Marine Mammal Science最新文献

Harbor seals, as generalist predators, can adjust their diet in response to shifts in prey availability; thus, their diet composition has the potential to act as a biodiversity indicator. This study examined the diet of harbor seals in the Skagerrak by analyzing otoliths from scat samples collected in 2020 and compared species composition to historical datasets from 1977/78 and 1989. The diet in 2020 encompassed 28 fish species. Sandeel and Norway pout were the most common prey, comprising 39.6% and 21.8% of otoliths, respectively. The group haddock/pollack/saithe and ballan wrasse had the highest relative biomass contributions: 18.7% and 13.5%, respectively. A comparison with historical data revealed a shift in diet, with a notable decline in cod and herring consumption and an increase in sandeel and haddock/pollack/saithe. The findings suggest a dietary adaptation of harbor seals to available prey species. The reduced intake of energy-rich prey like herring raises concerns about whether current diet composition can meet the seals' energetic needs. The observed dietary changes may reflect changes in prey availability due to environmental and anthropogenic factors, emphasizing the importance of continued studies to assess the implications for harbor seal populations in the region.

The recovery of many cetacean species coincides spatially and temporally with intensifying anthropogenic threats. We undertook multi-year systematic surveys to quantify seasonal abundance and document the distribution of at-risk cetaceans, which is needed to assess the impacts of increasing human activities in the Canadian portions of the southern Salish Sea and Swiftsure Bank. We completed 21 line-transect surveys encompassing 5346 km of visual effort from September 2020 to December 2022 and collected 1514 sightings of five cetacean species using distance sampling protocols. Humpback whales, harbor porpoises, and Dall's porpoises were the most sighted species and were present in the area year-round, with strong seasonal differences in their abundance and distribution. Estimated abundance of humpback whales was lowest in winter at 17 (95% CI: 11–26) and highest in fall at 416 (261–663). Harbor porpoise abundance was also lowest during winter at 606 (366–1006) and highest in fall at 1415 (975–2055). Dall's porpoise abundance was lowest in summer at 65 (38–112) and highest in winter at 333 (224–494). These estimates were not corrected for availability or perception bias; thus, they may underestimate true abundance to some extent. These seasonal patterns in abundance and distribution will inform threat assessment and mitigation for cetaceans in this area of high and increasing vessel traffic.

We investigated Weddell seal (Leptonychotes weddellii) and leopard seal (Hydrurga leptonyx) vocalizations using passive acoustic monitoring beneath landfast ice and open water, 5.6 km seaward from Davis Station, East Antarctica. Eight-minute recordings were manually sampled at 1 h intervals over 24 h every 10 days from 24 July 2021 to 30 January 2022. Call counts for Weddell seals were highest in the winter, lower during the breeding season, and almost absent in the summer. This change coincided with the occurrence of open water over the recording site, a progressive shift in Weddell seal behavior from foraging to aggregating in local fjords for the annual pupping, mating, and molting periods, and an increase in leopard seal—a potential predator—call detection rates. Leopard seal calls were primarily detected in December after the landfast ice broke up. In winter, Weddell seal calling counts were highest at dusk and night, and lowest during the day when the seals may have been feeding. Neither species exhibited a diel calling pattern once there were 24 h of sunlight. Seal locations were associated with the presence and absence of landfast ice, and call detections were influenced by their distances to the recorder.

The Mediterranean common dolphin (Delphinus delphis) presents an enigmatic natural history during the past centuries. Widely prevalent in the 19th and early 20th centuries, it faced a significant decline across most of the basin by the late 1960s caused by multiple anthropogenic threats, including culling, bycatch, prey depletion, and habitat degradation. The IUCN has designated the Inner Mediterranean population of common dolphins as Endangered. Here, we analyzed stable isotopes of nitrogen and carbon (δ¹⁵N and δ¹³C) on skeletal remains collected in Mediterranean natural history museums to investigate spatio-temporal trophic shifts and niche partitioning of the Mediterranean common dolphin over the past 200 years. Results indicate that before the 1970s common dolphins occupied a higher trophic level, while after their population decline, they shifted their ecology, overlapping with the striped dolphin, reflecting changes in prey and habitat use. This study provides the first long-term evidence of trophic and ecological shifts in the Mediterranean common dolphin, offering insights into the potential drivers of its decline. Understanding these changes is crucial for conservation efforts, as the species' past and present ecological roles may inform strategies to mitigate further population losses.

