Physical factors affecting the survival of Tachypleus tridentatus eggs were investigated by translocating their eggs between the high intertidal zone and the low intertidal zone of a known spawning site. The mean egg survival rates per day were highest in the mid intertidal zone (45.1% ± 25.4%) and the lowest in the low intertidal zone (13.3% ± 27.6%). Differences in the elevation, air exposure time, and water content of the spawning ground were significant factors determining the egg survival rates. Excessive or insufficient air exposure time resulted in inadequate water content at higher and lower intertidal zones and could reduce egg survival. On the other hand, moderate saturation and dehydration were repeated with each tidal movement in the mid intertidal zone. This dynamic is considered as one of the crucial factors for the survival of eggs and is considered optimal for spawning. Therefore, the protection of the mid intertidal zone is imperative for maximizing the egg survival rate in Tsuyazaki Cove where almost all suitable nesting sites have disappeared due to coastal development. By protecting these optimal sites for spawning and recovering other optimal sites on suitable beaches, a positive contribution can be made to future management and conservation. The study also suggests that translocating eggs from marginal to optimal spawning sites might be a recovery strategy for this globally endangered species.

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The suitable spawning habitat of Tachypleus tridentatus was estimated and mapped for the first time using scientific modelling in Tsuyazaki, Fukuoka, Japan. A total of 43 nests were found at five sites from 2018 to 2019. Of these 43 nests, the location information of nine nests at one of the sites was used as ‘Training data’ for constructing the models. A series of procedures was employed to determine the relationship between the biological data and their physical parameters to estimate the suitable spawning habitat. First, the contribution rates of the physical parameters (beach elevation, slope and sediment) to nest locations were evaluated. Second, physical parameters that showed significant contribution rates were chosen to estimate suitable spawning habitats. It was found that the beach elevation was the most significant parameter for estimating suitable spawning habitats. Mean high water neap to mean higher high water was estimated as suitable spawning habitat, and 74% of the nests were fitted in an area assessed as suitable. The result was consistent with previous studies. The area of suitable spawning habitat was estimated to be only 476 m2 out of 1943 m2, comprising 24% of the sandy beach in the study site. Therefore, it was concluded that the conservation and restoration of spawning grounds is a high‐priority and urgent issue at the site. It is proposed that scientific modelling of nest/egg occurrence and beach elevation can effectively determine suitable spawning habitats. Thus, it is possible to quickly establish the habitat most suitable for spawning in coastal environments and help plan conservation strategies for this globally endangered species.