Hawaiian spinner dolphins (Stenella longirostris) feed nocturnally and rest in protected bays and coves during the day.  The duration of the stay varies with bay, school size and season.  Generally, a spinner dolphin school arrives in a resting area in the early to mid-morning and stays until mid-afternoon.  While there, the school spends most, if not all, of its time within a core resting area that generally occupies only a small part of the bay or cove.

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Early studies of spinner dolphins described dispersed schools arriving in a resting area, often divided into several subgroups and “with considerable aerial behavior”.  Once in the bay, the school gradually subsided into a resting mode, with individuals swimming quietly and close together, without any splashing or other aerial behavior. The school also generally began to swim slowly back and forth in the core resting area in a rather predictable pattern, turning at each end to swim back the way it came.  Once in deep rest, the entire school tended to spend 3-4 minutes below the surface, mostly swimming slowly just over the bottom in what was termed the ‘carpet formation’ (see image above).  In between dives, the entire school usually spent 20-30 seconds at the surface when all individuals would take several breaths before descending.

The swim-with-wild-dolphin tours began in Kealakekua Bay on the Island of Hawaiʻi in the late 1980’s when a newly established resident brought paying customers to swim with the dolphins. It spread out of that bay and along the Kona Coast in the early 1990’s, when some dive companies and newly established swim-with-tours began dropping customers on the dolphins. By the late 1990’s the situation had grown worse, as more and more swim-with tours established themselves. The result was devastating to the spinners, their rest continuously disturbed and rarely allowed to descend into their traditional resting pattern - synchronized 3-4 minute-long dives and no aerial behavior. The dolphins shifted their behavior, spending time resting in less optimal locations along the Kona Coast, where they had never been seen to rest before. The occupancy rate for Kealakekua bay, percentage of days spent in the bay, dropped from the 70-80% it had in the 1970’s down to 40%, or less.

The consequences of this continuous disturbance is not fully appreciated. Beyond the immediate stress imposed by the swimmers and vessels in the resting area during the dolphins’ resting period, the lack of rest during the day is bound to have an impact on  all other aspects of their lives, such as their ability to perform their highly coordinated foraging behavior at night.

The spinner dolphins used Kealakekua Bay as a resting area. When they entered the bay they immediately headed for an area right under the cliffs, described as their core resting area back in the 1970's, where they spent most of their time. Before the dolphins entered the bay there were few, if any people in this area.

However, as soon as the dolphins showed up, both swimmers (in snorkeling gear), kayakers and motorboats entered the Core Resting Area in large numbers.

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Swimmers and/or Kayakers were in the Core Resting Area with the dolphins throughout most of the day.

The swimmers and kayakers clearly pursued the dolphins and tried to interact with them, while the motor boats stayed a little farther away.

The Dolphins reacted to the approach of people by increasing their activity level, increasing the number of high energy, acrobatic and fast-swim, aerial behavior.  An overwhelming majority of these behaviors were recorded when people were within 91m (100 yards) of the dolphins. This pattern was obvious throughout most of the day when the dolphins were in the bay, but was most common during the morning hours.

In the middle of the study, a large earthquake created a landslide in Kealakekua Bay that caused State authorities to completely close down the bay for all human activity for 2 weeks. Several structures in the nearby village of Napoʻo poʻo were also damaged and the volunteer observers had to abandon their regular observations and deal with the havoc that had been caused to their community. However, regularly scheduled observations were done on three days.

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As a result, this serendipitous natural experiment provided some valuable data on how the dolphins behaved when humans were absent. The dolphins appeared in the bay on all three days, for a 100% occupancy rate and the number of acrobatic aerial behavior dropped to less than 1/3 of what it had been. Some of the lower energy aerial behaviors dropped to less than 1/2 of what it had been, while the fast swim behavior did not change.

