Vol. 423: 261–268, 2011 MARINE ECOLOGY PROGRESS SERIES Published February 10 doi: 10.3354/meps08959 Mar Ecol Prog Ser OPENPEN ACCESSCCESS Humpback whale Megaptera novaeangliae song reveals wintering activity in the Northwestern Hawaiian Islands Marc O. Lammers1, 2,*, Pollyanna I. Fisher-Pool2, Whitlow W. L. Au1, Carl G. Meyer1, Kevin B. Wong3, Russell E. Brainard3 1Hawaii Institute of Marine Biology, University of Hawaii, 46-007 Lilipuna Rd., Kaneohe, Hawaii 96744, USA 2Joint Institute for Marine and Atmospheric Research, University of Hawaii, 1000 Pope Road, MSB312, Honolulu, Hawaii 96822, USA 3NOAA Fisheries, Pacific Islands Fisheries Science Center, Coral Reef Ecosystem Division, 1125 B Ala Moana Blvd., Honolulu, Hawaii 96814, USA ABSTRACT: The main Hawaiian Islands (MHI) are the principal breeding ground for humpback whales in the North Pacific. Over the past 3 decades, population recovery from whaling-era losses has resulted in a steady increase in the number of whales wintering in Hawaiian waters and a geo- graphic expansion of their distribution in the MHI. Until recently, no existing evidence showed that this expansion included the islands, atolls, and banks of the Northwestern Hawaiian Islands (NWHI). To better understand the occurrence of humpback whales in the NWHI, 9 ecological acoustic recorders (EARs) were deployed at sites throughout the archipelago to record the occurrence of humpback whale song, an indicator of winter breeding activity. Song was found to be prevalent at Maro Reef, Lisianski Island, and French Frigate Shoals but was also recorded at Kure Atoll, Midway Atoll, and Pearl and Hermes Atoll. Both the timing and abundance of song at several locations closely followed trends observed on Oahu, which is one of the MHI, strongly suggesting that humpback whales use the NWHI as a wintering area. This finding is of particular relevance in light of recent suggestions that, based on photo-identification data, a yet undocumented wintering area exists somewhere in the central North Pacific. We propose that the NWHI could be that area. KEY WORDS: Humpback whale · Acoustics · Hawaiian Islands · Wintering grounds · Ecological acoustic recorder · EAR Resale or republication not permitted without written consent of the publisher INTRODUCTION United States Endangered Species Act is currently underway (Federal Register 2009). Humpback whales Megaptera novaeangliae in the Humpback whales are migratory and hold the North Pacific were heavily depleted by whaling during record for the longest migration distance of any mam- the first half of the 20th century. It is estimated that in mal (~8300 km; Rasmussen et al. 2007). Migrations are 1966, when commercial whaling ceased, the number of made by all age classes and both genders of the spe- animals had been reduced to between 1200 (Johnson & cies (Dawbin 1966). During the fall months, whales Wolman 1984) and 1400 (Gambell 1976) animals. Since travel from high to low latitudes and spend the winter the 1970s, however, numbers have steadily increased, months engaged in activities related to reproduction, and now the total abundance in the North Pacific including giving birth, nursing newborn calves, wean- is estimated at ~20 000 whales (Calambokidis et al. ing yearlings, and competing for mates (Darling & 2008). As a result, a review of their status under the Jurasz 1983, Darling & McSweeney 1985, Baker et al. *Email: [email protected] © Inter-Research 2011 · www.int-res.com 262 Mar Ecol Prog Ser 423: 261–268, 2011 1986). In late winter and spring, the route is reversed National Monument (PMNM), one of the largest marine and whales return to more biologically productive protected areas in the world. Because they are so re- higher latitudes to spend the summer months feeding mote, most islands and banks in the NWHI are visited (Baker et al. 1986, Calambokidis et al. 2001). infrequently by humans, particularly during winter One of the behavioral characteristics of males on the months when ocean conditions are generally hazard- breeding grounds is the production of an elaborate dis- ous to mariners. Historically, humpback whales were play of song (Payne & McVay 1971, Winn & Winn not thought to occur in the NWHI (Herman & Antinoja 1978). Humpback whale song is complex, with acousti- 1977, Herman 1979), but in 2006, a National Oceanic cally distinct units ordered into phrases and themes and Atmospheric Administration (NOAA) cetacean (Payne & McVay 1971, Frumhoff 1983, Payne et al. survey reported multiple sightings, suggesting a larger 1983, Au et al. 2006). Males on the same wintering presence than previously believed (Johnston et al. ground and in the same breeding population sing ap- 2007). proximately the same song (Winn & Winn 1978, Hel- The present study examined the occurrence of weg et al. 1998, Cerchio et al. 2001), but the song dif- humpback whales in the NWHI using an acoustic fers in content between breeding populations (Payne & monitoring approach similar to the one employed by Guinee 