Composition, seasonality and abundance of fishes in the Shatt Al-Basrah Canal, an estuary in Southern Iraq

Abstract

A total of 8245 fishes from 47 species that weighed 226·3 kg were captured over the 12-month period (February 1985 to January 1986) in the Shatt Al-Basrah Canal, a subtropical man-made estuary in Southern Iraq. The most abundant species was Liza subviridis comprising 59·6% of total number and 40·0% of total weight. Acanthopagrus latus, Thryssa malabarica and Aspius vorax together formed 17·71% of total number and 14·48% of total weight. The total number of individuals rose in spring with a peak in April. Numbers of species fluctuated from eight in January to 33 in September. Examination of fish species associations showed that there were more species in the seasonal (17) and occasional (24) components and fewer in the regular (6) component. The species richness index was greatest from June to October, with a peak (5·32) in September, and lowest (1·33–1·87) from January to April. The Shannon-Wiener diversity index ranged from 0·49 in March to 2·84 in September for numbers, and from 0·74 in January to 2·63 in September for biomass. The relative diversity index fluctuated from 0·09 in March to 0·47 in September for numbers, and from 0·14 to 0·43 for biomass for the same months. The evenness index varied from 0·07 in March to 0·50 in September.