Humpback whale song recordings suggest common feeding ground occupation by multiple populations

Humpback whale males are known to sing on their low-latitude breeding grounds, but it is well established that songs are also commonly produced ‘off-season’ on the feeding grounds or during migration. This opens exciting opportunities to investigate migratory aggregations, study humpback whale behavioral plasticity and potentially even assign individual singers to specific breeding grounds. In this study, we analyzed passive acoustic data from 13 recording positions and multiple years (2011–2018) within the Atlantic sector of the Southern Ocean (ASSO). Humpback whale song was detected at nine recording positions in five years. Most songs were recorded in May, austral fall, coinciding with the rapid increase in sea ice concentration at most recording positions. The spatio-temporal pattern in humpback whale singing activity on Southern Ocean feeding grounds is most likely shaped by local prey availability and humpback whale migratory strategies. Furthermore, the comparative analyses of song structures clearly show a differentiation of two song groups, of which one was solely recorded at the western edge of the ASSO and the other song group was recorded throughout the ASSO. This new finding suggests a common feeding ground occupation by multiple humpback whale populations in the ASSO, allowing for cultural and potentially even genetic exchange among populations.

Evidence of Long-Distance Coastal Sea Migration of Atlantic Salmon, Salmo Salar, Smolts from Northwest England (River Derwent).

Combining data from multiple acoustic telemetry studies has revealed that west coast England Atlantic salmon (Salmo salar L.) smolts use a northward migration pathway through the Irish Sea to reach their feeding grounds. 100 Atlantic salmon smolts were tagged in May 2020 in the River Derwent, northwest England as part of an Environment Agency/Natural England funded project. Three tagged smolts were detected on marine acoustic receivers distributed across two separate arrays from different projects in the Irish Sea. One fish had migrated approximately 262km in 10 days from the river mouth at Workington Harbour, Cumbria to the northernmost receiver array operated by the SeaMonitor project; this is the longest tracked marine migration of an Atlantic salmon smolt migrating from United Kingdom. This migrating fish displayed behaviours which resulted in fast northward migration. The remaining two fish were detected on a receiver array operated by a third project: “COMPASS”. These detections further provide evidence that migration to reach marine feeding grounds of salmon smolts from rivers draining into the Irish Sea is northerly. The pattern of these detections would not have been possible without the collaborative efforts of three distinct and separately funded projects to share data. Further work is required to fully understand migration trajectories in this species on the west coast of the British Isles.

Do Gray Whales Count Calories? Comparing Energetic Values of Gray Whale Prey Across Two Different Feeding Grounds in the Eastern North Pacific

Predators must consume enough prey to support costly events, such as reproduction. Meeting high energetic requirements is particularly challenging for migrating baleen whales as their feeding seasons are typically restricted to a limited temporal window and marine prey are notoriously patchy. We assessed the energetic value of the six most common nearshore zooplankton species collected within the Oregon, United States range of the Pacific Coast Feeding Group (PCFG) gray whale (Eschrichtius robustus) feeding grounds, and compared these results to the energetic value of the predominant amphipod species fed on by Eastern North Pacific (ENP) gray whales in the Arctic. Energetic values of Oregon zooplankton differed significantly between species (Kruskal–Wallis χ2 = 123.38, df = 5, p < 0.0001), with Dungeness crab (Cancer magister) megalopae displaying the highest mean caloric content of all tested species (4.21 ± 1.27 kJ g– 1). This value, as well as the mean energetic value of the mysid Neomysis rayii (2.42 ± 1.06 kJ g– 1), are higher than the mean caloric content of Ampelisca macrocephala, the predominant Arctic amphipod. Extrapolations of these results to daily energetic requirements of gray whales indicate that lactating and pregnant gray whales feeding in the PCFG range would require between 0.7–1.03 and 0.22–0.33 metric tons of prey less per day if they fed on Dungeness crab megalopae or N. rayii, respectively, than a whale feeding on A. macrocephala in the Arctic. Yet, these results do not account for differences in availability of these prey species to foraging gray whales. We therefore suggest that other factors, such as prey density, energetic costs of feeding, or natal philopatry and foraging site fidelity play a role in the differences in population sizes between the PCFG and ENP gray whales. Climate change is implicated in causing reduced body condition and increased mortality of both PCFG and ENP gray whales due to decreased prey availability and abundance. Therefore, improved understanding of prey dynamics in response to environmental variability in both regions is critical.

