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 four 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.
- 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
This study 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 four resting bays along the Island of Hawaii, Kauhako Bay, Honaunau Bay, Kealakekua Bay and Makako Bay. 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.
Photographs of spinner dolphins will be obtained with digital SLR cameras equipped with zoom lenses from small boats. Photographs will be analyzed for individual distinctiveness based on the patterns of nicks and notches in the dorsal fins and flukes and, to a lesser extent, by scar or colour patterns on the bodies. Photographs of animals will be compared between encounters and between years to look for matches.L003 New individuals will be entered into the catalogue under one of two conditions; the individual is sighted in more than one encounter and the overall quality of the photograph is at least average, or the individual is sighted once and the overall quality of the photograph is excellent. Photo ID data will be used to develop an initial discovery curve for encountered animals and will subsequently included in a mark/recapture analysis.
Boat-Based Surveys, Behavioural Sampling and Group Focal Follows
Surveys for spinner dolphins will be conducted using small boats with outboard engines. Two to 5 observers on the small boat will be scanning for dolphins constant on pre-determined track lines in the study area. When dolphins are detected, the boat will break from track line to approach the group of dolphins for photo ID purposes and behavioural sampling. Dolphins will be approached slowly, with no changes in engine RPMs on rapid accelerations or decelerations. We will attempt to photograph all dolphins within groups encountered, to provide further details on group size and the marked to unmarked ratios for this species. Both individuals and groups will be chosen as the focal unit to follow, and the boat will parallel the movements of the focal unit and collect information on the focal unit’s behaviour and interactions with others.
Bottom Mounted Acoustic Loggers
Recordings of the acoustic behaviour of spinner dolphins in resting areas will be collected using smallLogger bottom-mounted archival DSG hydrophone packages. These devices will be deployed in spinner resting habitats and recovered and redeployed as required by battery life and storage allows. Recorders will be deployed using weights as ballast. Acoustic data collected during the proposed work will provide insight into local vocalization rates (both whistles and echolocation clicks) and provide a more detailed time series of spinner acoustic behaviour before and after the closure is implemented.
Land-Based Theodolite Tracking
Where possible, the movements and behaviour of spinner dolphins and boats will be studied from local cliff tops using a digital theodolite. Digital theodolites convert angles of declination and azimuth to xy coordinates using standard trigonometric functions. Theodolite surveys have been used extensively to study spinner dolphins in Hawaii, and these previous studies may provide useful comparisons, although we will focus on simplified behavioural descriptions as response variables. For example, theodolite surveys will provide detailed information on the habitat use of groups of resting and non-resting spinner dolphins, including geographic location (for habitat modelling), movement patterns and closest observed approaches in relation to human presence in the closure area (for individual-based modelling analyses).