Claire Garrigue

Marine megafauna species are affected by a wide range of anthropogenic threats. To evaluate the risk of such threats, species’ vulnerability to each threat must first be determined. We build on the existing threats classification scheme and ranking system of the International Union for Conservation of Nature (IUCN) Red List of Threatened Species by assessing the vulnerability of 256 marine megafauna species to 23 at‐sea threats. The threats we considered included individual fishing gear types, climate‐change‐related subthreats not previously assessed, and threats associated with coastal impacts and maritime disturbances. Our ratings resulted in 70 species having high vulnerability ( v > 0.778 out of 1) to at least 1 threat, primarily drifting longlines, temperature extremes, or fixed gear. These 3 threats were also considered to have the most severe effects (i.e., steepest population declines). Overall, temperature extremes and plastics and other solid waste were rated as affecting the largest proportion of populations. Penguins, pinnipeds, and polar bears had the highest vulnerability to temperature extremes. Bony fishes had the highest vulnerability to drifting longlines and plastics and other solid waste; pelagic cetaceans to 4 maritime disturbance threats; elasmobranchs to 5 fishing threats; and flying birds to drifting longlines and 2 maritime disturbance threats. Sirenians and turtles had the highest vulnerability to at least one threat from all 4 categories. Despite not necessarily having severe effects for most taxonomic groups, temperature extremes were rated among the top threats for all taxa except bony fishes. The vulnerability scores we provide are an important first step in estimating the risk of threats to marine megafauna. Importantly, they help differentiate scope from severity, which is key to identifying threats that should be prioritized for mitigation.

Context: Historically, humpback whales migrating past Aotearoa New Zealand (NZ) were linked to western South Pacific wintering grounds and Antarctic feeding grounds. As populations have recovered, research has focused on contemporary connectivity patterns throughout the South Pacific. Aims: To determine the contemporary connectivity of winter breeding grounds for humpback whales on their northern and southern migrations past NZ, and those at the Kermadec Islands (Rangitāhua) migratory stopover. Methods: We generated DNA profiles (mitochondrial DNA (mtDNA) haplotypes, genetic sex and microsatellite genotypes) using skin samples collected from whales between 1998 and 2021. We used comparisons of DNA profiles and a mixed-stock analysis of mtDNA haplotypes to determine the most likely wintering grounds of genetically identified individuals. Key results: DNA profiles of 350 individual whales from NZ were compared to profiles from Oceania (n > 2000), Central and South America (n = 452) and East Australia (n = 809). This comparison revealed 35 genotype matches, mainly to New Caledonia and East Australia. The mixed-stock analysis showed that northbound whales (n = 145) had approximately equal assignment proportions to East Australia and New Caledonia whereas southbound whales (n = 74) showed a two-fold higher assignment to East Australia. In contrast, whales passing Rangitāhua (n = 112) assigned to New Caledonia and other Pacific wintering grounds but not to East Australia. Conclusions: Humpback whales passing mainland NZ on their north and southbound migrations are strongly associated with East Australia and New Caledonia wintering grounds. Those migrating south past Rangitāhua have a broader range of wintering ground destinations, including a connection to Central America.

The recent Kunming-Montreal Global Biodiversity Framework (GBF) sets ambitious goals but no clear pathway for how zero loss of important biodiversity areas and halting human-induced extinction of threatened species will be achieved. We assembled a multi-taxa tracking dataset (11 million geopositions from 15,845 tracked individuals across 121 species) to provide a global assessment of space use of highly mobile marine megafauna, showing that 63% of the area that they cover is used 80% of the time as important migratory corridors or residence areas. The GBF 30% threshold (Target 3) will be insufficient for marine megafauna’s effective conservation, leaving important areas exposed to major anthropogenic threats. Coupling area protection with mitigation strategies (e.g., fishing regulation, wildlife-traffic separation) will be essential to reach international goals and conserve biodiversity.

Humpback whale song is a culturally transmitted behavior. Human language, which is also culturally transmitted, has statistically coherent parts whose frequency distribution follows a power law. These properties facilitate learning and may therefore arise because of their contribution to the faithful transmission of language over multiple cultural generations. If so, we would expect to find them in other culturally transmitted systems. In this study, we applied methods based on infant speech segmentation to 8 years of humpback recordings, uncovering in whale song the same statistical structure that is a hallmark of human language. This commonality, in two evolutionarily distant species, points to the role of learning and cultural transmission in the emergence of properties thought to be unique to human language.

Variation in reproductive success is a fundamental prerequisite for sexual selection to act upon a trait. Assessing such variation is crucial in understanding a species’ mating system and offers insights into population growth. Parentage analyses in cetaceans are rare, and the underlying forces of sexual selection acting on their mating behaviours remain poorly understood. Here, we combined 25 years of photo-identification and genetic data to assess patterns of male reproductive success and reproductive autonomy of the New Caledonian (Oceania, South Pacific) humpback whale breeding population. Paternity analysis of 177 mother–offspring pairs and 936 males revealed low variation in male reproductive success (average 1.17 offspring per father) relative to other polygynous species. The observed skew in success was higher than expected under random mating and skewed overall towards males (93%) without evidence of paternity over the study period. Finally, an updated male gametic mark-recapture abundance estimate of 2084 (95% confidence interval = 1761–2407, 1995–2019) fell between previous census estimates of the New Caledonian population and the wider Oceanian metapopulation. Our results provide critical insights into the mating competition of male humpback whales and population dynamics across Oceanian populations, two important factors affecting the slow recovery from whaling across the South Pacific region.

