Design-based and model-based estimations of distribution and abundance of dolphin populations in Gulf of Corinth, Hellas

In recent years a major scientific effort has been focused on the protection of marine mammals. Gulf of Corinth is part of the Natura 2000 network (GR2530007) since 2016, with Special Areas of Conservation and constitutes an important habitat for striped dolphin (Stenella coeruleoalba), bottlenose dolphin (Tursiops truncatus) and short-beaked common dolphin (Delphinus delphis). Dedicated shipboard transect line surveys were designed and based in Conventional Distance Sampling and were implemented seasonally during 2018-2019, using passive acoustic and visual techniques, combined with related data derived from 2005-2006 field surveys. Estimation of distribution and abundance of dolphins’ population with a design-based approach using factors such as weather conditions and cluster sizes surprisingly revealed the total absence of Delphinus delphis from the studied area. Density Surface Models (DSM) were used to model these adjusted counts based on a formula involving environmental covariates (depth, surface temperature, chlorophyll-a), in order to investigate the response of populations to biotic and abiotic covariates. Model-based approach for mapping the spatial distribution of animal species clusters can be a useful management tool in establishing protected areas, as well as in communicating monitoring data with non-experts.