effort and catch data. Here we present the first attempt to reconstruct a standardized time series of commercial catch per unit of effort (CPUE) for the main pelagic species exploited by the purse seine fleet in the Java Sea. The results showed that all the stocks analysed have largely declined since the beginning of the 1990s. For bigeye scad, Indian mackerel and sardine, current estimates are only between 3 and 19% of the maximum observed value while round scads and spotted sardine biomass estimates lie between 18 and 34%. However, our assumptions about the effect of lamp power and level of creeping and the fact that the influence of fish density on catchability and the effect of targeting were not taken into account thus observed decline is a rather conservative estimate of the real decline of the stocks. If effective management actions are not put in place as a matter of urgency in the Java Sea for small pelagic fisheries, one runs the risk of adding those species to the long list of overexploited stocks of the world oceans. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The Java Sea forms part of the Sunda Shelf and covers an area of 450,000 km 2 . The environmental features in the area are governed by the monsoonal cycle, which affects the hydrological conditions (Durand and Petit, 1995). About 60% of the Indonesian fishermen operate within the Java Sea and adjacent waters and most of the fisheries activities in this area are constituted by the small scale fish- eries. Particularly, the Java Sea is one of Indonesia’s most productive areas for commercial fisheries of small pelagic species (Sujastani, 1978; Widodo, 1988; Nurhakim, 1995) and purse seines have been the most popular fishing gear to harvest small pelagic fish species in this area since decades. Such a fishery has existed in the Java Sea since the 1970s and several improvements on auxiliary fishing gears were developed in connection with the expansion of fishing grounds (Atmaja, 2002; Potier et al., 1997). In most parts of the Java Sea, in which the medium and large Purse seine fleets oper- ate, the shallow sea floor consists of a vast sand and mud bank ranging from 50 to 70 m in depth (Wyrtki, 1961; Durand and Petit, 1995). Recent annual statistical data (Anonymous, 2008) showed that total landing of small pelagic fish in 2006 was around 27% of ∗ Corresponding author. Tel.: +46 523 18750. E-mail address: massimiliano.cardinale@fiskeriverket.se (M. Cardinale). the total Indonesian fish production with a value of 19% (about half a million US$) of the total national value. The estimated number of purse seiners registered along the coast of the Java Sea is around 30% of the total number and out of Indonesia’s 2.2 million fisher- men, it is estimated that 20% significantly depend on the Java Sea (Anonymous, 2008). Several previous assessments have been done to describe sta- tus and trends of exploitation levels of several pelagic species, i.e. round scads (Decapterus spp.) chub mackerel (Rastrelliger spp.), sardine (Sardinella spp. and Amblygaster sirm), bigeye scads (Selar crumenophthalmus) and trevally (Selar spp.) applying surplus pro- duction, biological and biomass models (e.g. Sujastani, 1978; Nurhakim et al., 1987; Sadhotomo and Widodo, 1992; Sadhotomo, 1998; Widodo, 1988; Atmaja and Nugroho, 2005; Atmaja, 2006) on aggregated landing and effort data without accounting for the increase in fishing efficiency of the fleet that has occurred continuously since the 1970s. Atmaja and Nugroho (2005) stated that during the 1980s spotlight and floating FAD replaced station- ary FAD (Fishing Aggregating Device). In the last decade average engine power increased from 90 to 320 Hp and it was supported by increased spotlight intensity from 7500 to 20,000 W, further increasing the fishing capacity of the fleet. Substantial histori- cal data available indicated likely over-exploitation of the marine resources in the area (i.e. Nurhakim, 1995). However, considering that pelagic fisheries usually show a strong hyper-stability of the 0165-7836/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2009.05.015