Application of GIS technique in the studies on fish assemblages in Shatt Al-Arab River, Basrah, Iraq

: The present study has examined the spatiotemporal varieties of the demographics of the Shatt Al-Arab River fishes and their relation to some ecological components. The aim is to forecast these groups in the unexplored parts of the waterway with an emphasis on environmental indices of diversity. Three sites in the river were selected as an observation and study of these species, which lasted from March 2019 to February 2020, the study dealt with factors affecting fishes, as Water Temperature (WT), Dissolved Oxygen (DO), Potential Hydrogen Ion (pH), Salinity (Sal), and Transparency (Tra). Gill nets, cast nets, hooks, and hand nets were adopted to collecting fish. The results indicated that the fish population comprises 60 species representing 13 orders, 28 families, all species belonged to Osteichthyes except for one (Carcharhinus leucas) which belonged to Chondrichthyes. Cyprinidae is the prevalent family embraced by nine species. WT (12.1- 33.4°C) has a considerable influence on the total number of species and individuals to the north of the watercourse. However, salinity (0.9- 8.7 mg/L) was regarded as the essential impact on the composition, distribution, and abundance of species in the rest sites. Planiliza abu was the most abundant species attaining 20.21%, followed by Oreochromis aureus (16.41%), and Carassius auratus ranked (15.92%), the dominance (D3) value was 52.54%. The results of the current study showed that most of the diversity index values are considered a moderate status. On the other hand, the majority of the richness index values are viewed as semi disturbed status in all stations, while most of the values recorded of the evenness index are deemed as semi-balanced status. The application of GIS technique by using the ordinary kriging method showed high efficiency in the Shatt Al-Arab River. Therefore, this technique can be employed in environmental studies of fishes.


Methodology and Materials:
Fish specimens were counted and classified by several authors [17][18][19][20] . We used the fish classification system in Eschmeyer's Catalog in Table 1 according to the evolutionary level of fish families. Fish assemblage analysis (in the three sites) was carried out by the following processes and indices: relative abundance 21 , domination (D3) 22 . Fish species were split (according to their occurrence in the monthly samples) into three categories 23 : resident (common) species (nine -12 months), seasonal (six-eight months), and occasional (one -five months). The CANOCO program (version 4.5) was utilized for: measuring the ecological indices (diversity, evenness, and richness), doing the multivariate analysis of data among months, and plotting CCA ordination. The SPSS program (version 20) was used for all statistical analyses of the collected data. However, the ArcGIS 10.4.1 program was applied by the spatial analysis method. The Spatio-temporal variability of fish data was predicted by the ordinary kriging interpolation method, with a spherical semivariogram model using the spatial analyst tool in ArcGIS. The ordinary kriging method is the most basic way of kriging interpolation, which allows for applying a statistical model that included autocorrelation. Moreover, using these interpolated values, photomap layers for each parameter were developed, which show the spatial distribution pattern of these fish across the river. Furthermore, a buffer tool was used to display the map features more clearly for the study area.  Sixty fish species gathered from the investigated sites in the Shatt Al-Arab River belong to 13 orders, 28 families; 12 of them are exotic, 19 freshwater, and 29 marines. All species relate to Osteichthyes except for one (Carcharhinus leucas) impute to Chondrichthyes. The dominant family was Cyprinidae, which comprised nine species, followed by Xenocyprididae, Leuciscidae, and Mugilidae (four species). However, five families take part by three species for each (Engraulidae, Cichlidae, Sillaginidae, Sparidae, and Sciaenidae), five families formed by two specimens (Clupeidae, Gobiidae, Carangidae, Poeciliidae, and Aphaniidae), and the rest families represented by one species each (Table 1).   Fig. 3 reveals that the spatial pattern of the total number of species in Shatt Al-Arab River, with note moral differences (P<0.05, F=2.874), was found between Station 1 and 3. Thirty-six species recorded at station 1, they differed from nine in January to 25 in May. At station 2, Forty-six species found, range from 15 in May to 28 in October. Fifty-five species represented at station 3, which vary from 17 in March to 28 in September. Sixty species did collect from the study site fluctuated from 27 in March and December to 42 in August (Fig.4). A total of 25413 fish specimens were captured from the study stations ranged from 1480 in January to 2943 in August. The number of individuals at station 3 emerged to differ significantly (P<0.05, F=6.075) with other stations. An equal of 7086 fish was recorded at station 1, which varied from 336 in December to 777 fish in August. Besides, 8228 fish were caught in station 2, fluctuated from 545 in November to 1170 fish in February. Meanwhile, 10099 fish were registered from station 3, improved from 483 in January to 1325 fish in August (Fig. 4).

