The Caspian seal (Pusa caspica) from Phocidae family is the only living mammal that exclusively inhabits the landlocked Caspian Sea. This study was first of its kind conducted on the Caspian seals in the southeastern region of the Caspian Sea from 2010 to 2016. Seasonal observations, gender, maturity, biometric parameters and condition index of each observed Caspian seal were studied. Totally 74 live Caspian seals including 42 males and 32 females were observed in this study. The Caspian seals observed in autumn were significantly greater in number than in the other seasons (p<0.05). There was no significant difference between the number of the males and females (p>0.05), however, the number of juvenile seals were significantly more than adults (p<0.05). This study revealed no significant difference in each biometric parameter and condition index in different seasons, and also between female and male Caspian seals (p>0.05). A significant difference was observed between adult and juvenile seals in biometric parameters (p<0.05), however condition index was not significantly different (p>0.05). Since Caspian seals are listed as endangered species in the IUCN Red List, further research is required to understand the status of this population and conserve the only mammals of the Caspian Sea.