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After the complete closure period was over and people were allowed back into the bay again, the dolphins also went back to their pre-complete-closure behavior. The total number of high-energy behaviors (acrobatic, fast swim) was almost 4 times higher during the partial closure period compared to the complete closure period.

The information collected by the community volunteers shows that: a) the spinner dolphin resting area in Kealakekua was mostly used by people when dolphins are present, and the people are there to target the dolphins; b) rather than resting in these areas, the dolphins became much more active when people were within 100m of them, thus losing valuable resting time.

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In 2004 three different Hawaiʻi State-sponsored working groups discussed how to make the use of Kealakekua Bay more environmentally and culturally sensitive.  Each group met several times a month over several months and included key resident stakeholder groups.  One working group, dealing with all issues around the use of the waters in Kealakekua Bay, including diving and snorkeling tours, kayaking, and how to deal with all the resources in and around the bay, including the spinner dolphin resting area. This group agreed to recommend the establishment of a human exclusion, or Kapu zone, where the spinner dolphin resting area would be closed off with enough of a buffer zone to keep vessels and swimmers at least 100 meters away from the core resting area.  The only stakeholder group that chose not to participate in these meetings was the local swim-with-wild-dolphin community.

The data from this monitoring effort also suggest that the newly instituted rule by the National Oceanographic and Atmospheric Administration, that prohibits swimming with, approaching, or remaining within 50 yards of a Hawaiian spinner dolphin in Hawaiʻi be extended beyond 50m.

When in the bay, spinner dolphins spent the majority of their time within zone “B”, encompassing the majority of the core resting area, comparing well with early descriptions of how spinner dolphins used the bay between 1968 and 1981 (Norris and Dohl 1980, Norris et al. 1994).  Timmel et al. (2008) found a similar use pattern using a theodolite from a vantage point 69m above sea level, thus corroborating the data collected in this study.

The data presented here produced a mean number of swimmers within 45m (3.6) and 91m (4.0) about twice the size of those collected by theodolite, 1.6 and 1.9 respectively (Timmel et al. 2008).  The difference could be explained entirely by the previous study mostly collecting data between 0900 and 1300 hours, thus missing the peak in mean number of snorkelers (12.8/scan) during the 0800 hour (0800-0859) in this study.  The data on kayaks peaked later in the morning (1000 hour) and were much closer for the two studies, e.g. the number of kayaks within 91m of the dolphins were estimated at an average 2.5/scan in this study and 1.9/track by Timmel et al. (2008). Thus, estimates on distribution of different human user groups relative to the dolphins also compare well with theodolite-collected data. 

The first phase of this monitoring effort was organized as part of the State of Hawai'i sponsored Makai Watch Program while I was employed as the Big Island Marine Coordinator for The Nature Conservancy.  Alycia Bouyounan, Chris Wall, Nicole Killebrew and Nick Magel, from the Audubon Expeditions Institute, Lesley University dedicated two full days each to monitoring Kealakekua Bay at the start of this project.  Stephen Cornacchia headed up the effort in Kealakekua Bay during 2006, with Ann and Wes Jenkins continuing the monitoring effort into April of 2007. The three of them collected the crucial data during the complete closure period after the earthquake.  They were assisted by Glen Metheny, Ann Provacs and Marc Vandenplas.  Between November 2007 and October 2008, Nora Beck Judd, Steven Cornnacchia and Catherine Wynne collected the majority of the data.  They were assisted by Patty Eames, Glen Metheny, and Candace Miyatani.  Linda Preskitt helped coordinating this effort from the fall of 2007

Earlier drafts of this manuscript were edited by Marie Chapla, Jayne Lefors, Dr. Audre Brookes, Dr. Paul Nachtigall, Dr. Robert Gisiner, and Shannon Brownlee.  Statistical advice was provided by Joseph Eliahoo of the Statistical Advisory Service at Imperial College, London.  Funding was provided by the Hawaii Tourism Authority and NMFS.  I want to especially thank my family for all their support during the course of this project, including various efforts to get it published.