Marine Mammal Science最新文献

Maternal grouping dynamics involve trade-offs between: (1) infant protection from predation (predation hypothesis), (2) infant protection from male harassment (infant safety hypothesis), and (3) reducing scramble competition for prey resources (foraging-type scramble competition hypothesis). Using unmanned aerial vehicles, we assessed grouping dynamics in common dolphin (Delphinus delphis) groups containing mother-calf pairs to address these hypotheses. We analyzed social aspects and structural group elements using generalized additive mixed models and modeled group formation using multinomial generalized estimating equations. Calf proportion was higher in very compact groups and in groups of 10–20 individuals but decreased in larger groups. The frequency of socio-sexual behaviors increased in larger groups and decreased in groups with higher calf proportion. Calf distance to its nearest neighbor decreased with increasing group size and cohesion. With a higher proportion of calves, scatter (versus parallel) formation was less frequent. A calf's nearest neighbor was most often (55.4%) a nonmother. Calves showed a preference for being in the front center of the group. These results offer strong support for the predation and infant safety hypotheses and partial support for the foraging-type scramble competition hypothesis. This work provides insight into the adaptive function of maternal strategies in a small delphinid.

Southern sea otters (Enhydra lutris nereis) are a federally listed threatened keystone species of the California kelp forest ecosystem and a sentinel species, indicating environmental health. Mercury (Hg) is a bioaccumulative neurotoxin that poses a threat to high trophic-level species such as marine mammals. We quantified total Hg (THg) concentrations in fur, brain, and liver tissues of necropsied southern sea otters (n = 44) that stranded along the California coast from 2010 to 2019. THg concentrations differed significantly between fur and brain, and between liver and brain. Tissue type explained 64%, and sex explained only 3.3% of overall THg variability (0.48–46.1 μg/g dry weight). All individuals had liver Hg concentrations measuring well under the proposed lower-limit low risk guideline for harp seals, Pagophilus groenlandicus. However, six sea otters exceeded the liver THg moderate risk threshold for terrestrial furbearers to which sea otters are closely related. These data represent baseline THg concentrations in fur, brain, and liver of the southern sea otter and build upon previous studies in various sea otter subspecies. Research on sea otter Hg tolerance and continued monitoring are needed to clarify potential health risks associated with the tissue concentrations observed in this study.

Large whale entanglements are considered a significant threat to populations on a global scale. In the Mexican Pacific and Baja California Peninsula (1996–2021) a total of 218 confirmed entangled whales, from which 99 (45.4%) whales were fully released (66 by the Mexican Whale Disentanglement Network, known as RABEN). Five whale species were reported in confirmed entanglements: humpback (Megaptera novaeangliae, n = 187), gray (Eschrichtius robustus, n = 19), sperm (Physeter macrocephalus, n = 5), Bryde's (Balaenoptera edeni, n = 4), and fin (Balaenoptera physalus, n = 3). Eight types of fishing gear were identified out of 209 different gear sets; gill nets were the most common (n = 101, 48.3%), followed by pots (n = 49, 23.4%). Entanglements were reported in sixteen locations, and Banderas Bay had the most entanglement reports (n = 81, 32.8%). Several entanglements were tracked across multiple locations (n = 7), involving two teams with the most successful releases (n = 5), proving the efficiency of the RABEN entanglement response network. This information can be used to better understand entanglement impacts on large whales in the North Pacific and particularly in Mexico, to work towards mitigation of a problem that affects both whales and fishermen.

In polygynous species, male reproductive success is often determined by their ability to dominate female harems. Harem-holders sire a disproportionate number of offspring. Male dominance tends to correlate with age, but intense competition and early male mortality limit most males from achieving high social status. To maximize reproductive success despite low rank, offspring sex ratio adjustment may have evolved, favoring the sex with higher fitness. If traits influencing dominance are heritable and confer reproductive advantages, we expect fathers with higher reproductive success to produce more sons, as they are more likely to become dominant. In contrast, subordinate males with lower success may benefit from siring more daughters. We tested this hypothesis on a colony of southern elephant seals breeding on the Kerguelen Archipelago. We used genetic markers to link the paternity of 540 pups to 58 breeding males. We found that the probability of siring a son increases from 43% to 54% with paternal relative reproductive success, supporting the offspring sex ratio adjustment hypothesis. Given that various factors influence sex ratio in a population, future studies should tease apart these ecological processes (e.g., paternal dominance, maternal condition, local density, or adult sex ratio) and investigate how they interact with each other.

Estimates of population abundance are required to study the impacts of human activities on populations and assess their conservation status. Despite considerable effort to improve data collection, uncertainty around estimates of cetacean densities can remain large. A fundamental concept underlying distance sampling is the detection function. Here we focus on reducing the uncertainty in the estimation of detection function parameters in analyses combining data sets from multiple surveys, with known effects on the precision of density estimates. We developed detection functions using infinite mixture models that can be applied on data collating multiple species and/or surveys. These models enable automatic clustering by fusing the species and surveys with similar detection functions. We present a simulation analysis of a multisurvey data set in a Bayesian framework where we demonstrated that distance sampling models including fusion effects showed lower uncertainty than classical distance sampling models. We illustrated the benefits of this new model using data of line transect surveys from the Bay of Biscay and Iberian Coast. Future estimates of abundance using conventional distance sampling models on large multispecies surveys or on data sets combining multiple surveys could benefit from this new model to provide more precise density estimates.

The Franz Josef Land population of the Atlantic walrus (Odobenus rosmarus rosmarus) remains one of the least studied. Here, 26 walruses were tagged with satellite-linked radio transmitters in Franz Josef Land archipelago and Victoria Island in summer-autumn 2020 and 2021 to assess movements patterns and area utilization. In addition, 65 grab samples were taken to evaluate macrobenthic foraging resources. The mean duration of data records was 53 ± 27 days. The walruses traveled on average 29 ± 13.5 km/day with a mean speed of 1.2 ± 0.6 km/hr. The travel speed and distance were statistically different for male, female, and immature walruses. The individuals tagged on Victoria Island remained in the vicinity of the island, while walruses tagged within the Franz Josef Land archipelago moved between the islands, utilizing the entire area for foraging trips. One walrus migrated from Franz Josef Land to Novaya Zemlya in late November, providing evidence of connectivity with the Kara-Barents Sea population. The area was characterized by high average biomass of macrobenthos. Bivalve mollusks, Hiatella arctica, were dominating macrobenthic biomass, likely being the main foraging resource for the walruses. Further observations are needed to better understand winter behaviors of Franz Josef Land walruses and possible impacts of climate change on movement patterns.