Biogeographic characterisation of blue whale song worldwide: using song to identify populations

Abstract

Blue whale songs provide a measure for characterising worldwide blue whale population structure. These songs are divided into nine regional types, which maintain a stable character. Five of the nine song types have been recorded over time spans greater than 30 years showing no significant change in character. The nine song types can be divided into those containing only simple tonal components (high latitude North Pacific, North Atlantic and Southern Ocean song types), those comprised of complex pulsed units in addition to the tonal components (Pacific Ocean margin song types from California, Chile and New Zealand), and those which have the greatest complexity of all and the longest cycling times (Indian Ocean song types from Sri Lanka, Fremantle and Diego Garcia). We suggest that temporally stable differences in song provide another characteristic for comparison with genetic and morphological data when defining blue whale populations. Furthermore, as Mellinger and Barlow (2003) recommend, when there is a lack of other data or lack of clarity in other data sets, evidence of distinct differences in songs between areas should be used as a provisional hypothesis about population structure when making management decisions. Worldwide study is needed to better understand the various populations and subspecies within species like the blue whale that have large geographic distributions and have both migrating and resident populations.

Geographic variation in external morphology of North Pacific and Southern Hemisphere blue whales (Balaenoptera musculus)

“…Distribution and acoustic studies suggest that the region extending south from the Equator to northern Peru and west of the Galapagos Islands may be habitat (at least seasonally) for blue whales from at least two different populations (McDonald et al, 2006). One population, studied near the Galapagos Islands, is thought to be related to the Antarctic blue whale and migrates during the austral spring to feeding grounds close to Antarctica (Palacios, 1999;Stafford et al, 2004).…”

Blue (Balaenoptera musculus) and fin (B. physalus) whale vocalisations measured from northern latitudes of the Atlantic Ocean

“…Passive acoustic techniques are increasingly being used to monitor cetacean populations. They have recently been used to assess issues relevant to management of mysticete populations, including density estimation (McDonald and Fox, 1999), geographic variability (McDonald et al, 2006;Mellinger and Clark, 2003;Stafford et al, 2001), seasonality (Clark and Clapham, 2004;Moore et al, 1998;Northrop et al, 1971) and migratory behaviour (Clark and Ellison, 2000;Stafford et al, 1999). These techniques can allow cost-effective, remote monitoring over long periods of time.…”

Geographic differences in Blainville's beaked whale (Mesoplodon densirostris) echolocation clicks

“…physalus ) whale song has provided insight into population structure in these species (e.g. Archer et al, 2020; Delarue et al, 2009; Helble et al, 2020; McDonald et al, 2006; Širović et al, 2017). The population‐level acoustic differentiation appears to be more stable in blue than fin whales (Helble et al, 2020; Širović et al, 2017).…”