Occupancy of bottlenose dolphins (Tursiops aduncus) in relation to vessel traffic, dredging, and environmental variables within a highly urbanised estuary

• Published in: Hydrobiologia Vol. 792; no. 1; pp. 243 - 263
• Main Authors: Marley, S. A., Salgado Kent, C. P., Erbe, C.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01-05-2017; Springer; Springer Nature B.V
• Subjects: Anthropogenic factors; Aquatic mammals; Biomedical and Life Sciences; Brackish; Coastal development; Coastal zone; Coastal zone management; Dolphins & porpoises; Dolphins (Mammals); Dredging; Ecology; Environmental conditions; Estuaries; Freshwater & Marine Ecology; Habitats; Human influences; Life Sciences; Marine; Marine mammals; Occupancy; Primary Research Paper; Salinity; Tursiops aduncus; Waterfront development; Zoology; ISW, Australia, Western Australia; GAMs; Theodolite tracking; Animal occupancy; Anthropogenic activities
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1007/s10750-016-3061-7

Coastal areas, and thus coastal species, are at increasing risk from human activities. Sections of the coastline of Western Australia are undergoing intense coastal development to fulfil commercial, industrial, and recreational requirements. Multiple populations of bottlenose dolphins (
Tursiops aduncus
) occur around this coastline; however, small community sizes and limited genetic exchange rates make them susceptible to anthropogenic pressure. This study investigated the occupancy of dolphins within the Swan–Canning Rivers, an urbanised estuary, with regard to (1) presence/absence, (2) abundance, and (3) duration in terms of time spent in the area. These response variables were related back to environmental conditions (tidal state, tidal height, salinity, temperature), vessel traffic, and dredging activities using generalised additive modelling. Theodolite tracking data revealed high levels of boat traffic at the two sites considered; however, dolphin occurrence was only negatively affected by vessel density at one of these sites. Dolphin occupancy was also significantly influenced by temperature, with possible seasonal effects. No dolphins were sighted on days when backhoe dredging was present; however, low sample sizes limited statistical interpretation. These results highlight the need to consider context in behavioural response studies, in terms of habitat type studied, explanatory variables considered, and response variables selected.