Analysis of the space-time variation of emperor (Lethrinus) in Omani waters
The contribution of this study is a systematic analysis of the space-time patterns in distribution of emperor in Omani waters. Geographical Information Systems (GIS) are used to provide a qualitative description of the relationships between monthly fish distribution and abundance (based upon commercial and traditional catch records) with monthly data on sea surface temperatures, salinity and water depth for the period 1996-2004. In addition a General Additive Model (GAM) is used to provide quantitative descriptions of the spatial relationships between the distribution of emperor abundance and the environmental variables. Further, both GIS and GAM methodologies are used to identify and explain space-time patterning in the spawning season of Lethrinus nebulosus in the Arabian Sea. GIS techniques are used to analyse the spatial performance of the models and to provide an independent verification of the GAM results. In regard to spawning data collected as part of a recent biological survey (2000-2001), the work evaluates typical space-time patterns in the spawning season for Lethrinus nebulosus in Omani waters and further explores both the relationship between spawning and maturation and controls on maturation. Analysis shows that the emperor is more abundant in the southwest of the Omani sector of the Arabian Sea than the northwest; temporally, the peak season for high abundance of emperor lies between September and December. Additionally, the GAM fitted data clearly indicates a seasonal effect on Gonado Somatic Index whereby the most strongly positive effect is during August to October and the starting point of the first sexual maturity is a length of around 35 cm.