Numerical and Descriptive Assessment of the Fish Assemblage at East Hammar Marsh, Basra, Iraq

Abstract

The fish assemblage at the East Hammer Marsh (EHM) was overwhelmed by alien species and individuals compare to native species. Alien species were successfully established in the EHM over a relatively short time period. Gradual decreases in the occurrence and abundance of native species were recognized owing to the continuous increase in salinity and alteration of the aquatic environment from freshwater/oligohaline to mesohaline/estuarine. The degree of disturbance of the fish assemblage invaded by alien species was quantified on the basis of the native species number and their individuals to the total number of species and total individuals present. Formulas were applied to quantify the scores of occurrence and abundance of both native and alien species ratios. Data on the occurrence and abundance of native fish components in the assemblages were very disturbed 18.2% and totally upset (3.2%). A noticeable decrease in the ratio of native species to alien species and vice versa was accompanied by an increase in salinity during one decay from 2009 to 2024.The highest number of species recorded at EHM was 44 in 2012 and the lowest 21 in 2024.The highest native species occurrence rate was 56% in 2013 and the lowest was 20%. In 2019 .The highest abundance score of the native species was 44% and the lowest was 20%. In contrast, the highest score for alien species was 80%. Higher native occurrence and abundance scores were observed at the inlet marsh station (Al-Sadda) than at the rest of the EHM. The highest turnover rate index was 43.39 and the lowest was 8.19. As the turnover index value increased, more alien species occurred at EHM. In general, a continuous salinity increase changes the constituents of the fish assemblage at EHM, accompanied with increase in the percentage of alien species from 2019 to 2024.