Relative abundance of fish
During the study period, Planiliza abu was represented 20.21% as a dominant species in Shatt Al-Arab River. It fluctuated from 10.25% in March to 35.43% in February. Oreochromis aureus comprising 16.41% of the gathering changed from 9.54% in June to 27.33% in November. Carassius auratus reached 15.92%; its abundance varied from 10.22% in April to 21.89% in July. According to the Dominance index (D3), these three species formed 52.54% of the total number of species in the Shatt Al-Arab River ( Table 2).

Species
Cod

Fish species occurrence
Depending on their frequency in the monthly samples, species existing in Shatt Al-Arab River are classified into three groups (Table 3): Common species, represented by 24 species, 13 of them appeared throughout the study period. The common species formed 40% of the whole number consist of native, marine, and exotic species. Thirteen fish species were recognized as Seasonal species, three of their presence in eight months. This group formed 21.67% of the total number of collected species. Finally, 23 species designated as Occasional two of them did represent in five months. Subsequently, Occasional classes reached 38.33% of the whole abundance of species (Fig. 6).    The number of alien species was equal in all locations reaching 12 species. They fluctuated from six in December and January to 10 in August at station 1. The minimum number (7) in station 2 appeared in five months, namely March, April. June, January, and February. While the highest number (9) in July and September. Finally, five exotics recorded in October, November, and January at station 3 increased to nine in April and February (Fig. 8). The geographical distribution pattern of the total number of marine species in Shatt Al-Arab River during the study period is shown in Fig. 9. The lowest number (8) registered in station 1 varied from one in November to six in May and July. Seventeen marine fish in station 2 ranged from two in March to 10 in October. Whereas the highest marine species number was 28 detected in station 3, change from five in March to May, to 12 in August to November and January. 2.71 in May to 3.33 in October, and the evenness index changed from 0.59 in December to 0.78 in January (Fig 11). Meanwhile, at station 3, the diversity index increased from 1.94 in February to 2.62 in September. The richness index ranged from 2.83 in March to 3.33 in September. Also, the evenness index varies from 0.59 in February to 0.79 in June (Fig 12).

Multivariate analysis
The canonical correspondence analysis (CCA) ordination plots epitomized the relationships among the available fish species, individuals, and the ecological elements in the survey sites. In station 1, water temperature was a greater influence factor on the total number of species and individuals compare with other agents (Fig. 13). It was a strong positive correlation with an abundance of species (r= 0.81) and individuals (r= 0.52). However, transparency was a powerful negative correlation with the total number of species (r= -0.76) and individuals (r= -0.44). Salinity (In station 2) was the main impact factor on the total number of species (r= 0.82), followed by water temperature (r= 0.57). On the other hand, pH was the most affective agent (r= 0.64) on the total number of individuals compared with other factors (Fig. 14). However, in station 3 salinity was the greater impact factor (r= 0.74) followed by transparency (r= 0.43). While water temperature was a greater influenced agent (r= 0.57) than others on the number of individuals (Fig. 15).  Table 2).  Table 2).  Table 2).

