A brief study on the true freshwater crab Potamon ibericum (Bieberstein, 1808) absence downstream of Kasilian River, Mazandaran, Iran

Potamon ibericum is one of the true freshwater crab species in Iran, which has been endangered in recent years due to climate change and human activities. This freshwater crab is mostly found in the rivers located in the Hyrcanian forests of northern Iran, due to their high food diversity and suitable temperature. In this research, we focused on the absence of this species downstream of the Kesilian River, and we achieved important results. Sampling was conducted at eight different points along the river in April, June, July, September, November, and December to study the effects of temperature and environmental conditions on P. ibericum distribution. Our study revealed that the reasons for its absence are related to numerous human and non-human factors. The human factors include poultry farming; heavy machinery passing through the river to transport logs, sand, and rocks, which often result in oil and fuel leakage; and the expansion of agricultural and horticultural activities. The non-human factors include the presence of invasive species such as hooded crows and temperature changes, where the highest population of live crabs was observed during the warmer months, while the lowest population was recorded during colder temperatures. These findings emphasize the critical role of temperature conditions and human activities in the habitat distribution of P. ibericum, which has significant implications for further studies and conservation measures. Our goal is to help formulate strong strategies that ensure the sustainable presence and flourishing of P. ibericum in its native environment and encourage other researchers to investigate more deeply in this field.