Abstract
Seabirds are amongst the most threatened avian groups, with 30% classified as globally threatened. Major threats to Procellariiformes (albatrosses, petrels, and shearwaters) include fisheries bycatch, introduced predators, and climate change. Cryptic species and a poorly resolved taxonomy can obscure true biodiversity and lead to misinformed conservation priorities. Despite their wide-ranging movements, many seabird populations exhibit genetic structuring, making population-level genetic assessments crucial for evaluating a species' vulnerability and informing evidence-based conservation management guidelines.
Toroa Buller’s albatross (Thalassarche bulleri), which are endemic to Aotearoa New Zealand, breed only on offshore islands. The species is currently classified as two subspecies based on asynchronous breeding schedules: northern T. b. platei (Chatham Islands, October–May) and southern T. b. bulleri (Snares and Solander, January–August). An additional small population (<40 breeding pairs), discovered in 1983 on Manawatāwhi Three Kings Islands, remains genetically unknown, raising the possibility that it represents a unique evolutionary lineage with important taxonomic and conservation implications.
In this thesis I used 25,288 genome-wide single nucleotide polymorphisms (SNPs), generated through nuclear genotyping-by-sequencing, to assess population structure and genetic diversity in T. bulleri. A total of 85 individuals from three breeding colonies (Manawatāwhi: n = 5; Chatham Islands: n = 48; The Snares: n = 32) were analysed. The results showed no significant genetic differentiation between the Manawatāwhi, Chatham Islands (northern), and The Snares (southern) populations based on FST values of genetic differentiation (0.006-0.032). STRUCTURE analysis did not detect any population structure. However, principal component analysis (PCA) and a phylogenetic tree suggested some level of genetic structuring grouping Manawatāwhi and the northern population separate to the southern subspecies. These findings indicate weak genetic differentiation, likely shaped by historical connectivity and ongoing gene flow.
This study has uncovered the evolutionary history and the population genetic structuring of T. bulleri, providing genomic insights that can guide seabird conservation strategies to prevent further population decline and ensure the species’ long-term survival.