Discussion:
Interestingly, the capacity of some fish species to modify to diverse ecological conditions 24 . P. abu is considered a native species for a long-time in this area 18 . Likewise, this enabled P. abu to prevail in Shatt Al-Arab River in this study, which appeared in all study periods. This result does not coincide with most late studies (during the past decade) which indicate other species' dominance 5, 6, 13, and 14 .
As these studies showed, the abundance of species is impressed by aquatic environmental changes. Due to the overfishing, the spread of some invasive species, and lack of water levels lead to saltwater intrusion from the Arabian Gulf. Therefore, that influenced the presence of resident species such as P. abu and the composition of the fish community. Although O. aureus was registered for the first time (in 2009) in Iraq 25 , it managed to adapt to all environments and compete with local species. However, it ranked the second abundance in this study, this is consistent with the study of Mohamed and Abood 26 , which indicated that it is one of the dominant species in Shatt Al-Arab River. One of the most important reasons for the widespread of this species is the high tolerance to various environmental conditions 27 and the reproductive activity throughout the year (This applies to other species that belong to the Cichlidae family). Moreover, C. auratus is an alien species apparition in water bodies in the early nineties 28 , also adapted to prevailing environmental conditions and spread rapidly. Consequently, it ranks third in this study in all locations, which concurs with the conclusions of most previous studies that confirmed the dominance Schiphouwer et al. 29 mentioned, invasive species have different life capabilities, which enabled them to expand their spread to affect the composition of the fish community through competition, predation, and interference. That is the main reason for the sharp decrease in the density of the native species. They were recorded with greater abundance in previous studies, that attribute to the reduction of water levels due to the establishment of many dams on the Tigris and Euphrates rivers in Turkey 30 , which lead to a reduce the flood seasons. That is a vital factor in the revival of areas for the reproduction of native species (freshwater species).
A great abundance of alien species, overfishing, forbidden fishing methods, and catching fish in the breeding times contributed to a low population density of native species. Interestingly, the spatial analysis results of the number of fish species, individuals in Figures 3, 5, 7, 8, and 9 showed a high ability to predict the expected values in the unexamined areas of the river based on the data recorded in the studied location. That helps tremendously in predicting the status of the fish community in the short and long term, diversity conservation, ecosystem, and the rational management of rivers. It also makes it easier for researchers to work and reduces the effort and time spent on rivers environmental survey. However, the spatial interpolation by the ordinary kriging method showed high efficiency in Shatt al-Arab River, as it does not contain barriers that prevent the movement and spread of fishes. Thus, this technique can be highly employed in environmental studies of fish.
Despite the appearance of 24 species in most of the months of the study (common species), the species that formed a relative abundance of more than 1% did not exceed nine species, including five exotics, five marines, and two freshwater species. The reason may refer to the change of fish community nature because of the rising of alien species number dwelling in Shatt Al-Arab River.
Noticeably, results showed an increase in the portion of marine species in fish populations, which enter the river for reproduction, feeding, or nursery. This aspect coincides with most researchers as Roberts et al. 31 , Mohamed et al. 32 , and Kindong et al. 33 . Marine species are penetrating the middle and lower reaches of Shatt Al-Arab River, and their numeral reduces towards the upper reaches. Likewise, it predominates in station three formed 50.9% (28 species), the usually dominant species was Tenualosa ilisha, which penetrates the river to breeding when the rise of temperature.
As specified by Jorgensen et al. 34 and Hussain et al. 35 , most diversity values recorded (in this study) from the sites can be considered moderate status, rare and poor status at stations 1, 2, and 3 (especially in December). Fish diversity values less than two were recorded in all sites which may be ascribed to changes in environmental conditions in some months that affect the numbers and types of fish. There were slight variations in the values of the richness index recorded in this study, considered as semi disturbed in all stations. By contrast, most of the evenness values state recorded in Shatt Al-Arab River was deemed as semi-balanced, despite the rare ones in balance status from station 1 in January. Indeed, most evenness values ranged between 0.59 and 0.79, indicate the absence of dominance.
Water temperature is a principal factor in controlling the distribution and abundance of living organisms and impacts the physical properties of water. Through the CCA plots, we can observe (at station 1) that water temperature was the prime variable that influences the fish community structure. That agrees with the findings of Lazem and Attee 36 in their studies as concluding that water temperature has the main effect on the presence of fish in freshwater. Likewise, Kim et al. 37 , Walden et al. 38 , and Liu et al. 39 pointed out that plankton, algae, and invertebrates thrived with the rise of temperature, providing an important food source in the water body, which encourages the attraction of fish species and increases their numerical density. In contrast, salinity is the main factor that affected the composition of fish at station 2 and 3, as promotes to excess the entry of marine fish. That is evident by the rise of the number of species in these two sites compared to the first site. So, salinity is considered the prime variable of the spatial distribution of fishes. Despite the significant increase in water drained in Shatt Al-Arab River stream during the study period, which did not occur for many years ago (40), the salinity values did ascend in some months, especially in the second and third stations. The reason may be attributed to the floods that wash the soil and Agricultural lands, then mix with the water coming to the river. and images, which are not mine, have been given the permission for re-publication attached with the manuscript. -The author has signed an animal welfare statement. -Ethical Clearance: The project was approved by the local ethical committee in The Open Educational College.