1983). There is presently no consensus about Au et al. (2000). Bottom-moored, long-term recorders the behavioral function of song, but several explana- deployed in both the NWHI and MHI were used to tions have been proposed, including: a display of fit- meet 3 specific objectives: (1) to determine whether ness to females (Winn & Winn 1978, Tyack 1981, Smith humpback whales engage in wintering behavior in et al. 2008), a display to other males (Darling et al. the NWHI as indicated by the presence of male 2006), an orientation signal used as a migratory beacon singing behavior; (2) to establish where in the NWHI by other whales (Clapham & Mattila 1990), a spacing archipelago whale occurrence is highest; and (3) to mechanism between males (Frankel et al. 1995), an determine whether/how the timing of occurrence in acoustic stimulus to induce female estrous (Baker & the NWHI is different from known wintering areas Herman 1984), and the production of a sonar signal to in the MHI. help males locate females (Frazer & Mercado 2000). Irrespective of the function, the occurrence of song in an area is an excellent indicator of humpback whale MATERIALS AND METHODS presence. Au et al. (2000) demonstrated that the sound pressure level of chorusing (song produced by multiple The presence of wintering humpback whales was males) changes over the course of the breeding season established by monitoring shallow waters in the NWHI and is a reliable metric for establishing the timeline of for the incidence of song using bottom-moored ecolog- arrival, peak density, and departure of whales on the ical acoustic recorders (EARs) (Lammers et al. 2008). wintering ground. The EAR is a microprocessor-based autonomous re- The main Hawaiian Islands (MHI) are the principal corder that samples the ambient sound field on a pro- wintering ground for North Pacific humpback whales. grammable duty cycle. Between 11 June and 4 Octo- Between 8500 and 10 000 whales, or nearly half of the ber 2008, 7 EARs were deployed in the NWHI through estimated basin-wide population, migrate to Hawaii a collaborative partnership between the Hawaii Insti- each winter (Calambokidis et al. 2008). Other known tute of Marine Biology, the PMNM, and the NOAA wintering areas in the North Pacific include the Oga- Pacific Islands Fisheries Science Center. The EARs sawara Islands, Okinawa, Taiwan, the Philippines, the were programmed to record for 30 s every 15 min at a Mariana Islands, Baja California, the Pacific coast of sampling rate of 40 kHz. To compare results obtained Mexico, the Revillagigedo Archipelago, and the Pacific in the NWHI with the occurrence of humpback whale coasts of Guatemala, El Salvador, Nicaragua, and song in the MHI, 2 EARs were also deployed off the Costa Rica (Calambokidis et al. 2008). island of Oahu at sites known to have high whale In Hawaii, a steady increase in the number of whales abundance during winter months. The deployment overwintering has resulted in an expansion of their dis- locations, depths, and recording periods of each EAR tribution across the main archipelago (Mobley et al. are shown in Fig. 1 and Table 1. 1999). Still unresolved is the extent to which this ex- Data obtained from each EAR were processed using pansion has included the Northwestern Hawaiian a custom Matlab script. An automated short-time Islands (NWHI), a chain of remote, mostly uninhabited Fourier-transform approach was used to find periods atolls, small islands, and shallow banks stretching where tonal peaks greater than 3 dB above the aver- 2000 km to the northwest of the MHI (see Fig. 1). In aged noise floor were present in the frequency spec- 2006, these islands and their associated offshore waters trum below 2 kHz (Lammers et al. 2008). These peri- were designated the Papahanaumoku– akea– Marine ods were summed for each recording and those with Lammers et al.: Humpback whale song reveals wintering activity 263 Fig. 1. Locations of the ecological acoustic recorders (EARs; s) in the Hawaiian Archipelago tonality exceeding 1% of the total recording time percent tonality and then visually examined using the were considered to potentially contain whale song. To program CoolEdit™ (Adobe). For each day, record- establish daily presence or absence of song at each ings were examined serially until either whale song site, recordings for each day were ranked by their was confirmed or all files with tonality exceeding 1% were exhausted. In addition, to inves- Table 1. Location, deployment depth, and recording period of each ecological tigate the relative abundance of song acoustic recorder (EAR). Dates in parentheses indicate that the EAR stopped by location and across time, 10% of recording prior to the end of the wintering season (Kure Atoll and FFS2) or that recordings from each site were ran- the EAR was deployed following the start of the season (Makapu‘u). FFS1 and FFS1: French Frigate Shoals sites 1 and 2 domly selected for each month and visually and aurally examined for the presence of song.