Lunar Cycles, Catchability of Penaeid Shrimps and Implications for the Management of the Shrimp Fishery on Sofala Bank in Mozambique

Abstract

This study investigates the relationship between lunar cycles and catch rates of penaeid prawns on the Sofala Bank, where the fishery occurs for 6.5 to 9 months a year (starting in February or March), and assesses the potential for effort reduction and economic benefits from short-term closures during periods of the lunar cycle with predictably low catch-per-unit-effort (CPUE). A comparative analysis of the day and night CPUE for the daylight-active “banana” shrimps, Fenneropenaeus (Penaeus) indicus and Metapenaeus monoceros and the night CPUE for the nocturnally active Melicertus latisulcatus and Marsupenaeus japonicus was undertaken for each lunar phase and month using two-way ANOVA. Significant monthly variations in CPUE were found in both day and night samples of banana shrimps, for which the CPUE declined throughout the fishing season regardless of time of the day. M. latisulcatus manifested significant variations in night-time CPUE during the lunar cycle, with full moons yielding the lowest catches. This is thought to be caused by the burrowing behaviour of this nocturnal shrimp which decreases its catchability. The benefits of fishery closure during full moons and from June to the end of the fishing season were tested assuming two fishery scenarios of differing duration: a 6.5-month fishery (15 March - 30 August) and a 9- month fishery (15 March – 15 December). These closures resulted in an effort reduction of 5% and 8%, respectively, with corresponding catch reductions of 4% and 6%. However, profitability of the fishing companies would improve by 3% and 7%, respectively, as a result of more efficient trawling.

Keywords: Penaeidae, fishing effort, lunar phases, profitability, spatial closures.