MUCRU - Murdoch University Cetacean Research Unit

Hawaii
MUCRU, in collaboration with Dave Johnston (Duke University Marine Lab, North Carolina) and David Lusseau (University of Aberdeen, Scotland) aims to collect baseline data on the local abundance, distribution and behaviour of spinner dolphins (Stenella longirostris) using a suite of modern visual and acoustic techniques in two resting bays (to be determined) in Hawaii. These data will then be used to investigate the effects of human interactions on the spinner dolphins and assess the effectiveness of time area closures as a mitigation approach. Hawaiian spinner dolphins feed on fish, shrimp, and squid that, during the day, remain deep in the ocean but migrate to the surface (upper 200 m) at night. Spinner dolphins hunt cooperatively offshore at night as the deep scattering layer migrates into shallow waters . During the day, spinner dolphins move into shallow coastal waters to rest and socialise. The areas that are used most frequently are wind protected bays, typically < 50 m in depth, and have sandy bottoms (presumably to aid in the detection of predators). As the dolphins begin to rest, aerial behaviours (spins and leaps) subside considerably, the school tightens, the dolphins move slowly back and forth, and they spend most of their time below the surface. Emergent research is showing that cetacean-based tourism (boat-based and swim-with) can cause biologically significant impacts on targeted dolphin communities. In Hawaii, the dolphin-based tourism industry has grown rapidly in the past two decades. Limited quantitative data are currently available to assess potentially biological significant impacts of tourism activities on targeted animals. Hawaiian spinner dolphins have predictable daily movement patterns, foraging offshore at night and returning to inshore sheltered bays to rest during daytime. This set movement pattern may render them particularly vulnerable to disturbance because of their reliance on a limited area of sheltered waters to rest, socialise and avoid predators. Considering the non-sustainable impacts of tourism on dolphins documented in locations of substantially less tourism pressure, similar impacts are likely to be occurring in Hawaii. Specific concerns in regards to human-spinner dolphin interactions include: changes to dolphin behavioural budgets energetic deficits reduced vigilance for predators truncated rest periods alteration of social interactions with conspecifics inadequate recovery from day-time disturbances with a reduction in nocturnal foraging efficiency and displacement of dolphins from prime habitat to less optimal habitat with an increase in predation risk Elsewhere, these effects have lead to long-term consequences for the viability and fitness of individual dolphins and their populations.
Project Aims:
Quantify spinner dolphin daytime habitat use and resting behaviour in a proposed time area closures Determine residency and fidelity patterns of spinner dolphins during day time in near shore habitats in the proposed time area closures and surrounding waters Produce quantitative measures of spinner dolphin exposure to human activities within resting bays Produce quantitative measures of spinner dolphin exposure to human activities in near shore shallow water environments outside resting bays Produce predictive habitat models and individual based models of spinner dolphin behaviour in relation to human interactions
Shark Bay, Western Australia
Tool use in cetaceans has only been documented in one population – the bottlenose dolphin population in Shark Bay, WA. It is believed some of these dolphins use marine sponges as a protective glove for their rostra when they probe for prey in the substrate. All “spongers” are maternally related – they share the same mitochondrial DNA, which is transmitted only through the female line. MUCRU members are collaborating with Dr. Michael Krützen (University of Zürich) and Assoc. Prof. William Sherwin (University of New South Wales) to discern whether tool-use is a genetic trait, governed by ecological factors or transmitted culturally (through social learning by offspring from their mothers). My research explores the possible correlations between locations of the sponge-carrying dolphins and the density and distribution of marine sponges along transect lines in the western gulf of Shark Bay.

Picture of the frame underwater at the stern of the boat. The camera is positioned at the apex of the frame pointing down.	Video recording of the frame descent and a 1 square metre area of two benthic habitats located in the Western Gulf of Shark Bay at samples T119D and T13B. Recorded in 2008 using the integrated data management and video system developed to sample aquatic benthos. Conical sponges can be seen bottom left and middle to top left in sample T13B.