Marine Mammal Science最新文献

Maritime traffic is a major contributor of anthropogenic disturbance for cetaceans, especially for coastal populations, such as that of resident common bottlenose dolphins (Tursiops truncatus) in the Sado estuary (Portugal). Animals have been found to adjust their vocal behavior by changing vocal rates, or call frequency and/or duration, to overcome masking effects of underwater noise. To evaluate the potential impacts of boat traffic on the acoustic behavior of these dolphins, emission rates and acoustic characteristics of whistles and burst-pulsed signals were analyzed with and without boats operating nearby. In this study, no significant differences were found for emission rates of each type of vocal element in the presence of vessels. However, significant differences were found in acoustic parameters, namely changes in frequency and duration, for whistles and for pulsed sounds (creaks, grunts, squeaks, and gulps). These changes, such as a shift in vocal frequencies and production of shorter signals, may represent behavioral strategies to compensate for the noisy environment. Although resident bottlenose dolphins in the Sado region seem to have developed some tolerance to vessel noise, continuous noise exposure and noise-induced frequency shifts in vocal outputs could have indirect fitness costs for this population.

We introduce a semiautomated machine learning method that employs high-resolution imagery for the species-level classification of Antarctic pack-ice seals. By incorporating the spatial distribution of hauled-out seals on ice into our analytical framework, we significantly enhance the accuracy of species identification. Employing a Random Forest model, we achieved 97.4% accuracy for crabeater seals and 98.0% for Weddell seals. To further refine our classification, we included three linearity measures: mean distance to a group's regression line, straightness index, and sinuosity index. Additional variables, such as the number of neighboring seals within a 250 m radius and distance of individual seals to the sea ice edge, also contributed to improved accuracy. Our study marks a significant advancement in the development of a cost-effective, unified Antarctic seal monitoring system, enhancing our understanding of seal spatial behavior and enabling more effective population tracking amid environmental changes.

The use of acoustic signals to communicate is widespread among marine mammals and vocalizations are involved in all their social interactions. Due to many factors, acoustic features of a species' vocalizations may differ among populations. The present study investigated both micro- and macro-geographical variation in the vocalizations of Cape fur seal females, males, and pups. Acoustic measurements were performed on calls recorded at four South African and two Namibian sites (maximum range ~ 1,000 km). Comparisons among close sites in South Africa revealed no micro-geographical variation (maximum range ~130 km) in females' and pups' vocalizations. Barks of subadult males had different features among sites, which may be explained mostly by the context of call production. At the macro-geographical scale (South Africa vs. Namibia), all call types varied significantly among sites. Several extrinsic and intrinsic factors were suggested to drive such differences. For females' and pups' calls, differences might be explained by environmental factors, whereas for males' barks, behavioral differences are the most likely explanation for acoustic differences (breeding vs. resting sites). Such investigations help understand how acoustic communication in marine mammals is shaped by ecological drivers.

Image processing using traditional photogrammetric methods is a labor-intensive process. The collection of photogrammetry images during aerial surveys is expanding rapidly, creating new challenges to analyze images promptly and efficiently, while reducing human error during processing. Computer vision-assisted photogrammetry, a field of artificial intelligence (AI), can automate image processing, greatly enhancing the efficiency of photogrammetry. Here, we present a practical and efficient program capable of automatically extracting the fine-scale photogrammetry of East Asian finless porpoises (Neophocaena asiaeorientalis sunameri). Our results indicated that computer vision-assisted photogrammetry could achieve the same accuracy as traditional photogrammetry, and the results of the comparisons were validated against the direct measurements. Three-dimensional (3D) models using computer vision-assisted photogrammetric morphometrics generated trustworthy body volume estimates. We also explored the one image-based 3D modeling technique, which is less accurate, but still useful when only one image of the animal is available. Although several limitations exist in the current program, improvements could be made to narrow the virtual-reality gap when more images are available for machine learning and training. We recommend this program for analyzing images of marine mammals possessing a similar morphological contour.

The establishment of marine protected areas (MPAs) for cetaceans is an important strategy to mitigate human disturbance and protect biodiversity. Despite abundant cetacean species, there are only a few MPAs dedicated to cetacean conservation in China, all of which are for inshore dolphins. Bryde's whales, the only nearshore baleen whale population in mainland China, are conflicting with intensive human activities, yet an effective conservation strategy is lacking. This study used species distribution models to analyze distribution patterns and suitable habitats of Bryde's whales in the Beibu Gulf and proposes the first baleen whale MPA in China. Our results showed Bryde's whales have a seasonal distribution pattern in the Beibu Gulf, and that the waters around Weizhou Island and the southeastern coast of Vietnam were their core habitats. The seasonal nighttime light data indicated a negative relationship between the number of ship lights and Bryde's whale sightings and suggest that Bryde's whales might be threatened by fisheries. We proposed an MPA based on the results, suggesting that the waters within 20 km around Weizhou Island should be declared a protected area. Furthermore, we recommend that anthropogenic activities in the waters around Weizhou Island are better managed to reduce negative impacts on marine life.

Visual line-transect surveys are widely used to estimate the abundance of cetacean populations; however, this method can be prohibitively expensive. Thus, a less expensive alternative method was investigated in the present study, i.e., whether temporal changes in the bycatch per unit effort (BPUE) of cetaceans could be used to index the changes in their abundance. Specifically, the relationship between the annual BPUE of two main bycatch fisheries and the relative abundance of common dolphins (Delphinus delphis) was examined in 2012, 2013, 2015, and 2017 when vessel-based line-transect surveys were conducted in the coastal region of the East Sea of Korea. The encounter rate (individuals/km) by study year was significantly correlated with the annual BPUE of set nets. An increase in the density (individuals/km²) of common dolphins, estimated according to a hazard-rate key function by study year, was associated with an increase in the BPUE of set nets. These results suggest that the annual BPUE of common dolphins could be used to index the species' relative abundance. The BPUE of set nets, which are fixed in coastal regions, reflect the densities of common dolphins in the coastal regions better than that of gill nets used in coastal and offshore regions.