Spinner dolphins in Maui County waters

Project Name:
Daytime distribution, behavior and social ecology of spinner dolphins in Maui County waters

Project Dates:
Ongoing

Project Site(s):
Makena Landing, Olowalu, Black Sand Beach and Ka’anapali coastline, Maui

Project Aims:
Determine movement patterns of spinner dolphins in Maui County waters and test for differences in the peak time of resting between locations, and differences in patterns due to presence and absence of boats. The study will also look at the underwater acoustic patterns associated with what is seen at the surface. Using photo-identification, the presence of specific individuals within groups at specific locations will be monitored to determine site-fidelity to specific coastal locations.

Project Justification and Background:
The spinner dolphin (Stenella longirostris) is one of a number of related species in the genus Stenella which also includes a spotted dolphin (S.  attenuata), the striped dolphin (S.  coeruleoalba), and the Clymene dolphin (S.  clymene).  Spinner dolphins range throughout the tropical Pacific, Atlantic, and Indian Oceans.  They are primarily pelagic, but can be found over the continental shelf and around oceanic islands.  In the Pacific, spinners are generally divided into four “races”, including the Costa Rican, Northern whitebelly, Southern whitebelly, and Hawaiian.  The four groups are closely related, differing in relatively minor anatomical features and color patterns, although there are major differences in group dynamics between the pelagic and coastal populations.

The social structure and association patterns of spinner dolphins are extremely fluid, suggesting that animals within the Hawaiian population range widely both around and between islands. However, there is little data available to indicate the extent to which exchange between islands occurs. The seasonal distribution patterns of spinner dolphin groups is generally influenced by the complex interaction between the availability of food, the availability of shallow sandy bottom beaches in the vicinity of the feeding grounds, periodicity (both seasonal and a yearly) and social dynamics (e.g., reproduction, calf rearing).

Spinner dolphins feed at night in waters deeper than 100 feet. They feed on squid which is part of the Deep Scattering Layer (DSL), a suite of marine organisms that stays in the darkness of the deeper waters during the day and rises to the surface at night after sunset. During the daytime spinner dolphins tend to rest or travel at slow speed between areas close to shore. A portion of the spinner dolphin population comes to sandy beaches near shore to rest during the day.  Activity patterns tend to shift from high activity as the dolphins move into a resting area in the morning, to a low activity that peaks around the middle of the day. The period of lowest activity is associated with deep rest when dolphins spend the majority of their time near the bottom and only come to the surface to breathe.

The island of Lanai is connected to the islands of Maui, Molokai and Kahoolawe by a relatively shallow bank less than 300 feet deep. There may be up to three large groups of spinners seen in the four island area. One group is found along the north shore of Molokai, a second along the south shore of Molokai and the third is regularly observed along the south eastern shore of Lanai near Manele bay.  Smaller groups of spinners are sporadically observed along the south coast of Kahoolawe and off the windward coast of Maui.

Pacific Whale Foundation’s efforts on spinner dolphins in Maui County waters started in 1996 under the guidance of Dr. Paul Forestell (in collaboration with Dr. Meagan Jones and Carolyn Hogg) and with the help of Dr. Eric Brown. This research team documented habitat use patterns for spinner dolphins off Lanai.  The current project is a continuation of this effort and is also part of Maria Cristina Ramasco’s specialization thesis at the University of Milano, Italy.  

Project Methodology:
Vessel surveys are undertaken to locate spinner dolphins, monitor their behavior and movement patterns. Individual spinners are photo-identified to monitor  movements and life histories of individual animals. Pacific Whale Foundation holds an historical catalogue of at least 272 individuals seen in Maui County waters since 1996.

Project Permits and/or Collaborators:
NOAA/NMFS LOC No. 13427-02 

Management Outcomes:
TBD

Publications/Presentations:
See  Pacific Whale Foundation Publication/Presentation Summary