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Southern right whales (SRW) are capital breeders that use stored energy reserves to sustain themselves and their calves on nursery areas. With successful calving events declining in some SRW populations, it has been hypothesized that nutritional stress in adult females causes reproductive failure or death of calves shortly after birth. Here we compared offsets in carbon and nitrogen isotope values of mothers and their offspring (Δ13Ccalf‐cow and Δ15Ncalf‐cow) among three SRW populations. SRW from Aotearoa New Zealand, with high population growth rates and body conditions scores, have negative Δ13Ccalf‐cow suggesting calves are utilizing 13C‐depleted lipid carbon in milk to fuel the synthesis of nonessential amino acids used to build new tissues and rapidly grow. In contrast, a significantly positive Δ13Ccalf‐cow offset previously reported for SRW from Argentina during a mass die‐off event was hypothesized to be due to calves consuming milk with low lipid content. Patterns in Δ15Ncalf‐cow were more difficult to interpret and highlight the complexity in nitrogen transfer between mother and offspring. When combined with similar data collected from Brazil and during a low mortality year in Argentina, we hypothesize this approach provides a way to retrospectively compare nutritional condition of breeding adult female SRW across nursery areas. [ABSTRACT FROM AUTHOR]

As species recover from exploitation, continued assessments of connectivity and population structure are warranted to provide information for conservation and management. This is particularly true in species with high dispersal capacity, such as migratory whales, where patterns of connectivity could change rapidly. Here we build on a previous long-term, large-scale collaboration on southern right whales (Eubalaena australis) to combine new (n new ) and published (n pub ) mitochondrial (mtDNA) and microsatellite genetic data from all major wintering grounds and, uniquely, the South Georgia (Islas Georgias del Sur: SG) feeding grounds. Specifically, we include data from Argentina (n pub mtDNA/microsatellite = 208/46), Brazil (n new mtDNA/microsatellite = 50/50), South Africa (n new mtDNA/microsatellite = 66/77, n pub mtDNA/microsatellite = 350/47), Chile–Peru (n new mtDNA/microsatellite = 1/1), the Indo-Pacific (n pub mtDNA/microsatellite = 769/126), and SG (n pub mtDNA/microsatellite = 8/0, n new mtDNA/microsatellite = 3/11) to investigate the position of previously unstudied habitats in the migratory network: Brazil, SG, and Chile–Peru. These new genetic data show connectivity between Brazil and Argentina, exemplified by weak genetic differentiation and the movement of 1 genetically identified individual between the South American grounds. The single sample from Chile–Peru had an mtDNA haplotype previously only observed in the Indo-Pacific and had a nuclear genotype that appeared admixed between the Indo-Pacific and South Atlantic, based on genetic clustering and assignment algorithms. The SG samples were clearly South Atlantic and were more similar to the South American than the South African wintering grounds. This study highlights how international collaborations are critical to provide context for emerging or recovering regions, like the SG feeding ground, as well as those that remain critically endangered, such as Chile–Peru. [ABSTRACT FROM AUTHOR]