Effects of rainfall on the population of shrimps Penaeus monodon fabricius in Segara Anakan Lagoon, Central Java, Indonesia

Abstract

Segara Anakan Lagoon (SAL) widely recognised as traditional fishing ground for many fisheries organism and is located at a area with a high rainfall. The objectives of the present study are to determine the effects of rainfall on the distribution of Penaeus monodon Fabricius in the SAL and/or mangroves waters and to explain the cause of the yearly fluctuations in the shrimp catch in this area during 13 years period (1998 -2011). The effects of rainfall on the local distribution and abundance of the shrimp in the SAL, Cilacap, Central Java, Indonesia, were examined for three periods by Anco method: first period (of commercial catch production, 1998 - 2011), second period (December 2010- November 2011) and third period (December 2011 - April 2012), as part of a shrimp fishery and eco-biology study in this region. The marked increase in the rainfall from 557 mm in East Monsoon (June-August) to 1,225 mm in second transition season (September-November) and West Monsoon (December- February) in the Segara Anakan region enhanced the seasonal movement of shrimp into the fishing ground zone IV and produced an initial increase in the abundance of adults (CL > 25 mm) in the region (312 to 2,630 individuals). This initial increase in adult abundance enhances the shrimp reproductive potential and the heavy rainfall indirectly assists the recruitment of young shrimp to the estuary and their growth and survival to increase shrimp abundance in the following year. Lower rainfalls (July- August-September) adversely affect shrimp population and usually result in smaller size of the population (312 individuals). Statistical analysis on relationship between shrimp catch with annual rainfall showed highly significant at 1% level.