Scientific research on spinner dolphins (Stenella longirostris) began in the late 1960’s when Dr. Ken Norris went to Kealakekua Bay, on the Island of Hawai’i, to ascertain whether that would be a good location to study dolphins.  Since then the Island of Hawai‘i has continued to be the center for spinner dolphin research.  There are many aspects of the research that merits mentioning.  The following are the areas that will be addressed here.

• History of the Big Island Spinner Dolphin Research

• Social Organization

• Social Behavior

• Acoustics

• Underwater Viewing Vessels

A.  History of the Big Island Spinner Dolphin Research Program

The research on spinner dolphins, off the Island of Hawai‘i (the Big Island), represents the longest running study of spinner dolphins in the world and one of the longest running studies of any dolphin species, spanning over 30 years.  The research has been carried out in four separate studies, involving Ken Norris and several of his colleagues, postdoctoral and graduate students.

1968 - 1974 — The Initial Study

Dr. Ken Norris initiated the spinner dolphin research, when he found them residing in Kealakekua Bay on the Big Island on a regular basis.  Ken’s early work focused on Kealakekua Bay and involved one of his students, Tom Dohl.  This initial work featured Ken’s extraordinary skills as a naturalist, where he was able to describe the basic framework of spinner dolphin biology.  They observed the dolphins from shore, and made aerial surveys around the Big Island and throughout the Hawaiian Island chain.  Several important discoveries came from this work.  They found that spinners rest near-shore during the day and travel offshore in the afternoon to feed at night on the deep scattering layer (see side bar), as it moves closer to the surface, after dark.  They discovered that, in Hawai‘i, spinners tend to rest in bays with a sandy bottom and described many details of the circadian (24-hour) activity cycle that spinners go through, as well as, the various aerial behaviors that these acrobatic dolphins perform.  Ken developed the first underwater viewing vessel, the “Semi-Submersible Seasick Machine” to study dolphins underwater in the wild.  This vessel was used to study the spinners in Kealakekua Bay.  Ken Norris describes this pioneering research in “The Porpoise Watcher”.

1979 - 1981 — The Hana Nai‘a Project

A group of Ken’s postdoctoral, graduate and undergraduate students returned to the Big Island to continue the research.  This group included Bernd Würsig Randy Wells, Shannon Brownlee, Christine Johnson and others, many of which that have made major contributions in marine mammal science.  This project focused on quantifying many of the features of spinner dolphin biology that had been described in the first study.  The project was again based in Kealakekua-bay.  The dolphins were tracked from a shore station with a theodolite, photographed from boats for individual identification purposes, and radio-tracked at night to follow their movement offshore to and in their feeding areas and along shore.  Their sounds were recorded and their behaviors were observed underwater using the 2^nd generation underwater viewing vessel, the “Maka Ala”.  They also did aerial surveys and observed a captive colony of spinner dolphins at Sealife Park, on O‘ahu.  Much of the information from this work can be found in two books, a scientific book, “The Hawaiian Spinner Dolphin”, and a popular book by Ken Norris, “The Life and Times of the Hawaiian spinner dolphin”.  The latter won the Burrough’s award for best Natural History writing in 1992.

This study identified 224 individual spinner dolphins and estimated between 1,000 and 2,000 dolphins around the island of Hawai‘i.  It described a fission-fusion society where schools changed composition on a daily basis.  However, some animals were found to associate tightly.  Some individuals were observed to move from one side of the island to the other in a matter of days

1989 - Present — The Kula Nai‘a Project

After a brief project on the Island of Lana‘i in 1988, we (then Ania Driscoll and Jan Östman) came to the Island of Hawai‘i in 1989, to continue the research on the Big Island spinner dolphin population.  We were both graduate students of Ken’s, and as such had a great base for our project from all the excellent work that had already been done by the researchers before us.  We continued the emphasis on quantification and focused our observations on the social organization, social behavior and vocal communication of the spinner dolphins.  We also made underwater observations an important part of the research, using the 3^rd generation underwater viewing vessel, “Smygtittar’n”.  Working out of Honokohau harbor, our research was based North of Kealakekua Bay, mainly from Noio Point to Mano Pt.  However, we also went farther South, to Kealakekua Bay and Kauhako Bay on many occasions.

