Invasiveness risk assessment of non-native species of the redbelly tilapia (Coptodon zillii, Gervais 1848) in Shadegan wetland basin

The introduction of invasive fish species into aquatic ecosystems causes various adverse ecological and socio-economic impacts. The first step in analyzing the effects of these species is to identify the risk. Then, different tools have been developed to identify potential invasive species and evaluate potential degree of their invasiveness to support decision-makers in analyzing the invasive risk of these species. This study aimed to assess the invasive potential of the non-native species redbelly tilapia (Coptodon zillii, Gervais 1848) in the Shadegan wetland basin (the Karun and Jarahi catchments) using some of these tools.

The level of risk for C. zillii in the Trinational risk assessment protocol was determined based on the results of the two components "Probability of Establishment" and "Consequences of Establishment". In the German-Austrian Blacklist Information System (GABLIS), the invasive potential of the species was evaluated according to the distribution in the study area. The non-native species was screened by the Aquatic Species Invasiveness Screening Kit (AS-ISK) model according to the threshold of the assessment area; and the rank of species invasion was calculated based on the probability of species establishment, expansion and environmental effects, using the Harmonia+ method. Also, the climate matching between introduced and native range of the species was carrying out with the Köppen-Geiger climate classification system.

The results of trinational risk assessment indicated that the species posed high potential rank of placing at each step of, introduction, establishment and expansion potential and the possibility of economic and environmental impacts in the study area. The results of the GABLIS protocol showed that the non-native species C. zillii has been widely distributed in the risk assessment area and it placed in blacklist and the subset management list (b3). In the AS-ISK risk assessment, the risk score of the species was 44, that was higher than the tool threshold (22.5) for the study area. This score indicates that this species has a high invasive risk in the wetland. The overall risk score in the Harmonia+ method, which is a function of invasiveness and species impacts, was assessed as high for the redbelly tilapia; based on the results, the risk of establishment and dispersal of this species in the study area is high, and its environmental impacts are significant. Also, there was a high climate match between risk assessment area and the native range of the species in the Köppen-Geiger climate classification system.

The trinational risk assessment methods, GABLIS, AS-ISK and Harmonia+ models were able to show the invasiveness of the non-native C. zillii in Shadegan wetland basin as literature and field evidence demonstrate that the species has exerted strong and adverse impacts on native fishes and local people livelihood in risk assessment area. Given the results of risk assessment methods and the risks posed by this species, it is highly recommended that large-scale control and management measures should be seriously implemented.