Marine Mammal Science最新文献

Baleen plates have been widely used to investigate the life cycle of mysticetes using a variety of chemical markers. Among these, stable isotope analysis (SIA) has been consistently applied to investigate their migratory movements and shifts in diet. However, the location of the baleen segment reflecting the most recently incorporated stable isotopes, corresponding to the whale's most contemporary habitat and diet composition, remains unclear and hampers the correct interpretation of the results. In this study, we analyzed δ¹⁵N, δ¹³C, and δ³⁴S values along the baleen plate of a pregnant fin whale (Balaenoptera physalus) and its fetus to identify the baleen segment/s that were simultaneously deposited in both individuals. Our approach was based on the premise that the fetal baleen had been synthesized soon before sampling and therefore reflected contemporary habitat and diet signals of the pregnant whale. To allow comparison, the results were corrected for fetal–mother discrimination (F-MD) factors (i.e., the isotopic differences between fetal and maternal tissues). Fetal δ¹⁵N and δ¹³C values aligned most closely with maternal baleen segments located 2–4 cm below the gingiva line, indicating that they had likely been deposited simultaneously with fetal baleen formation and therefore reflect the pregnant whale's most recent diet and habitat use. Conversely, fetal δ³⁴S values did not consistently align with any maternal baleen segments, probably due to dissimilar incorporation rates and/or differences in tissue discrimination factors. Our results highlight the importance of extracting baleen from its base, below the gingival line, to correctly assign the timing of deposition of the various baleen segments and ensure accurate interpretation in chronological studies using intrinsic markers on baleen plates.

Although the eastern North Pacific gray whale (Eschrichtius robustus) population has recovered from population declines associated with whaling, they are closely monitored, especially in association with Unusual Mortality Events. Metrics to improve assessment of the health of individual animals, when averaged, are valuable to inform monitoring and management. We used 30 years of photographic data of a unique gray whale feeding aggregation to develop and test a new methodology for assessing body condition. This group of individuals (20 as of 2021, but 11 in the study group), known as the Sounders, regularly enter Puget Sound, Washington, USA, to forage on ghost shrimp in the spring and early summer. Almost 35,000 images were examined and 729 were selected as being suitable to assess individual body condition. Geometric measuring tools in open-source image analysis software were used to measure a novel body condition angle, °BC, as a proxy for changes in blubber thickness. This °BC varied significantly with the day of the year, with increases in blubber thickness observed as individuals progressed through the feeding season. Other metrics, such as year and surfacing interval, were not found to have a significant effect on °BC within this dataset. This novel index of body condition illustrates the opportunity to develop new methods to quantitatively assess change in individuals at both seasonal and annual scales. Expansion of this method to the larger eastern North Pacific gray whale population may allow for a more detailed examination of fluctuations in body condition to better understand both environmental and anthropogenic impacts. There is also potential for adaptation of the method to apply to historic photo catalogs of other baleen whale species, creating opportunities for enhanced data-driven management plans.

Marine vessel traffic is a significant contributor to anthropogenic noise pollution and a source of disturbance for many marine species. It is important to assess the impact of vessel visitation and the number of potential disturbance events at sensitive marine sites to ensure management strategies are adequate. This study integrated passive acoustic monitoring (PAM), direct visual observation, and vessel traffic data to monitor vessel visitation at Seal Rocks, the largest Australian fur seal (Arctocephalus pusillus doriferus) breeding colony and site with the least stringent vessel approach limits. Vessel visitation was compared between the assumed low (off-peak) and high (peak) visitation seasons. Visual observations were also used to map visitation around the colony and determine breaches of approach regulations. Vessel visitation and the associated noise were significantly higher in the peak season and direct visual observations showed that breaches of approach regulations were common (32%), highlighting the need for improved education and enforcement of compliance at the site. This study provides important context for assessing the impact of vessel noise and visitation at Seal Rocks and can be applied to conservation and management strategies at this and other sensitive marine sites.

Fraser's dolphin (Lagenodelphis hosei) remains poorly studied due to its elusive behavior, rarity, and preference for deep offshore habitats. While dolphins use frequency-modulated whistles for communication, detailed acoustic descriptions exist for only a few species. This study provides the first comprehensive characterization of Fraser's dolphin whistle acoustic structure and repertoire, based on recordings from eight groups (15–300 individuals) collected during boat-based surveys at three sites in the Lesser Antilles. A total of 2999 whistles were analyzed for acoustic structure, with 1802 contours and a subsample of 728 whistles (weighted by group size) categorized using Beluga and ARTwarp to estimate repertoire size and composition. Whistles exhibited a broader frequency range (1.12–31.40 kHz) than previously reported. Acoustic overlap across sites supports the hypothesis of a proposed single population in the region. The repertoire was comprised of 298 whistle types, predominantly upsweeps and sine contours. Whistle type richness (q = 0) did not plateau, indicating incomplete sampling of rare types, whereas Shannon (q = 1) and Simpson (q = 2) diversity did plateau, suggesting that the most produced whistle types were well represented in this study. These findings offer a detailed baseline of Fraser's dolphin whistle repertoire and contribute to the development of species-specific detectors for passive acoustic monitoring, as well as future research on geographic variation, social communication, and responses to environmental and anthropogenic changes.

Age is an important parameter to understand species life-history characteristics. Recently, DNA methylation methods have emerged as innovative tools to estimate the age of marine mammals. Narwhal (Monodon monoceros) epigenetic age estimates were computed using beluga (Delphinapterus leucas), killer whale (Orcinus orca), bowhead (Balaena mysticetus), odontocete, cetacean, and mammalian epigenetic clocks and were compared with age estimates from counting growth layer groups in tusks (n = 7) and/or aspartic acid racemization of eye lenses (n = 25). Pearson's correlation coefficients (R) ranged 0.68–0.87 for the clocks, but the absolute accuracy of age estimates was quite low, with median absolute error (MAE) between epigenetic and reference age ranging 7–37.5 years. To address this lack of accuracy, we more broadly investigated DNA methylation levels at cytosine-guanine sites (CpGs) for this same set of aged narwhals to develop a narwhal-specific epigenetic clock. Using a penalized regression model on 1009 CpG sites, ten CpGs (plus intercept) were selected, resulting in a model with a R = 0.70 and MAE of 8.6 years. This is the first study to age narwhals using DNA methylation patterns and to develop a narwhal-specific epigenetic aging clock, which will assist with understanding important life-history characteristics for sustainable conservation management.

Large “super-groups” of feeding humpback whales (Megaptera novaeangliae) have occurred regularly off the West Coast of South Africa since ca. 2011, but little is known about their feeding behavior. We used opportunistic underwater video footage to investigate near-surface lunge feeding behavior, group coordination, and the use of pectoral fins in feeding. We analyzed 113 min of underwater video footage collected over 6 days. Whales passed through the frame on 623 occasions and were seen actively lunging on 182 occasions. No lateralization or coordinated foraging was observed. Gape cycles were short (mean mouth opening phase: 2.38 s and mouth closing: 1.69 s) with buccal pouch draining lasting the longest (15.61 s) and being a mostly passive action. The whales often surfaced while the pouch still contained water. Lunges and draining took place in all directions but mostly at ascending and even near vertical angles. Active flipper movements were observed during 81% of feeding lunges, providing further evidence that these uniquely large appendages are used hydrodynamically when feeding and may also play a role in prey herding. Disruption of feeding by diver presence was low. This study provides novel insight into the feeding behavior of Southern Hemisphere humpback whale super-groups, and potential human-whale interactions.