The Shisiwani National Park (Anjouan, Comoros) is a cetacean biodiversity hotspot. However, the vocal behavior of marine mammals inhabiting the area has never been studied. In 2023, we conducted a 400-nautical-mile survey from a 5-m motorboat to determine their presence. Three dolphin species were encountered: the pantropical spotted dolphin (Stenella attenuata), the spinner dolphin (Stenella longirostris), and the melon-headed whale (Peponocephala electra). Dolphin vocalizations were recorded using a single hydrophone during each sighting. The visual inspection of spectrograms allowed the identification of 1495 whistles with a good signal-to-noise ratio. We extracted the frequency contour of each whistle and measured several spectrotemporal features employing the ROCCA module of PAMGUARD. Using a Random Forest algorithm, we classified whistles according to species, showing that while signals from non-congeneric species are distinguishable acoustically, those from congeneric species exhibit more subtle differences and are less so. Moreover, within the whistle repertoire of each species, we identified stereotyped frequency contours matching the SIGID criteria, possibly indicating the existence of signature whistles. Our study provides the first characterization of the whistles of three dolphin species in the Comoros archipelago and paves the way for developing the first fine-tuned tool for their Passive Acoustic Monitoring in these remote areas.

Genetic diversity and effective population size (N_e) are two key parameters involved in the long-term persistence of a population and, as such, are important metrics to assess the conservation status of a population (Frankham et al. 2010; Hoban et al. 2020; Lande and Shannon 1996). The population standing genetic variation (i.e., pre-existing genetic variation) is a basis for evolution and enables organisms to adapt to changing environmental conditions (Barrett and Schluter 2008; Frankham et al. 2010; Matuszewski et al. 2015; Reed and Frankham 2003). Furthermore, the risk of extinction of a population is greater for small effective population sizes, as it results in the loss of genetic diversity due to genetic drift and increases the risk of inbreeding depression (Gilpin and Soulé 1986; Hedrick and Kalinowski 2000; Kardos et al. 2023; Keller and Waller 2002). Events in the population demographic history, such as bottlenecks or founder events, can result in reductions of genetic diversity and in small effective population sizes (Allendorf et al. 2013; Garner et al. 2005). It has been estimated that an effective population size of at least 1000 effective breeders is required to ensure long-term persistence and sufficient adaptive potential for a given population, while an effective population size > 100 individuals should prevent negative effects due to inbreeding (Frankham 1995; Frankham et al. 2014).

The killer whale (Orcinus orca) is a cosmopolitan apex predator whose populations rarely include more than a few 100 individuals and, therefore, can be subject to erosion of genetic diversity and risks of extinction (Foote et al. 2023; Ford et al. 2018; Hoelzel et al. 2002; Kardos et al. 2023; Parsons et al. 2013). These populations can show large variation in their habitat, level of specialization in their feeding preferences and behavior, but also in their demographic trajectories and the types and levels of threats to which they are exposed (De Bruyn et al. 2013; Foote et al. 2016; Ford et al. 1998; Hoelzel et al. 2007; Jourdain et al. 2024; Morin et al. 2010; Riesch et al. 2012). In particular, over the past decades, some populations have greatly declined due to decreases in prey availability and/or negative interactions with humans (Beck et al. 2014; Ford et al. 2011, 2018; Guinet et al. 2015; Tixier et al. 2017), while others have shown significantly positive trends (Matkin et al. 2014; Towers et al. 2015).

Two morphologically, ecologically, and genetically distinct forms of