Changes in surfacing patterns of bottlenose dolphins in response to boat traffic

TitleChanges in surfacing patterns of bottlenose dolphins in response to boat traffic
Publication TypeJournal Article
Year of Publication1996
AuthorsJanik, Vincent M., and Thompson Paul M.
JournalMarine Mammal Science
EndNote Rec Number5117

Recent growth in commercial whale and dolphin watching has raised the question of how cetaceans are affected by boat traffic. Many studies in this field looked at effects on baleen whales (review in Richardson et al. 1995), while only a few, e.g., Au and Perryman (l982), Kruse (1991) and Polacheck and Thorpe (1990) have studied influences on smaller odontocetes. The dominant behavioural reactions of cetaceans reported in these studies were an increase in swimming speed, spatial avoidance, and changes in diving behaviour. All these are short-term reactions which may disrupt the ongoing activities of the animals. Such disruptions could cause longer-term changes in the behaviour and status of a population through avoidance of certain areas or an increase in mortality (Thompson 1992, Richardson et al. 1995). Assessments of the potential impact of boat traffic therefore require a fuller understanding, first, of the nature of any short-term changes in behaviour and, second, of the longer-term consequences of any reactions. The aim of this study was to quantify the behavioural reactions of bottlenose dolphins (Tursiops truncatus) to boat traffic in the Moray Firth, N.E. Scotland. Bottlenose dolphins have been recorded in the Moray Firth since at least the early 1970s (Evans 1980), and previous studies indicated that dolphins were often observed in the narrow channels which link the inner firths (Hammond and Thompson 1991). This study was carried out overlooking the Kessock channel, which connects the Moray and the Beauly Firths (Fig. 1). Water depth increases gradually from 6 to 38 m from east to west in the area. Because it is a relatively narrow channel tidal, currents are strong. All observations have been made at rising tide. The area is exposed to frequent boat traffic because it connects the Caledonian Canal with the North Sea. Commercial dolphin watching trips also started operating in this area in 1994.