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 estuary of the Chesapeake Bay, USA. 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 (April-October 2017–2019) of dolphin sighting reports from a citizen-science database, Chesapeake DolphinWatch, were analyzed. The dolphins had a distinct temporal pattern, most commonly sighted during summer months, peaking in July. This pattern of observed occurrence was confirmed with systematic, passive acoustic detections of dolphin echolocation clicks from local hydrophones. Using spatially-exclusive Generalized Additive Models (GAM), dolphin presence was found to be significantly correlated to spring tidal phase, warm water temperature (24–30°C), and salinities ranging from 6–22 PPT. We were also able to use these GAMs to predict dolphin occurrence in the Bay. These predictions were statistically correlated to the actual number of dolphin sighting reported to Chesapeake DolphinWatch during that time. These models for dolphin presence can be implemented as a predictive tool for species occurrence and inform management of this protected species within the Chesapeake Bay.
As the understanding of the possible impacts of anthropogenic underwater sound has increased, so have efforts been designed to reduce the effects to marine species and habitats. Consequently, over the last decade, a large number of new policies, regulations, and joint efforts to reduce anthropogenic sound and mitigate affects to aquatic life have been introduced internationally. The United States, Canada, the EU, and many regional and multinational organizations have implemented regulations governing underwater anthropogenic sound. While habitat-centric policies have been developed internationally, difficulty in implementing these highlights the need for additional research including efforts to monitor over longer temporal scales, assess impacts to estuarine and freshwater environments, obtain baseline data where possible, and better understand impacts of chronic noise on individual fitness and population health. This paper reviews the developments in policy focused on reducing the impacts of anthropogenic impacts on aquatic habitats and makes recommendations on research efforts required to manage the impact of underwater anthropogenic sound on habitats.
The effects of underwater sound on fishes are of increasing concern for managers, regulators, and researchers. While there has been work which demonstrated changes in behavior, these studies have generally evaluated of immediate or near-term responses. Understanding acute changes in behavior is necessary, but questions about long-term responses to underwater sound, including any habituation and the relative influence of environmental conditions versus anthropogenic sound must also be investigated. To further elucidate potential response to chronic underwater vessel generated sound, passive acoustic monitoring was used to measure the response of vocalizing oyster toadfish (Opsanus tau) to vessel sounds within the Chesapeake Bay. An automatic detector was configured which allowed for counting of vessel passages and toadfish vocalizations. The response of vocalizing toadfish individual vessel movement was then evaluated. Next the response of toadfish to elevated sound levels across a 30-day period was measured and compared to short-term response. In addition, the influence of environmental variables and contrasted effects of these on the effects of increased anthropogenic sound was investigated.
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