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.
Is male humpback song an honest indicator of a male’s fitness and fertility?
One of the most recognizable and well-studied vocalizations among any whale species is the song of humpback whales (click here to hear a singer off Maui). Sung exclusively by males and primarily on breeding grounds, humpback whale song is a complex series of repeated vocalizations (i.e. units) that can range in frequency from 100 Hz to 4 kHz with harmonics extended up to at least 24 kHz, and have amplitudes as high as 174 dB re 1 μPa. In shallow water habitats, humpback whale song may travel as far as 10 km. At any one time within a breeding ground, all singers converge on the same version of the song, although across a season portions of song may change. Song convergence across greater distances and different breeding grounds within the same oceanic basin indicate that song is a culturally transmitted vocalization. Since the start of our humpback whale project by Dr. Louis M. Herman, the quest to understand humpback whale song has been at the forefront of our studies as witnessed from his inaugural proposal of song as part of a lek mating system in which males congregate and display in an area without resources that females visit for mating (Herman and Tavolga, 1980). Since that time, many studies by our laboratory and others have been conducted describing humpback whale song and singing behavior, examined which males sing, and investigated how other humpbacks respond to playback of song (summarized in Herman, 2017). However, despite agreement among scientists that humpback whale song is inextricably linked to the humpback whale mating system, its functions remain a matter of debate. To learn whether the song produced by individual males is an honest display of their fitness and fertility, TDI researchers have been working together with Dr. Marc Lammers, research coordinator for the Hawaiian Islands Humpback Whale National Marine Sanctuary and Founder of Oceanwide Science Institute, in waters off Maui to identify individual singers and examine whether acoustic characteristics of a singer’s song are correlated with his body size and level of testosterone. To obtain all these data, we first deploy a hydrophone from our small boat, listen closely and isolate the song from one singer from the chorus of singers in the neighborhood and use increasing loudness of the song to locate the singer. With the singer located, we first identify it by photographing its tail flukes, which we will later match to our archival catalog to reveal the life history of this whale. Next, two snorkelers carefully enter the water, one equipped with an audio/video system to make calibrated acoustic recordings of the whale’s song and the second equipped with a video camera and hand-held high-frequency sonar device to measure the whale’s body length using an underwater videogrammetric technique developed by TDI researchers. Once the recordings are made and measurements taken, the team returns to the boat and uses a crossbow and arrow with sterile tip to obtain a small biopsy sample from the singer. The sample is frozen and sent to the laboratory of collaborator Dr. Shannon Atkinson of University of Alaska, Fairbanks for processing and measurement of testosterone level. As is evident, to collect full data on each singer is a lengthy process. Thus far, we have analyzed body sizes and acoustic characteristics on seven singer with correlation results looking very promising!
What types of vocalizations do humpback whale mothers and calves use to communicate?
In 1977, TDI’s Dr. Lou Herman and colleague Ron Antinoja published one of the first scientific papers documenting the distribution and behavior of humpback whales in Hawaiian waters. They showed that most humpbacks are found within the 183 meter (600 feet) contour of the main Hawaiian Islands and that mother-calf pairs were often found in even shallower waters. Since then, TDI researchers have shown that mother-calf pairs segregate themselves into shallow waters to avoid energetically costly associations with males seeking mating opportunities, but that their habitat “footprint” extends into deeper waters as a calf ages and grows. Additionally, when in deeper water, they favor areas associated with rugged seabed terrain over flat seabed terrain. Rugged terrain tends to be noisy from snapping shrimp and may thus provide acoustic “camouflage” for mother and calf vocalizations being detected by eavesdropping males. Thus, even in deep waters mothers appear to continue to employ tactics to avoid males. Although mother-calf habitat use has been studied extensively in Hawaiian waters, relatively little is known about their vocalizations in the breeding grounds. To describe and better understand the function of vocalizations of mothers and their calves, TDI researchers, in collaboration with former Ph.D. student Jessica Chang, Dr. Whitlow Au of Hawaii Institute of Marine Biology and Dr. Marc Lammers of the Hawaiian Islands Humpback Whale National Marine Sanctuary, have been deploying acoustic and data recording suction cup tags on the backs of humpback whale mothers and calves. The tags continuously record whale vocalizations in conjunction with a whale’s depth and geometry in space, thus allowing our researchers to investigate what sounds mothers and calves produce, when and where they vocalize, and if they coordinate their vocalizations with each other. Since 2014, we have successfully deployed 11 tags on seven mothers and four calves as well as on a lone female without a calf and a male in a dyad that left its affiliate and started to sing. Over 60 hours of recordings have been accumulated. Calls recorded from tags on calves and mothers occurred singly or in bouts and were brief compared to male song. Thus far we have identified 381 calls falling into 12 call types with frequency upsweep calls and pulsed calls are most common. The maximum depth reached by tagged mothers and calves was similar at just over 100 m. In our continuing efforts to study humpback whale mother-calf vocalizations, we are striving to deploy tags on both the mother and the calf in the same group to better resolve vocal exchanges between the two. In combination with these data, we will also measure calf size using our videogrammetric technique or alternatively using drone technology to examine calf vocalizations and mother-calf communications as a function of calf age and development.
