Bottlenose Dolphin Responses to Boat Traffic Affected by Boat Characteristics and Degree of Compliance to Code of Conduct

Abstract

Levels of boat traffic in coastal seas have been steadily increasing in many parts of the world, introducing pressures on marine wildlife through disturbance. The appropriate management of human activities is important not only to preserve wildlife, but also for the local communities that depend on ecotourism for employment and their economy. This study presents further insight into bottlenose dolphin (Tursiops truncatus) responses to boats in New Quay Bay (West Wales) within the Cardigan Bay Special Area of Conservation. This region is heavily dependent on wildlife tourism, and marine traffic is regulated through a long-standing Code of Conduct. Based on a long-term dataset spanning the months of April to October and the years 2010–2018, the study found that compliance to a code of human behaviour increased dolphin positive responses towards boats. Dolphin responses to individual named boats and to different boat types were examined in greater detail. Speed boats, small motorboats, and kayaks were found to break the code most often, resulting in higher rates of negative response by dolphins. Visitor passenger boats formed the majority of boat traffic in the area, and showed greater compliance than other general recreational crafts. Suggestions are made for the better protection of the coastal dolphin population, as well as the role that citizen science can play to help achieve this goal through working directly with wildlife trip boats and the recruitment of local observers.

Vessels Disturb Bottlenose Dolphin Behavior and Movement in an Active Ship Channel

“…A multitude of anthropogenic activities in coastal environments (e.g., dredging, commercial fishing, recreational boating, tourism, commercial shipping) can alter marine mammal behavior and movement patterns [1][2][3]. Vessel activity poses various risks to marine mammals including short-term behavioral disruptions that reduce foraging or resting, long-term shifts in behavior that change social structure and habitat use, and collisions resulting in physical injury or death [4][5][6]. Dredging operations, tourism and recreational vessels, and the presence of many large vessels in major shipping ports and marinas contribute to increased vessel traffic and noise pollution that can change dolphin distribution and behavioral patterns [7][8][9].…”

“…Knowledge of how vessel activity impacts marine mammals is crucial as human populations continue to increase along the coast and modify marine environments [10][11][12]. Common bottlenose dolphins (Tursiops truncatus; henceforth "bottlenose dolphins") demonstrating high site fidelity to a coastal area may alter their behavior or movement patterns when vessels are present (e.g., approach or avoid a vessel) [3,4,6,[12][13][14][15].…”

“…Bottlenose dolphin behavior in the Galveston-Bolivar ferry lane shifted from foraging to predominantly traveling when medium-sized ferries were nearby [16]. Tourism and small recreational vessels that did not adhere to regulations altered dolphin behavior and habitat use, indicating a need for proper vessel operation around bottlenose dolphins [6,16]. Dolphin-watching tours may repeatedly seek out dolphin groups in coastal areas for lengthy close-up encounters.…”

Raise your pitch! Changes in the acoustic emissions of resident bottlenose dolphins in the proximity of vessels

“…The underwater soundscape of the oceans has changed rapidly and significantly due to increased noise generated directly or as a by-product of human activity (Duarte et al, 2021). Shipping is the main source of underwater anthropogenic noise and contributes to increased ambient noise especially in coastal areas (Duarte et al, 2021;Jensen et al, 2009;Koroza & Evans, 2022).…”

“…Vessel noise often overlaps the frequency bands dolphins use for echolocation and communication, potentially masking important acoustic information in their habitat (Guerra et al, 2014; Jensen et al, 2009). In coastal areas, some noise sources play a predominant role, and smaller vessels (e.g., dolphin watching vessels, fishing boats, ferries, and motorized vessels) that have a closer interaction with sensitive marine animals may be an important source of disturbance for local and resident populations (Jensen et al, 2009; Koroza & Evans, 2022; Wisniewska et al, 2018). The Sado estuary (Portugal) is an important habitat for a small resident population of about 27 common bottlenose dolphins ( Tursiops truncatus ; Luís et al, 2016a,b) that overlaps with various human activities and high intensity maritime traffic.…”