We identified 677 individual spinners and estimated a total population size of 2,334 spinner dolphins around the Big Island.  The underwater viewing vessel made it possible to sex 68 of the identified spinner dolphins, allowing us to compare the association patterns of males and females.  It also made it possible to collect 50 hours of focal animal follows, where we videotaped the social interactions between the focal animal and other spinners for up to 45 minutes.  Using DAT (Digital Audio Tape) recorders we recorded their sounds, categorized their whistles and studied the whistle choruses they make at certain times of the day.

B.  Social Organization

The social organization of Hawaiian spinner dolphins differ from that of bottlenose dolphins, the most extensively studied dolphin species.  Spinner dolphins are found in much larger schools, often numbering 40 to 80 animals.  Off the Kona Coast you can often see these schools moving along the shore divided into subgroups of roughly 20-25 individuals each, spaced about 50 meters apart.  Thus a school with 2 subgroups often have around 40-50 individuals, while a school with 3 subgroups may have about 60-75.  To study these groups further you need to be able to identify individual animals.

1.  Photographic methods for identifying individuals

To study the social structure of any species you need to identify individuals and observe their patterns of association both in the short-term and in the long-term.  Biologists have learned to identify individuals of many mammalian species by some variation in outward appearance, such as the pattern of whiskers on lions, the shape of a certain color patch on the necks of giraffes, or the coloration and other markings on the tail flukes of humpback whales.  For most species of wild dolphins, the patterns of nicks and notches on the leading and trailing edges of the dorsal fin is used, making it possible to identify individuals by their dorsal fin silhouette.  (Trainers of captive dolphins learn to identify their animals by their faces).  Since many of these patterns are too subtle for a definitive identification in the field you need to photograph the dorsal fins of all individuals to get the complete school composition.  Unfortunately, however, many spinner dolphin fins are clean, i.e. they do not have any identifying markings.  This is especially the case for younger animals and, we suspect, for females.

To get a quantitative measure of the social affiliation patterns among the spinners, we calculated a Coefficient of Association (CoA) for each pair of the 677 individuals we have identified to date.  A CoA of ‘100’ means that the two individuals were ALWAYS seen together in the same school, while a CoA of ‘0’ means that the two individuals were NEVER seen in the same school

We found that female-female associations among the spinners were similar to those seen in bottlenose dolphins and lions, with an average female-female pair spending about 40% of their time in the same school.  The male spinner dolphins, however, formed more extensive networks of associations and often formed tight core groups of 6 or more males, spending 60% or more of their time together.  Female-male association were also very high, falling in between male-male and female-female associations, and much higher than comparable associations among studied bottlenose dolphins.

C.  Social Behavior

The social interactions among spinner dolphins are very unusual for a mammal.  In most mammalian species, the females are very important resources for the males, since they carry the offspring in the womb for an extended period of time and then nurse the offspring after it is born, thus putting a lot of energy into the offspring.  As a result male mammals tend to compete with each other for access to females.  They then engage in a consortship with the female to convince her that he is the one that should be the father of her offspring.  Among mammals, then the emphasis is often on male-male competition and female choice.

Our research indicates a very different pattern for spinner dolphins.  We need to collect more data to confirm these patterns statistically, but the emerging pattern is consistent and intriguing.  We have seen females compete over access to males on several occasions, while male competition over females appears to be muted.  Females have, furthermore been seen to solicit males, while males have not been seen to overtly solicit females.  Female spinners often initiate social and sexual interactions with males by rubbing on the males, and also solicited their attention in other ways.

D.  Acoustics

1.  Types of sounds spinner dolphins make

Spinner dolphins, like most other dolphins, make three types of sound, burst-pulse sounds, clicks, and whistles.  Burst-pulse sounds are the basic types of sound you normally associate with mammals, like barks, grunts, and moos.  These sounds have not been much studied, since they are hard to describe and to quantify.  Clicks are extremely short-duration sounds containing a very wide range of frequencies.  Individual clicks sounds like clapping you hands or tapping concrete with a hard object.  A series of clicks may sound more like a rusty hinge when you slowly open a door — think of your favorite scary movie.  Whistles are long duration sounds with a very narrow frequency range.  Dolphin whistles sounds just like human whistles, except that dolphins are exceedingly better at changing the frequency (pitch) and have a much wider frequency range.

