Identifying Important Habitat for Spinner Dolphins of East Hawaii

In Fall 2018, TDI launched a new effort to identify important habitat for spinner dolphins found off east Hawaii Island to learn how they use these often rougher coastal areas, and the degree to which the spinner dolphins found in bays and along the east (windward) Hawaii Island are different from those found off the west (leeward) coast.

One of the most visible resident dolphin species found off Hawaii, Hawaiian spinner dolphins are nocturnal feeders. To sustain themselves, they spend evening and early morning hours hunting offshore, and then return during daylight to shallow bays, coves and shorelines to rest and socialize. Daytime rest is critical to a spinner dolphin’s overall health and fitness, and may be compromised by chronic disturbance. Unfortunately, in recent years, Hawaiian spinner dolphins have faced increasing pressures in their resting areas from an increase in the number of people seeking close encounters. TDI’s early studies of Hawaiian spinner dolphins focused on identifying how often individual dolphins observed off Oahu’s leeward side were seen in conjunction with human swim encounter activities. We also participated in a collaborative study to identify key features associated with their most oft-used habitat. However, most of these efforts focused on spinners found along leeward or southern shores.

Understanding how spinner dolphins use the windward shores of Hawaii Island is critical, especially given that starting in May 2018, lava flows into the sea off east Hawaii dramatically altered the coastline including eliminating some shallow bay areas. TDI will be monitoring dolphin presence and activities using long-term using autonomous underwater acoustic recording devices called “Sound-traps.” These devices sit on the sandy bottom and record the acoustic soundscape. Thus, our goals are to monitor long-term the daily, seasonal and yearly trends in acoustic behavior of Hawaiian spinner dolphins along east Hawaii, and to learn about which bays, coves and coastlines serve as the most important habitat for these animals. While listening for spinners underwater, we will also be launching regular boat-based surveys to photo-identify individual spinners and match these to catalogs of spinners from west Hawaii to better understand the extent to which spinner dolphins observed off east Hawaii are permanent or temporary residents to that area.