Effects of Boat Activity on the Behavior of Bottlenose Dolphins (<I>Tursiops truncatus</I>) in Waters Surrounding Hilton Head Island, South Carolina

Abstract

During the summer of 1998, the effects of boat activity on the behavior of bottlenose dolphins (Tursiops truncatus) were investigated using 52 shore-based surveys along Hilton Head Island, South Carolina. Temporal autocorrelation indicated data collected on most variables should be analyzed in 6-min intervals. Responses to boats were categorized as "no response," "behavioral response," "change in direction of movement," or "change in both behavior and direction." Multiple boats had a greater influence on dolphin behavior and movement than the presence of a single boat. Dolphin-watching boats, motorboats, shrimp boats, and jet skis affected the group size and behavior of dolphin groups. Dolphin groups responded to dolphin-watching boats during 20% of observations, mainly with a change in both behavior and direction of movement. Motorboats caused a response in dolphins during 55% of observations, with a change in behavior or both behavior and direction. Jet skis had a more dramatic effect on dolphin groups, with 56% of groups changing their behavior and 11% changing both their behavior and direction. Shrimp boats always elicited a response. Dolphin groups changed both their behavior, and direction of movement to follow and feed behind these boats. In contrast, ships rarely caused a response, with groups changing their behavior but not their direction in 11% of observations. As the number of boats in the Hilton Head area increased, dolphin groups heightened responses-that is, changed both behavior and direction of movement. These boat-related effects on bottlenose dolphin behavior are considered "harassment" under the U.S. Marine Mammal Protection Act (1972) and should be scrutinized by agencies responsible for public education and enforcement of protective legislation.

The behavior of Sotalia guianensis (Van Bénéden) in Pernambuco coastal waters, Brazil, and a further analysis of its reaction to boat traffic

“…These boats move at constant speeds on predictable courses and do not make attempts to physically contact the animals, but often go through the areas where groups of estuarine dolphins are to be found. For these reasons, the dolphins apparently show a lack of interest in the boats (CONSTANTINE et al 2004, MATTSON et al 2005, STENSLAND & BERGGREN 2007. In addition, particularly with regard to tourist boats with high-powered engines, another probable reason for this is that these animals are not targets for these boats, since they rapidly go through these areas, using them only for transit and not for dolphin-watching activities.…”

Surface patterns of Sotalia guianensis (Cetacea: Delphinidae) in the presence of boats in Port of Malhado, Ilheus, Bahia, Brazil

“…Reactions to different boat types have also been reported for other dolphin species. For Tursiops truncatus, jet skis cause prolonged submersion of individuals, which is associated with the high speed of the boat, undefined motion and the noise produced by the motor (Mattson et al, 2005). The Irrawaddy dolphin (Orcaella brevirostris) decreases its breathing pattern in the presence of motorized canoes (<40 hp), high-speed boats (40-200 hp) and towing ships (>1000 hp) (Kreb & Rahadi, 2004).…”

“…According to Mattson et al (2005), the prolonged time underwater in the presence of outboard motorboats can be a strategy for boat avoidance or even a response to communication difficulty.…”

“…The interaction between cetaceans and boats can cause direct impacts, such as collisions that cause injuries and even death (Laist et al, 2001;Vanderlaan & Taggart, 2007), and indirect effects, such as changes in behavioural patterns (Mattson et al, 2005;Lusseau, 2006). Research conducted on coastal species of Delphinidae has identified behavioural changes in the presence of boats.…”

An Overview of Increasing Incidents of Bottlenose Dolphin Harassment in the Gulf of Mexico and Possible Solutions

“…In addition, activities that bring dolphins into close proximity with fishing gear have the potential to seriously injure or kill the animals through ingestion, entanglement, or even vessel strikes (Zollett and Read, 2006;Read, 2008;Wells et al, 2008;Barco et al, 2010;Powell and Wells, 2011;Stolen et al, 2013). As more people locate to coastal areas and participate in recreational activities, the chances for close encounters increase, making local populations susceptible to disturbance, harassment, or direct attack (Samuels and Bejder, 2004;Mattson et al, 2005;Cunningham-Smith et al, 2006;Zollett and Read, 2006). As a result, it is possible to suggest that a byproduct of dolphin conditioning to human interaction in the region, including activities to swim with or feed these animals, is resulting in closer proximity and access to wild dolphins, exposing them to directed harm and violence (Waring et al, 2015;NOAA, 2016).…”