2.  Studying spinner dolphin whistles

To study spinner dolphin whistles can be a very tedious endeavor.  When you put your hydrophone (underwater microphone) in the water your may record a cacophony of sounds, where you may hear all three types of sounds simultaneously.  (Ken Norris called this the Yugoslavian news report.)  Then imagine trying to tease these sounds apart, when you know that you have 60-80 animals around you.  At other times, however, you may only record one whistle at the time from the same school.

We categorized whistle sequences in three categories, repeated contours (the same contour is repeated several times, low chorus (2-4 overlapping whistles) and high chorus (5 or more overlapping contours).  The low and high chorus became more frequent during the afternoons, with the high chorus being especially prevalent in the hour before sunset.

We also found that spinner dolphin whistles has both strong individual identity and behavior state characteristics.  We suggest that whistle communication functions at three levels: to exchange information between individuals, to coordinate subgroups, and to signal or trace transitions of behavior states within an entire school.

E.  Underwater viewing Vessels

The underwater viewing vessel, Smygtittar’n, Swedish for “The Tip-Toeing Looker”, or “The Peeping Tom” was a long time in the making.  It was the third generation underwater viewing vessel designed by Ken Norris.  It began with one of Ken’s crazy ideas.  He wanted to study dolphins underwater in the wild, something that now seems to be an obvious, although difficult thing to try.  However, although Ken had grand ideas, he was limited financially (a problem we are still struggling with), so he had to put together something on the cheap.  His first contraption, the “Semi-Submersible Seasick Machine” (SSSM), was an airplane fuel tank, with a welded-on inverted tower.  This vessel could be towed by another vessel or, later move under it’s own power.  However, in field tests during the initial study (1968-74) the usefulness of the SSSM was found to be very limited, something that Ken describes in vivid detail in his book “The Porpoise Watcher”.

When he later came back to Kealakekua bay for the Hana Nai‘a project, he brought the second generation underwater viewing vessel, the “Maka Ala”, a vessel that Ken describes as a 17 foot skiff with a coffin attached to its bottom. This was not a very seaworthy platform and it ended up sinking in a rainstorm.  It was also of limited use, even though, just as its predecessor, it gave valuable glimpses into the lives of the dolphins.  For more descriptions of the pros and cons of this vessel, see ”Dolphin Days”.

Smygtittar’n had it’s own history.  It was initially donated to the University of California Santa Cruz and sat at the Long Marine Lab. for years, with weeds growing in it.  Initially it was a 19’ long by 6’ wide Coast Guard Crash boat, with some big holes and rusty fasteners in it’s 1940’s fiberglass cathedral hull.  During it’s development into a research tool, it grew to be 24’ by 8’.  We had a 40” hole drilled through its center and a well built up around it.  An A-frame was built to straddle the well and a three-foot-diameter, ten foot tall aluminum observation chamber was hung in the A-frame via cable.  This allowed us to winch up the chamber while it was not in use and to lower it down some six feet, with he help of 1.4 tons (3,000 lbs.) of lead, and lock it in place with bolts into the observation position.  An observer could then climb down into the chamber and record the dolphins’ interactions in front of the underwater viewing windows with a still-photo or video camera.  When it was time to go back to the harbor, we could pull the chamber back up and turn the bottom of the hull into a regular shape again, although the boat again felt the weight of the ballast.

The total displacement of this 24-foot vessel, 4.5 tons (10,000 lbs.), gave it a tendency to go through the waves when the chamber was up, rather than over them like a regular vessel.  As a result we only stayed within swimming distance from shore, less than a mile out, at all times limiting our observation sessions to the mornings when the dolphins were close to shore.  When the chamber was down, on the other hand, the vessel lost about half of its weight, due to the buoyancy of the air in the observation chamber.  However, it gained a six-foot keel with a three-foot diameter.  It thus, turned into a slow but amazingly maneuverable vessel.  It could literary turn on a dime, since the chamber when down served as a pivot point, allowing us to maneuver around coral heads if necessary.  (The development of Smygtittar’n was made possible by funding and help from several sources, including NSF, Waikoloa Marine Life Fund, and Hoogan Boatworks in Kailua-Kona.)