Invasiveness risk assessment of non-native fishes using the AS-ISK model in the rivers of the southern basin of the Caspian Sea

Non-native species are one of the important threats to biodiversity. Some non-native fish species pose environmental impacts and are known as invasive species. Rivers of the southern Caspian Sea are home to a vast variety of native or commercial fish species. Non-native species invasiveness risk assessment tools are used to identify the species with high invasive potential risks and are used as a decision–making tool. The main aim of this study is to calibrate and validate the Aquatic Species Invasiveness Screening Kit (AS-ISK) for non-native fish species of rivers in the southern Caspian Sea basin.

AS-ISK was used to assess non-native (NN) fish that may pose a high potential risk of becoming invasive in rivers of the South Caspian Sea. Fifteen NN fish species were assessed, 14 of which are extant and 1 is horizon species in the risk assessment (RA) area. The statistical methods were used to compare the scores obtained by each assessor. The threshold score was calculated using receiver operating characteristic curve analysis. Also, the Köppen-Geiger climate system was used to match the climate between the native range of NN fish species and the risk assessment area.

Risk assessment of NN fish species led to the identification of 73 % of the species as potential invasive species in the RA area. Carassius gibelio and Carassius auratus achieved the highest risk score and Anguilla anguilla obtained the lowest risk score among all NN fish species. There was not a statistically significant difference between assessor-specific mean risk scores. Threshold scores were 9.5 and 11.5 for AS-ISK and Basic Risk Assessment (BRA), respectively. The area under curve was 100%, which shows an excellent output for the efficiency of the AS-ISK in the RA area. Eleven out of the 15 NN fish species were identified as potential invasive species and the rest as non-invasive NN species in the RA area. Confidence factors were different from 73% to 64%. All NN fish species were categorized in three lists i.e., black, grey and white in regard to their risk ranks in order to manage prioritization.

The AS-ISK efficiently identified NN fish species that pose a high risk of being/becoming invasive in rivers in the south Caspian Sea to prioritize them based on their risk rank and to support conservation managers, decision-makers and policymakers in the aquaculture development plans.