Variation in blubber cortisol levels in a recovering humpback whale population inhabiting a rapidly changing environment

Effectiveness of marine protected areas in safeguarding important migratory megafauna habitat

Marine protected areas (MPAs) are a commonly used management tool to safeguard marine life from anthropogenic impacts, yet their efficacy often remains untested. Evaluating how highly dynamic marine species use static MPAs is challenging but becoming more feasible with the advancement of telemetry data. Here, we focus on southern right whales (Eubalaena australis, SRWs) in the waters off Aotearoa/New Zealand, which declined from 30,000 whales to fewer than 40 mature females due to whaling. Now numbering in the low thousands, the key socializing and nursery areas for this population in the remote subantarctic islands are under the protection of different types of MPAs. However, the effectiveness of these MPAs in encompassing important whale habitat and protecting the whales from vessel traffic has not been investigated. To address this, we analyzed telemetry data from 29 SRWs tagged at the Auckland Islands between 2009 and 2022. We identified two previously unknown and currently unprotected areas that were used by the whales for important behaviors such as foraging, socializing, or resting. Additionally, by combining whale locations and vessel tracking data (2020-2022) during peak breeding period (June to October), we found high spatiotemporal overlap between whales and vessels within several MPAs, suggesting the whales could still be vulnerable to multiple anthropogenic stressors even when within areas designated for protection. Our results identify areas to be prioritized for future monitoring and investigation to support the ongoing recovery of this SRW population, as well as highlight the overarching importance of assessing MPA effectiveness post-implementation, especially in a changing climate.

Blubber gene expression and cortisol concentrations reveal changing physiological stress in a Southern ocean sentinel species

The health of migratory eastern Australian humpback whales (Megaptera novaeangliae) can reflect the condition of their remote polar foraging environments. This study used gene expression (LEP, LEPR, ADIQ, AhR, TNF-α, HSP-70), blubber hormone concentrations (cortisol, testosterone), and photogrammetric body condition to assess this sentinel species during a period of unprecedented changes to anthropogenic activity and natural processes. The results revealed higher cortisol concentrations in 2020 compared to 2021, suggesting a decline in physiological stress between years. Additionally, metabolic transcripts LEPR, and AhR, which is also linked to xenobiotic metabolism, were upregulated during the 2020 southbound migration. These differences suggest that one or more environmental stressors were reduced between 2020 and 2021, with upregulated AhR possibly indicating a Southern Ocean pollutant declined between the years. This research confirms a Southern Ocean-wide decrease in whale stress during the study period and informs efforts to identify key stressors on Antarctic marine ecosystems.

No distinct local cuisines among humpback whales: A population diet comparison in the Southern Hemisphere

Southern hemisphere humpback whale (Megaptera novaeangliae, SHHW) breeding populations follow a high-fidelity Antarctic krill (Euphausia superba) diet while feeding in distinct sectors of the Southern Ocean. Their capital breeding life history requires predictable ecosystem productivity to fuel migration and migration-related behaviours. It is therefore postulated that populations feeding in areas subject to the strongest climate change impacts are more likely to show the first signs of a departure from a high-fidelity krill diet. We tested this hypothesis by investigating blubber fatty acid profiles and skin stable isotopes obtained from five SHHW populations in 2019, and comparing them to Antarctic krill stable isotopes sampled in three SHHW feeding areas in the Southern Ocean in 2019. Fatty acid profiles and δ13C and δ15N varied significantly among all five populations, however, calculated trophic positions did not (2.7 to 3.1). Similarly, fatty acid ratios, 16:1ω7c/16:0 and 20:5ω3/22:6ω3 were above 1, showing that whales from all five populations are secondary heterotrophs following an omnivorous diet with a diatom-origin. Thus, evidence for a potential departure from a high-fidelity Antarctic krill diet was not seen in any population. δ13C of all populations were similar to δ13C of krill sampled in productive upwelling areas or the marginal sea-ice zone. Consistency in trophic position and diet origin but significant fatty acid and stable isotope differences demonstrate that the observed variability arises at lower trophic levels. Our results indicate that, at present, there is no evidence of a divergence from a high-fidelity krill diet. Nevertheless, the characteristic isotopic signal of whales feeding in productive upwelling areas, or in the marginal sea-ice zone, implies that future cryosphere reductions could impact their feeding ecology.

