University of Tehran Journal of Natural Environment 2008-7764 75 4 2022 10 23 Investigating the presence and diet of otter (Lutra lutra) in the estuary region of eastern rivers of Guilan province: Polrood, Khoshkrod and Acharod Investigating the presence and diet of otter (Lutra lutra) in the estuary region of eastern rivers of Guilan province: Polrood, Khoshkrod and Acharod 716 732 88279 10.22059/jne.2022.341273.2420 FA Saeid Eshagh Nimvari Department of Environment , Faculty of Natural Resources, University of Guilan, Sowmeh Sara, Iran Saeid Naderi Department of Environment , Faculty of Natural Resources, University of Guilan, Sowmeh Sara, Iran Alireza Mirzajani Inland Water Aquaculture Research Center,, Iranian Fisheries Science Research, Institute, Agricultural Research Education and Extension Organization (AREEO), Bandar Anzali,, Iran Journal Article 2022 04 07 The Eurasian otter (<em>Lutra lutra</em>) as one of the mammals of the inland waters of Iran is at the top of the food pyramid and encounter to endanger of extinction. The diet studies are critical to understanding the ecology of wildlife and preserving their populations. The objectives of this study were the presence and diet of otter in estuary region of Acharod, Khoshkrod and Polrood rivers, in the east of Guilan province, and also the study of the level of dependency of this species on fish species of the Caspian Sea. The length of the last five kilometers of each river, as three sections with an approximate length of 1700 meters, was examined in terms of distance or proximity to the sea. The results showed that of the five km length studied of the rivers, the Eurasian Otter was present up to 4/3 km of the estuary. In total, 511 presence indices with specific seasonal changes were observed in each of the river sections. The highest index was observed in the autumn season and the lowest in the summer season. Based on the analysis and investigation of spraints, 955 prey items including fishes, crustaceans, snakes, frogs, birds and insects were observed. The highest feeding index (FI) in three studied rivers was for fish and the lowest FI was for insects. Also, the seasonal changes in food items between sections were observed. So that in the two seasons of autumn and winter in all three sections of the rivers, the highest FI was for fish. In the spring and autumn, the feeding index of the fed fish was mainly related to river fish and common river-sea fish. In summer and winter, the percentage of sea fish was higher than in spring and autumn. The feeding index of non-fish items has also increased in the summer compared to other seasons. The Eurasian otter (<em>Lutra lutra</em>) as one of the mammals of the inland waters of Iran is at the top of the food pyramid and encounter to endanger of extinction. The diet studies are critical to understanding the ecology of wildlife and preserving their populations. The objectives of this study were the presence and diet of otter in estuary region of Acharod, Khoshkrod and Polrood rivers, in the east of Guilan province, and also the study of the level of dependency of this species on fish species of the Caspian Sea. The length of the last five kilometers of each river, as three sections with an approximate length of 1700 meters, was examined in terms of distance or proximity to the sea. The results showed that of the five km length studied of the rivers, the Eurasian Otter was present up to 4/3 km of the estuary. In total, 511 presence indices with specific seasonal changes were observed in each of the river sections. The highest index was observed in the autumn season and the lowest in the summer season. Based on the analysis and investigation of spraints, 955 prey items including fishes, crustaceans, snakes, frogs, birds and insects were observed. The highest feeding index (FI) in three studied rivers was for fish and the lowest FI was for insects. Also, the seasonal changes in food items between sections were observed. So that in the two seasons of autumn and winter in all three sections of the rivers, the highest FI was for fish. In the spring and autumn, the feeding index of the fed fish was mainly related to river fish and common river-sea fish. In summer and winter, the percentage of sea fish was higher than in spring and autumn. The feeding index of non-fish items has also increased in the summer compared to other seasons. https://jne.ut.ac.ir/article_88279_56f092e77ce57008893220ffc41b17a3.pdf