The Southern Ocean Exchange: porous boundaries between humpback whale breeding populations in southern polar waters

Abstract

Humpback whales (Megaptera novaeangliae) are a cosmopolitan species and perform long annual migrations between low-latitude breeding areas and high-latitude feeding areas. Their breeding populations appear to be spatially and genetically segregated due to long-term, maternally inherited fidelity to natal breeding areas. In the Southern Hemisphere, some humpback whale breeding populations mix in Southern Ocean waters in summer, but very little movement between Pacific and Atlantic waters has been identified to date, suggesting these waters constituted an oceanic boundary between genetically distinct populations. Here, we present new evidence of summer co-occurrence in the West Antarctic Peninsula feeding area of two recovering humpback whale breeding populations from the Atlantic (Brazil) and Pacific (Central and South America). As humpback whale populations recover, observations like this point to the need to revise our perceptions of boundaries between stocks, particularly on high latitude feeding grounds. We suggest that this “Southern Ocean Exchange” may become more frequent as populations recover from commercial whaling and climate change modifies environmental dynamics and humpback whale prey availability.

Song recordings suggest feeding ground sharing in Southern Hemisphere humpback whales

“…Due to maternally directed site fidelity, humpback whales usually return every year to their natal breeding ground, dividing Southern Hemisphere humpback whales into at least six distinct breeding populations 1 . The connectivity among these breeding populations usually correlates with the geographical distance between the areas, but most likely also depends on the degree of longitudinal movements of individuals within the Southern Ocean 2 – 5 . Humpback whales are flexible in their ecological requirements and are able to adapt to environmental change with alternative migration and feeding strategies 5 – 9 .…”

“…The connectivity among these breeding populations usually correlates with the geographical distance between the areas, but most likely also depends on the degree of longitudinal movements of individuals within the Southern Ocean 2 – 5 . Humpback whales are flexible in their ecological requirements and are able to adapt to environmental change with alternative migration and feeding strategies 5 – 9 . Specific feeding areas, for example, can be visited during most years, but are abandoned during years with exceptional climatic conditions 10 .…”

“…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 .…”

Individual and joint estimation of humpback whale migratory patterns and their environmental drivers in the Southwest Atlantic Ocean

“…The migratory routes and destinations documented in this study confirms the areas around the SS represent an important feeding ground for SWA humpback whales. Previously, migratory connectivity was established by satellite tracking (including some of the tracks used in the present analysis 7 , 41 , 42 and photo-identification data 38 , 40 , 61 showing whales used habitats close to SG and the SSI. This study adds new migratory connections for humpback whales wintering off Brazil, including foraging areas near the SO, the South-Scotia and North Weddell ridges, Weddell Sea, and the Maud Rise/Lazarev Sea (Figs.…”

“…The aforementioned conditions result in defining the dynamic feeding grounds for SWA humpback whales, which might be experimenting drastic modifications during the last years. It worth consideration though, that recent photo-identified SWA humpback whales at Western Antarctic Peninsula 61 suggests that population recovery 34 might promote that some individuals start using new and/or reoccupy historical areas. Continued, long-term monitoring of movements and habitat use of this population will help refining the results of this study and understanding how whales will respond to ongoing habitat modifications and population expanse.…”