Does humpback whale fidelity to particular feeding grounds and feeding groups in Southeast Alaska extend over decades?
After spending weeks, and occasionally months, in warm Hawaiian waters engaging in activities related to breeding and calving, North Pacific humpback whales migrate northward to high latitude colder nutrient rich waters off Alaska, the Aleutian Islands and other areas along the North Pacific rim. This journey of several thousand miles will take them into nutrient rich waters where, after fasting in Hawaii, they can feed on swarming krill and small schooling fish such as herring, capelin, and sand lance. In 1980, TDI’s Lou Herman traveled with his family and several students from Hawaii to Southeast Alaska for the first time to document the identities and behaviors of North Pacific humpback whales in their feeding grounds. They found many of the same whales they had seen for years in Hawaiian waters and marveled as they gorged themselves on prey using a variety of hunting tactics. One of these methods involved small groups of whales cooperatively hunting herring. The group would dive below a school of herring and create a ring of bubbles to contain the school. One of the whales then produced a loud trumpet like “feeding call.” After several bouts of the call, the bubble ring appeared at the surface and a few seconds later the whale burst through with mouths agape and filled with herring. From 1980-1987, Dr. Herman and his students and colleagues demonstrated the high fidelity of humpbacks between Hawaii and various feeding areas in Alaskan waters. They also documented the same whales joining together across summers to feed cooperatively on herring schools. Between 1988-2006, TDI researchers focused their studies exclusively on humpbacks in Hawaiian waters. However, in 2007, TDI’s Adam Pack joined forces with Captain Dennis Rogers in Petersburg, Alaska to reinitiate TDI’s Alaska whale research in conjunction with a program enabling participants to assist in the work. The goals of these new studies are to examine the extent to which the same whales documented in the 1980’s would be found again in the same Alaskan waters, to investigate long-term associations in cooperative feeding groups, and to see whether any of these associations persisted on the Hawaiian breeding grounds. Thus far, well over 1000 humpbacks have been identified in the waters of Frederick Sound, Alaska and its various straits and inlets. Many of these whales are seen annually and are also archived in TDI’s long-term database from Alaska and Hawaii. The research has also revealed several “core groups” of whales that appear to come together annually to hunt herring cooperatively and in several instances adopt the same behavioral roles in these teams. In 2015, Pack and colleagues recognized and photographed a whale they called “Old Timer.” With a span between first and last sighting of 44 years, the archival record revealed this whale to have the longest resighting span of any in the world. Future work will continue to trace the life histories of Hawaii’s humpbacks in waters off southeast Alaska and the nature of their long-term associations. We are also collaborating with other whale researchers in Alaska including Dr. Shannon Atkinson and Kelly Cates from University of Alaska Fairbanks to collect biopsy samples from females in Alaska to determine rates of pregnancy, and from males to explore how their testosterone levels vary and whether testosterone increases are associated with song production towards the end of the feeding season.