Genetic Diversity and Connectivity of Southern Right Whales (Eubalaena australis) Found in the Brazil and Chile–Peru Wintering Grounds and the South Georgia (Islas Georgias del Sur) Feeding Ground

Abstract

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 (nnew) and published (npub) 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 (npub mtDNA/microsatellite = 208/46), Brazil (nnew mtDNA/microsatellite = 50/50), South Africa (nnew mtDNA/microsatellite = 66/77, npub mtDNA/microsatellite = 350/47), Chile–Peru (nnew mtDNA/microsatellite = 1/1), the Indo-Pacific (npub mtDNA/microsatellite = 769/126), and SG (npub mtDNA/microsatellite = 8/0, nnew 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.

Historical reconstruction of the population dynamics of southern right whales in the southwestern Atlantic Ocean

“…Recently, satellite track data from animals tagged in northern Patagonia demonstrated substantial displacements from Uruguay to South Georgia (Islas Georgia del Sur) and the Scotia Sea (Mar de Escocia), suggesting that the SRW inhabits vast extensions of the south Atlantic Ocean and visits multiple potential feeding areas each season 45 . This result is also consistent with findings from isotopic analysis 46 – 48 , genetic studies 28 , 49 , 50 and whaling voyage logbooks that indicate a continuum in recorded catches along the South American Atlantic coastline 16 , 21 , 51 .…”

“…Recent evidence from genetic data indicates a connectivity between Brazil and Argentina. Samples from the South Georgia (Georgias del Sur) feeding ground were associated with wintering grounds in the South Atlantic, rather than the Indo-Pacific and were closer to the Argentinian and Brazilian wintering grounds than to the South-African 50 . The authors also suggested that the Chile-Peru population could have historically been a “stepping stone” between the south Atlantic and Indo-Pacific, rather than more closely linked to the southwest Atlantic wintering grounds as they had initially hypothesized.…”

Decadal shift in foraging strategy of a migratory southern ocean predator

“…Age classes (unaccompanied adults/juveniles) were visually determined based on the size of individuals, and adult‐nursing females (cows) were identified by the presence of calves. Previously collected samples include those collected from free‐ranging SRWs on South African coastal waters (Figure S1) from 1995 to 1997 (biopsy samples stored in dimethyl sulfoxide, DMSO; Best et al, 2003) and 2015–2016 (sloughed skin stored in ethanol; Carroll et al, 2020). The effect of DMSO storage is removed by lipid extraction (Burrows et al, 2014; Busquets‐Vass et al, 2017; Newsome et al, 2018; Todd et al, 1997) and storage in ethanol has no effect on the isotopic composition of animal tissues (Hobson et al, 1997).…”

Antofagasta Region in northern Chile, a potential nursing ground for the Southern right whale Eubalaena australis

“…More comparative research (e.g. Carroll et al, 2020) including photo-identification and phylogenetic studies of SRW from South Africa, South Georgia, Argentina, and Chile-Peru will be needed to understand migratory paths, genetic flux between (sub)populations and degree of philopatry. Due to slow swimming and nearshore distribution in the breeding season, globally SRW is the fourth cetacean species most prone to die or be severely injured from vessel collision 5 .…”