Marine Mammal Science最新文献

Anthropogenic activities can alter the occurrence of many animal species, and marine mammals, in particular, may be impacted by coastal development. The marine otter, Lontra felina, inhabits the coasts of southern South America, where increasing urban encroachment and extractive activities are progressively altering its habitat. We estimated the abundance of L. felina at six study sites (with similar habitat structure) in northern Chile over three years, relating this to the presence of people, boats, and pets. We also calculated a human disturbance index using these human presence variables. Our findings indicated that marine otter abundance was negatively associated with the number of people, while boats and pets showed no significant associations with otter abundance. The human disturbance index, which integrates these variables, was also negatively related to otter abundance. Although marine otters are generally considered tolerant to human presence in coastal environments, our results show a consistent pattern of lower otter abundance at sites with greater human presence, particularly where people directly accessed shoreline habitats. This pattern is not explained by habitat structure, which was similar across sites, and suggests that local human activity may contribute to shaping spatial variation in abundance. This multi-year assessment raises a warning about human influence on native species in coastal areas, which can inform evidence-based conservation decisions.

In the North Pacific, there are at least three genetically different ecotypes of killer whales (Orcinus orca), referred to as resident, offshore, and transient. A previous study suggested that killer whales around Hokkaido belong to fish-eating (resident and/or offshore ecotypes) and mammal-eating (transient ecotype) groups. These results were supported by haplotypes based on the combination of 1193 bp of cytochrome b and 420 bp of the control region in mitochondrial genomes. However, this analysis was not sufficient to discriminate between resident and offshore ecotypes because of the short sequence lengths. In this study, we analyzed whole mitochondrial genomes of 25 killer whales sampled around Hokkaido to clarify the ecotypes and mitochondrial genome haplotypes. Phylogenetic analysis revealed the presence of resident and transient ecotypes around Hokkaido. The whales identified as residents shared an identical haplotype, which is the most common haplotype in the western North Pacific. In contrast, the transients around Hokkaido exhibited eight haplotypes, including seven novel ones among the 19 individuals, and their haplotype richness was the highest among the North Pacific populations. This result suggests that the Hokkaido coast served as a refugium for transient killer whales during the Last Glacial Maximum.

Rice's whale (Balaenoptera ricei), recently classified as a species distinct from Bryde's whales, exemplifies the challenges in cetacean taxonomy arising from limited morphological divergence and an overreliance on restricted genetic datasets. Darwin's principle, that species represent “dominant varieties” within a continuum, underscores the inherent subjectivity in such taxonomic judgments. Genetic analyses based on mitochondrial DNA (mtDNA) haplotypes identify Rice's whale as a monophyletic lineage, yet its pronounced genetic homogeneity may reflect recent demographic bottlenecks, possibly caused by historical whaling, rather than deep evolutionary isolation. Morphological differentiation, although subtle, includes cranial features primarily involving nasal bones. Ecologically, Rice's whales occupy a restricted range in the northeastern Gulf of Mexico, potentially representing a relict population that was historically more widespread before commercial whaling. Comparative cases, such as North Atlantic right whales and northern elephant seals, illustrate how severe population reductions can rapidly produce distinct genetic profiles. The issue is not the use of genetic evidence itself but its interpretation: genetic diagnosability, particularly when based on limited mtDNA data, is not equivalent to speciation and may simply reflect restricted gene flow or recent isolation without reproductive or ecological divergence. Recognizing Rice's whale as a species thus highlights the tension between taxonomy based primarily on molecular diagnosability and a more integrative approach, emphasizing the need for multiple, concordant lines of evidence before assigning full species status.

Foraging behavior and success are a function of prey abundance and distribution in marine environments. Oceanographic processes shape prey spatial structuring, leading to some areas of high heterogeneity and others of high homogeneity, causing marine predators to exhibit different at-sea behaviors. Our study investigated foraging success and effort of adult female southern elephant seals dispersing west or east of the Kerguelen Plateau. We quantified drift dive data and dive metric data for 153 seals, focusing on timing and spatial patterns in seal buoyancy change and its relationship with seal dive behavior. We assessed whether differences were linked to differing responses to forage quality. Overall, buoyancy changes indicated elephant seals had similar foraging success in both homogeneous (west) and heterogeneous (east) environments around the Kerguelen Plateau. Seals to the east dived deeper, with shorter hunting times and higher descent rates, probably related to higher mesoscale activity, while those to the west had lower descent rates and focused on shallower prey. Both groups responded to changes in forage quality by increasing ascent/descent rate in high-quality areas. These results suggest that these seals behave as predicted by the marginal value theorem and in so doing adapt foraging behavior to efficiently exploit profitable prey patches.