Freshwater biodiversity in western Nepal: A review

Western Nepal is known for its rich freshwater resources that support diverse flora and fauna. Freshwater ecosystems of western Nepal provide multitudes of ecosystem goods, services (irrigation, hydroelectricity, drinking water) to humans, and provide breeding and feeding grounds for many wetland-dependent flora and fauna. But these wetlands are under tremendous pressure mainly due to anthropogenic activities. In this review, we provide a brief overview of the freshwater biodiversity, distributions of wetlands and their status in western Nepal. From this review, we found that western Nepal is rich in freshwater resources and supports diverse flora and fauna. The biologically significant Karnali River is the home of a globally endangered species, the South Asian river dolphin. We also discuss the conservation history of wetlands, identify the gaps, and further suggest priority hotspots for the formulation of future conservation strategies for these ecosystems.

Migratory connections among breeding grounds off the Eastern Pacific and feeding areas in the Antarctic Peninsula based on genotype matching

We analysed 114 DNA samples collected in different locations within the stock G breeding grounds, including Ecuador and the northern and southern Pacific of Colombia. We genotyped 15 microsatellite loci, sexed all samples, and performed genotype comparisons. Genotype comparisons were done using a DNA register of previously genotyped individuals from the Colombian breeding ground and the Antarctic Peninsula feeding Area. We confirmed connectivity between feeding grounds in Antarctic Peninsula and breeding grounds in Colombia and Ecuador using microsatellite loci. We found recaptures within each sampling location in the same year, but we also found a few recaptures in the same locations between years both in breeding and feeding grounds. Interestingly, we found recaptures between breeding and feeding grounds using samples collected 20 years apart, providing some information about longevity in this stock. Further comparisons with other data sets (Brazil, North Pacific) are needed to understand the migratory connectivity of this stock.

Distance Estimation in Reproduction Tasks in a Harbor Seal (Phoca vitulina)

Harbor seals commute between haul-out places and feeding grounds close to the shore or in the open ocean, which is considered a low structured environment, at first sight not providing many cues for orientation/navigation. Nevertheless, seals are well-oriented. For returning to a specific location, seals may use both external and internal cues to, for example, perform path integration requiring the integration of distances traveled and angles steered. We herein assessed the seal’s ability to estimate distances, previously swum or unknown, in reproduction tasks. Reproduction tasks refer to an experimental paradigm in which the experimental animal is required to swim a specific distance first and subsequently reproduce this distance, with visual cues present or absent. The seal was able to estimate and then reproduce distances (0.5–18.5 m) with the smallest error below 10% of the actual distance, and its precision was higher with distances repeatedly swum compared to its performance with unfamiliar distances. In the absence of visual cues, the seal’s performance slightly dropped; however, it was still able to perform the task with an error of 21%. In conclusion, distance estimation may help seals to navigate precisely towards their goals, even if, for example, visual information is not available.

Evaluation of the Dietary Composition of Eurasian Perch (Perca Fluviatilis) in an Interconnected River-lake-gulf Aquatic System as a Supplementary Tool for the Interpretation of Measured Mercury (Hg) Concentrations (One-Year Study).

BackgroundEurasian Perch (Perca fluviatilis) is one of ecologically significant fish species in the Baltic Sea and has been recognized as a suitable organism to measure concentrations of hazardous substances that characterize levels of local pollution (e.g. heavy metals or persistent organic pollutants). However, the ability of the species to inhabit a wide range of feeding grounds raises concerns about the adequacy of monitoring data in relation to the representativeness of measured levels of hazardous substances at specific locations. Accounting of the migratory characteristics of this species can shed light on the origin of the analyzed specimens and thus trace the pollution uptake chain. Perch samples and potential perch prey were collected at three remote stations in a fully interlinked system river– lake–coastal waters of the Gulf of Riga. Mercury (Hg) concentration and stable isotope ratios (13C/12C and 15N/14N) were measured in each sampled item. The perch data were divided into three subgroups associated with specific feeding grounds and one mixed group. A Bayesian mixing model was implemented to quantify the feeding preferences of each group, and based on the results, influence of each food source on Hg uptake by perch was modelled by means of Gaussian GAM model.ResultsCalculated stable isotope ratios of δ13C and δ15N demonstrated clear evidence that perch specimens migrate between the sampling stations. Substantial proportion of specimens sampled in river and lake stations had isotopic signals consistent with feeding in the gulf. The group of perch associated with feeding in river grounds exhibited the highest Hg concentrations with mean value of 209 µg kg-1 wet weight. The food item C. harengus membras and Crustacea showed significant mitigating effect on Hg concentration. The rest of the food items were not significant at the α = 0.05 level, although had different directions of the influence and slope values.ConclusionsThe study clearly showed that the high mobility of perch along associated aquatic systems has noticeable effect. Therefore, trophic position and isotopic signatures, along with identification of the food sources, can serve as important supplementary tools for more accurate data interpretation of Hg accumulation.