Dolphin sociality, distribution and calving as important behavioural patterns informing management

Abstract

Conservation management typically focuses on protecting wildlife habitat that is linked to important behaviours such as resting, breeding or caring for young. However, development of conservation strategies of social species would benefit from inclusion of social dynamics, particularly for species where social relationships influence fitness measures such as survival and reproduction. We combined the study of dolphin sociality, distribution and calving to identify important behavioural and ecological patterns to inform management. Over 3 consecutive years, 231 boat-based photo-identification surveys were conducted to individually identify adult female bottlenose dolphins over a 120 km 2 area in Bunbury, Western Australia. The density distribution of female dolphins was highest in the inner waters during December-February (austral summer) and March (early autumn), which also coincided in time with the majority of calving. The temporal stability of social bonds between adult females was measured (using lagged association rates) and remained stable over multiple years. A cyclic model best described female-female associations with an annual peak occurring each austral summer (Dec-Jan-Feb). These results informed the implementation of a legislative no-go area and vessel speed restriction areas. In addition to conventional management approaches of protecting important habitat and breeding periods, our measure of dolphin sociality provides a new metric to consider in conservation efforts. We encourage studies on socially complex species to incorporate social dynamics when evaluating possible impacts of anthropogenic activities. 462

Dolphin Prey Availability and Calorific Value in an Estuarine and Coastal Environment

“…In the summer months, the number of prey, as well as the total and PDP biomass caught by the seine and gillnet was highest in the Estuary, which does not match the density of adult female dolphin sightings from March 2007 to February 2010, which were highest in the Estuary in the winter (Smith et al, 2016). The mean number of PDP species caught per trap was highest in the Ocean region in the summer months, which was not sampled using the seine or the gillnet.…”

“…In winter months, the gillnet, which sampled larger fish than the seine, caught the highest PDP biomass in the Estuary, which corresponds to the time of higher density of female and calf dolphin sightings in the Estuary (Smith et al, 2016). The seine net had higher catch rates in the Bay in the winter.…”

“…The abundance of dolphins fluctuates seasonally, with approximately double the population size in the summer vs. the winter months (Smith et al, 2013;Sprogis et al, 2016a). The seasonal high in abundance coincides with the peak in the breeding and calving season, in late summer/early autumn (Smith et al, 2016).…”

“…We hypothesized that dolphin prey availability in different regions of the Bunbury coastal waters would be greater in the summer months when dolphin abundance is highest, and would be greater in the Bay during the summer, as adult female dolphin sightings are more concentrated in the Bay during summer months (Smith et al, 2016). We also hypothesized that energetically rich prey would be present yearround to support the high energetic requirements of pregnant and lactating females that appear to have high affinity to the area.…”

Best Practice Framework and Principles for Monitoring the Effect of Coastal Development on Marine Mammals

“…Is the site appropriate for development? Marine mammal species are diverse and some species are far more vulnerable to adverse impacts from particular activities due to their life history parameters, population size, restricted usage areas, site fidelity and/or social system (Hawkins and Gartside, 2008;Wade et al, 2012;Cagnazzi et al, 2013b;Brakes and Dall, 2016;Smith et al, 2016). For example, a small localized population of coastal dolphins that uses habitats in the vicinity of an impact zone to perform critical tasks (e.g., feeding and reproduction) on a daily basis is likely to be more susceptible to associated risks from the activity, such as the bioaccumulation of pollutants, or repeated disturbance to important behaviors, than a migratory species that has transitory exposure to the pollutant or disturbance factor.…”