Bottlenose dolphins (Tursiops truncatus) are migratory marine mammals that live in both open-ocean and coastal habitats. Although widely studied, little is known about their occurrence patterns in the highly urbanized Chesapeake Bay, U.S.A. The goal of this study was to establish the spatial and temporal distribution of bottlenose dolphins throughout this large estuarine system and use statistical modeling techniques to determine how their distribution relates to environmental factors. Three years (2017-2019) of observational dolphin sighting reports from a citizen-science database, Chesapeake DolphinWatch, were used to determine relative occurrence throughout the estuary. The dolphins had a distinct temporal pattern, most commonly sighted during summer months with a peak in July. This pattern of observed occurrence was confirmed with passive acoustic detections of dolphin echolocation clicks. Using a Generalized Additive Model (GAM), dolphin presence was found to be significantly correlated to spring tidal phase, warm water temperature, and salinity ranging from 6 – 22 PPT. Further, we were able to use these GAMs with a test dataset to predict species occurrence in the Bay, which were statistically correlated to the actual number of dolphin sighting reports during that time. These models can be implemented as a predictive tool for species occurrence and help to inform management of this protected species within the Chesapeake Bay.

This dataset was collected by a citizen science initiative named Chesapeake DolphinWatch, which is available as a web-based application or a phone application for iPhones/Androids. The daily dolphin sighting information was summed to weekly dolphin sightings. All environmental data, collected from the Maryland Department of Natural Resources (http://eyesonthebay.dnr.maryland.gov), the National Oceanic and Atmospheric Admistration (https://buoybay.noaa.gov), the Chesapeake Bay Program (http://data.chesapeakebay.net/WaterQuality), and the Astronomical Applications Department of the US Naval Observatory (https://www.usno.navy.mil/USNO/astronomical-applications). These data, too, were summed to represent weekly values. 

Additional information regarding Chesapeake DolphinWatch can be found here: https://www.umces.edu/dolphinwatch, https://chesapeakedolphinwatch.org.