Marine Mammal Science最新文献

Foraging behavior is a key driver of ecological and evolutionary processes. Individual specialization can influence the behavioral flexibility of populations in response to environmental change, making it crucial to account for individual variation. While biologging has significantly advanced our understanding of individual specializations, its limitations in sample size and ethical concerns related to animal handling highlight the need for alternative approaches. We present a complementary, non-invasive method using relative vibrissae length (RVL) measured from images as a morphological proxy for foraging strategy in Galápagos sea lions (Zalophus wollebaeki). In this species, RVL differs significantly between strategies: benthic foragers have shorter vibrissae due to abrasion compared to pelagic foragers. Our method proved highly reliable, demonstrating strong intra- and inter-observer repeatability, as well as within-season consistency. Moreover, RVL remained stable across multiple years, indicating long-term persistence in individual foraging specialization. Vibrissae length exemplifies how behavioral specializations can shape morphological traits within an individual's lifetime, offering a novel approach to study ecological polymorphisms. Integrating RVL assessments with existing tracking methods can improve our ability to investigate foraging specializations at the population level and bridge the gap between high-resolution data and broader-scale ecological monitoring, providing a scalable tool for studying foraging strategies in pinnipeds.

Cetacean skin microbiome samples are traditionally collected by swabbing the skin of captured animals or using skin tissue from remote biopsies. The effects of different sampling methods are not well understood, and factors such as swab type and storage methods may affect the microbiome. The objective of this study was to determine if samples collected by swabbing biopsied skin from bottlenose dolphins yield sufficient microbial DNA for gene sequencing, while testing if commonly used sampling and storage methods affect the skin microbiome. Skin swab samples were collected during remote biopsy surveys with either a nylon flocked swab and flash frozen with liquid nitrogen or with a cotton swab and stored in RNAlater. Sequencing of the V3–V4 region of the 16S rRNA gene revealed swabs from dolphin skin biopsies yielded sufficient DNA to characterize the microbiome. We found no significant difference between the two sampling and storage methods tested, suggesting that studies using different techniques may be comparable. This work also demonstrates a novel technique to collect samples for interpretation of the skin microbiome of free-ranging animals. Benefits of this method are that it can be done without capture and preserves valuable and typically scarce biopsy skin samples for other analyses.

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.