How animals navigate during long-distance migration remains a mystery. Many theories have been proposed¹ (Keeton, 1979), with the Earth’s magnetic field emerging as a clear potential source of orientational information for navigational decision-making across diverse taxa² (Putman, 2022). Yet, the mechanics involved in magnetic navigation remain unknown³ (Schneider et al., 2023). Globally distributed records available from historic whaling^4-5 (AOWLD, 2023; Yablokov et al., 1998) in combination with modern satellite-tracking datasets⁶ (Horton et al., 2022) for baleen whales create a unique opportunity to illuminate the mechanics of cetacean navigation. Here, we show that baleen whale migratory destinations over the last >200 years are systematically distributed in horizontal plane magnetic coordinates. Specifically, blue (Balaenoptera musculus), bowhead (Balaena mysticetus), fin (Balaenoptera physalus), gray (Eschrichtius robustus), humpback (Megaptera novaeangliae), and right (Eubalaena spp.) whales non-randomly inhabit areas where magnetic declination (MD) closely approximates integer and half-integer multiples of the Earth’s 23.44° axial tilt. Our findings, which are highly reproducible through both space and time, demonstrate that baleen whale navigation between seasonal habitats occurs via the integration of magnetic and astronomic orientation cues³. By referencing MD values to the rise and set azimuths of the Sun, baleen whale movements define mechanistic horizontal plane heliomagnetic coordinate trajectories across all ocean basins.

The major histocompatibility complex (MHC) is a highly polymorphic gene family that is crucial in immunity, and its diversity can be effectively used as a fitness marker for populations. Despite this, MHC remains poorly characterised in non‐model species (e.g., cetaceans: whales, dolphins and porpoises) as high gene copy number variation, especially in the fast‐evolving class I region, makes analyses of genomic sequences difficult. To date, only small sections of class I and IIa genes have been used to assess functional diversity in cetacean populations. Here, we undertook a systematic characterisation of the MHC class I and IIa regions in available cetacean genomes. We extracted full‐length gene sequences to design pan‐cetacean primers that amplified the complete exon 2 from MHC class I and IIa genes in one combined sequencing panel. We validated this panel in 19 cetacean species and described 354 alleles for both classes. Furthermore, we identified likely assembly artefacts for many MHC class I assemblies based on the presence of class I genes in the amplicon data compared to missing genes from genomes. Finally, we investigated MHC diversity using the panel in 25 humpback and 30 southern right whales, including four paternity trios for humpback whales. This revealed copy‐number variable class I haplotypes in humpback whales, which is likely a common phenomenon across cetaceans. These MHC alleles will form the basis for a cetacean branch of the Immuno‐Polymorphism Database (IPD‐MHC), a curated resource intended to aid in the systematic compilation of MHC alleles across several species, to support conservation initiatives.

Context: The dynamic habitat use by dugongs (Dugong dugon) in small coral reef lagoon systems spatially limited by tides is not well understood and has hampered adaptive management. Aims: We investigated how dugongs locally used a high conservation value coral-reef lagoon system during different seasons and tides to support local management. Methods: We conducted local-scale aerial surveys to document the seasonal and tidal changes in the distribution and number of dugongs over seagrass and non-seagrass coral reef habitats in a small lagoon in New Caledonia. The surveys were conducted fortnightly over 18 months in different seasons and at different tides. Temperature loggers and existing local footage of dugong herding behaviour were used to study the habitat use and behaviour of the animals in the area. Key results: More dugongs were sighted in Cap Goulvain during the cool season than during the warm season. As tides restricted access to the intertidal seagrass meadows and during the cool season, more dugongs were sighted outside the lagoon on the fore reef shelf outside the lagoon. Dugongs were resting in large aggregations during their use of this non-seagrass habitat. Conclusions: Our study emphasises the importance of non-seagrass habitats for dugongs in spatially restricted coral reef environments as well as the importance of considering outer lagoon habitats as key dugong management areas. This study also adds evidence of behavioural thermoregulation in dugongs. Implications: The development of dynamic management strategies is essential, especially where different habitats should be protected at different times of the year.

The field of marine mammal conservation has dramatically benefited from the rapid advancement of methods to assess the reproductive physiology of individuals and populations from steroid hormones isolated from minimally invasive skin–blubber biopsy samples. Historically, this vital information was only available from complete anatomical and physiological investigations of samples collected during commercial or indigenous whaling. Humpback whales (Megaptera novaeangliae) are a migratory, cosmopolitan species that reproduce in warm, low-latitude breeding grounds. New Caledonia is seasonally visited by a small breeding sub-stock of humpback whales, forming part of the endangered Oceania subpopulation. To better understand the demographic and seasonal patterns of reproductive physiology in humpback whales, we quantified baseline measurements of reproductive hormones (progesterone—P4, testosterone—T and 17β-estradiol—E2) using an extensive archive of skin–blubber biopsy samples collected from female humpback whales in New Caledonia waters between 2016 and 2019 (n = 194). We observed significant differences in the P4, T and E2 concentrations across different demographic groups of female humpback whales, and we described some of the first evidence of the endocrine patterns of estrous in live free-ranging baleen whales. This study is fundamental in its methodological approach to a wild species that has a global distribution, with seasonally distinct life histories. This information will assist in monitoring, managing and conserving this population as global ecological changes continue to occur unhindered.