Abstract
There are multiple blue whale acoustic populations found across the Southern Hemisphere. The different subspecies of blue whales feed in separate areas, but during their migration to lower-latitude breeding areas each year, Antarctic blue whales become sympatric with pygmy and Chilean blue whales. Few studies have compared the degree of this overlap of the Southern Hemisphere blue whale subspecies across ocean basins during their migration. Using up to 16 years of acoustic data, this study compares the broad seasonal presence of Antarctic blue whales, Chilean blue whales, and Southeast Indian Ocean (SEIO) pygmy blue whales across the Pacific and Indian Oceans. Antarctic blue whales were sympatric with the other two blue whale subspecies during the migrating season of every year. Despite this overlap, Chilean and pygmy blue whale detections peaked earlier during the austral autumn (April–May) while Antarctic blue whale detections peaked later during the austral winter (June). Chilean (Pacific Ocean) and SEIO (Indian Ocean) pygmy blue whales showed similar seasonal patterns in detections despite occurring in different ocean basins. Though we have shown that Antarctic blue whales have the potential to encounter other blue whale subspecies during the breeding season, these distinct groups have remained acoustically stable through time. Further understanding of where these whales migrate will enable a better insight as to how these subspecies continue to remain separate.
Highlights
Sympatric populations are groups of conspecifics that coexist spatially with limited to no gene flow between them
Our results show that blue whales living in temperate waters (Chilean and Southeast Indian Ocean (SEIO) pygmy acoustic populations) had similar seasonal migration patterns, and differed from the Antarctic blue whales
We show that Antarctic blue whale presence is similar between the Pacific and Indian Oceans
Summary
Sympatric populations are groups of conspecifics that coexist spatially with limited to no gene flow between them. Unlike allopatric populations, there are no physical barriers separating sympatric groups. Evidence of sympatric populations includes the highly diverse cichlid species found in the East African Great Lakes and the Midas cichlid species complex found in Nicaraguan. A more recent example of sympatric speciation in the last 200 years is found in the apple maggot, Rhagoletis pomonella (Filchak et al, 2000). This species of fruit fly originally colonized wild hawthorn in the eastern parts of North America, but with the introduction of apples in the mid-1800 s, R. pomonella was able to adapt to a new host. Today there are two distinct groups of R. pomonella, one living on hawthorn and the other living on apple
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