Bioacoustics of Lagenorhynchus albirostris

BEHAVIOR Lagenorhynchus albirostris , like other delphinids, shows tendencies to form social groups. Most reports are of average group sizes of less than 10 animals ( United States and Canada— Cetacean and Turtle Assessment Program 1982 ; Alling and Whitehead 1987; Kingsley and Reeves 1998; Greenland— Hansen and Heide-Jørgensen 2013; Iceland—Pike et al. 2009; North Sea and United Kingdom—Evans 1992; Kinze et al. 1997 ; Reid et al. 2003 ; Weir et al. 2009 ; Norway—Øien 1996; Barents Sea—Fall and Skern-Mauritzen 2014). Large social groups from Iceland have up to 100 individuals ( Pike et al. 2009 ) and even larger groups are known from the Barents Sea (Fall and Skern- Mauritzen 2014). Off West Greenland , large groups used depths of 300–1,000 m and smaller groups tended to use deeper waters (> 1,000 m—Hansen and Heide-Jørgensen 2013). Studies of acoustics and hearing in free-ranging L . albirostris off Iceland have estimated the 3 and 10 dB beamwidths of the echolocation signals to be 8° and 10°, respectively, significantly narrower than in the bottlenose dolphin ( Rasmussen et al. 2004 ). The echolocation clicks of L . albirostris off Iceland have average peak frequencies around 115 kHz with a secondary peak around 250 kHz, and a center frequency at around 82 kHz (Rasmussen and Miller 2002; Rasmussen et al. 2002). Click source level (the effective level of sound intensity) varies from about 190–210 dB re. 1 µPa, increasing with the distance to the target (Rasmussen et al. 2002; Atem et al. 2009 ). The maximum source level recorded is about 219 dB re. 1 µPa peak-to-peak (Rasmussen et al. 2002). When socializing, whistles vary in frequency up to 35 kHz (Rasmussen and Miller 2002). Whistles can potentially be used for communication at distances up to 10.5 km ( Rasmussen et al. 2006 ). Hearing studies in 2 captured and restrained dolphins from western Iceland ( Nachtigall et al. 2008 ) revealed highest sensitivities between 45 and 128 kHz. In one dolphin, detection threshold at 152 kHz was at 100 dB and at 181 kHz at 121 dB, indicating that L . albirostris has more sensitive high-frequency hearing than any known dolphin. The capability for temporal resolution of sound, when tested in one of the caught dolphins ( Mooney et al. 2009 ), revealed the dolphin could follow rhythmic clicks up to a rate of about 1,125 –1,250 Hz, a similar capability to other odontocetes. Mean pulse rate for supposed communication burst-pulse signals was at 719 Hz (range 423–1,103), with a mean peak frequency of 35.3 kHz ( Simard et al. 2008 ). Lagenorhynchus albirostris sometimes approaches vessels and rides their bow waves ( Jonsgård 1962 ; de Boer 1989 ; Evans 1991 ) and frequently leaps out of the water, often vertically (Sears and Williamson 1982; Katona et al. 1983 ; Baptist 1987 ). Although it usually travels at 6–12 km /h, speeds of 30 km /h are known from the North Sea area (Evans and Smeenk 2008). A juvenile male from Faxaflói Bay in western Iceland ( Rasmussen et al. 2013 ) dove to 45 m (mean dive depth: 24 m ) in dives up to 78 s (mean: 28 s). More than one-half of the feeding activity seemed to occur at the sea floor. GENETICS Moderate variation of mitochondrial as well as nuclear markers in a sample of Lagenorhynchus albirostris from the United States and Canada , the United Kingdom , the Netherlands , and northern Norway (Banguera-Hinestroza et al. 2010) indicate a population contraction, possibly during the last glacial epoch. Fernandez et al. (2016) mapped 52,981 nuclear single nucleotide polymorphisms in L. albirostris and L. acutus . Studies of the mitochondrial genome ( Xiong et al. 2009 ; Vilstrup et al. 2011 ), mitochondrial and nuclear markers (Harlin-Cognato and Honeycutt 2006; Banguera-Hinestroza et al. 2014), and mitochondrial sequences ( Cipriano 1997 ; LeDuc et al. 1999 ) show that L . albirostris is not related to its putative Pacific and Southern ocean relatives formerly included in the Lagenorhynchus genus. It may be the sole extant representative of a long-lasting independent taxon, which is possibly the sister taxon of the remaining Delphinidae , although the studies opening this possibility ( Xiong et al. 2009 ; Vilstrup et al. 2011 ) did not include L . acutus in their study. One study ( LeDuc et al. 1999 ) did not find a close affinity between L . acutus and L . albirostris , but Harlin-Cognato and Honeycutt (2006) and Banguera-Hinestroza et al. (2014) supported monophyly of the 2 species.