Humpback whale song recordings suggest common feeding ground occupation by multiple populations

Abstract

Humpback whale males are known to sing on their low-latitude breeding grounds, but it is well established that songs are also commonly produced ‘off-season’ on the feeding grounds or during migration. This opens exciting opportunities to investigate migratory aggregations, study humpback whale behavioral plasticity and potentially even assign individual singers to specific breeding grounds. In this study, we analyzed passive acoustic data from 13 recording positions and multiple years (2011–2018) within the Atlantic sector of the Southern Ocean (ASSO). Humpback whale song was detected at nine recording positions in five years. Most songs were recorded in May, austral fall, coinciding with the rapid increase in sea ice concentration at most recording positions. The spatio-temporal pattern in humpback whale singing activity on Southern Ocean feeding grounds is most likely shaped by local prey availability and humpback whale migratory strategies. Furthermore, the comparative analyses of song structures clearly show a differentiation of two song groups, of which one was solely recorded at the western edge of the ASSO and the other song group was recorded throughout the ASSO. This new finding suggests a common feeding ground occupation by multiple humpback whale populations in the ASSO, allowing for cultural and potentially even genetic exchange among populations.

Return of large fin whale feeding aggregations to historical whaling grounds in the Southern Ocean

“…Fin whales occur in both, the South Pacific and the South Atlantic 72 , therefore both Oceans are candidate areas of origin for these fin whales. Mixing of breeding stocks at feeding grounds is known from humpback whales 73,74 . But the population structure of Southern Hemisphere fin whales is not yet understood [75][76][77] , and the locations of lower latitude breeding or wintering grounds are unknown 78 .…”

Song recordings suggest feeding ground sharing in Southern Hemisphere humpback whales

“…Specific feeding areas, for example, can be visited during most years, but are abandoned during years with exceptional climatic conditions 10 . This migratory plasticity facilitates the mixing of populations within feeding aggregations allowing for cultural and genetic exchange 3 , 5 , 11 , 12 .…”

“…The songs of male humpback whales can be recorded mainly during late autumn, winter, and early spring (i.e., shortly before, during and shortly after the breeding period of humpback whales) and are highly similar among males within a breeding population, but are (to some extent) distinct among males from different breeding populations 14 , 16 . Especially for areas with restricted access, such as the Southern Ocean, the possibility of investigating migratory linkages between breeding and feeding grounds through the comparison of population-specific humpback whale songs is a great advance for humpback whale population monitoring 4 , 12 , 17 , 18 . The availability of long-term passive acoustic monitoring data from the Southern Ocean and the discovery that humpback whales sing extensively while on the Southern Ocean feeding grounds and migration routes 12 , 19 – 21 now allows for the exploration of song similarity between breeding and feeding grounds which can be used as an indicator for population mixing 4 , 17 , 22 .…”

“…Especially for areas with restricted access, such as the Southern Ocean, the possibility of investigating migratory linkages between breeding and feeding grounds through the comparison of population-specific humpback whale songs is a great advance for humpback whale population monitoring 4 , 12 , 17 , 18 . The availability of long-term passive acoustic monitoring data from the Southern Ocean and the discovery that humpback whales sing extensively while on the Southern Ocean feeding grounds and migration routes 12 , 19 – 21 now allows for the exploration of song similarity between breeding and feeding grounds which can be used as an indicator for population mixing 4 , 17 , 22 .…”

“…The Atlantic sector of the Southern Ocean (ASSO) is regularly frequented by humpback whales and its Northern limit (i.e., in the vicinity of the Antarctic Polar Front) is especially suitable feeding habitat for humpback whales 10 , 23 – 25 . At least two distinct humpback whale breeding populations have been found to visit and overlap within the ASSO 5 , 12 , 26 and a high similarity in songs from South Atlantic breeding areas suggests occasional mixing of populations, potentially on a common feeding ground 4 . To gain a more comprehensive understanding of how many and which humpback whale populations mix in the ASSO, this study aims to conduct comparative analysis of humpback whale songs from the ASSO and available temporally matching song recordings from the Ecuadorian (breeding stock G 27 ) and Brazilian (breeding stock A 27 ) breeding grounds and the Chilean, Namibian, and western South African migration routes/mid-latitude feeding grounds (of breeding stocks G and B, respectively; assumed migratory connections by the IWC 27 ).…”