Association of seasonal changes in circulating cortisol concentrations with the expression of cortisol biosynthetic enzymes and a glucocorticoid receptor in the blubber of common bottlenose dolphin

Cortisol is secreted from the adrenal cortex in response to stress, and its circulating levels are used as robust physiological indicators of stress intensity in various animals. Cortisol is also produced locally in adipose tissue by the conversion of steroid hormones such as cortisone, which is related to fat accumulation. Circulating cortisol levels, probably induced by cold stress, increase in cetaceans under cold conditions. However, whether cortisol production in subcutaneous adipose tissue is enhanced when fat accumulation is renewed during the cold season remains unclear. Therefore, in this study, we examine the effect of environmental temperature on the expression of cortisol synthesis-related enzymes and a glucocorticoid receptor in the subcutaneous fat (blubber) and explore the association between these expressions and fluctuations in circulating cortisol levels in common bottlenose dolphins (Tursiops truncatus). Skin biopsies were obtained seasonally from eight female dolphins, and seasonal differences in the expression of target genes in the blubber were analyzed. Blood samples were collected throughout the year, and cortisol levels were measured. We found that the expressions of cytochrome P450 family 21 subfamily A member 2 (CYP21A2) and nuclear receptor subfamily 3 group C member 1 (NR3C1), a glucocorticoid receptor, were increased in the cold season, and 11 beta-hydroxysteroid dehydrogenase type 1 (HSD11B1) showed a similar trend. Blood cortisol levels increased when the water temperature decreased. These results suggest that the conversion of 17-hydroxyprogesterone to cortisol via 11-deoxycortisol and/or of cortisone to cortisol is enhanced under cold conditions, and the physiological effects of cortisol in subcutaneous adipose tissue may contribute to on-site lipid accumulation and increase the circulating cortisol concentrations. The results obtained in this study highlight the role of cortisol in the regulation of the blubber that has developed to adapt to aquatic life.

Descriptions and patterns in opportunistic marine debris collected near Palmer Station, Antarctica

Observations of marine debris in Antarctica have been increasing; however, impacts, distributions, sources, and transport pathways of debris remain poorly understood. Here, we describe the spatial distribution, types, and potential origins of marine debris in 2022/2023 near Palmer Station, Antarctica. We opportunistically collected 135 pieces of marine debris with the majority of items found along shorelines (90 %), some found in/near seabird nests/colonies (7 %) and few on inland rocky terrain (3 %). Plastic and abandoned, lost, or discarded fishing gear dominated observed debris. Results suggest that wind and the Antarctic Coastal Current may be a major pathway for debris. This study is the first assessment of marine debris in this region and suggests that oceanography, weather patterns, and shoreline geomorphology could play a role in determining where debris will accumulate. Continued tracking of debris and development of structured surveys is important for understanding the impacts of human activities in a biological hotspot.

Assessing variation in faecal glucocorticoid concentrations in gray whales exposed to anthropogenic stressors

Understanding how individual animals respond to stressors behaviourally and physiologically is a critical step towards quantifying long-term population consequences and informing management efforts. Glucocorticoid (GC) metabolite accumulation in various matrices provides an integrated measure of adrenal activation in baleen whales and could thus be used to investigate physiological changes following exposure to stressors. In this study, we measured GC concentrations in faecal samples of Pacific Coast Feeding Group (PCFG) gray whales (Eschrichtius robustus) collected over seven consecutive years to assess the association between GC content and metrics of exposure to sound levels and vessel traffic at different temporal scales, while controlling for contextual variables such as sex, reproductive status, age, body condition, year, time of year and location. We develop a Bayesian Generalized Additive Modelling approach that accommodates the many complexities of these data, including non-linear variation in hormone concentrations, missing covariate values, repeated samples, sampling variability and some hormone concentrations below the limit of detection. Estimated relationships showed large variability, but emerging patterns indicate a strong context-dependency of physiological variation, depending on sex, body condition and proximity to a port. Our results highlight the need to control for baseline hormone variation related to context, which otherwise can obscure the functional relationship between faecal GCs and stressor exposure. Therefore, extensive data collection to determine sources of baseline variation in well-studied populations, such as PCFG gray whales, could shed light on cetacean stress physiology and be used to extend applicability to less-well-studied taxa. GC analyses may offer greatest utility when employed as part of a suite of markers that, in aggregate, provide a multivariate measure of physiological status, better informing estimates of individuals' health and ultimately the consequences of anthropogenic stressors on populations.