An investigation of stranded dolphins from Xiamen Bay revealed that the Indo-Pacific humpback dolphin (Sousa chinensis) accumulates a variety of heavy metals (HMs) at concentrations that may pose a risk to their health. Foodborne ingestion is considered the major exposure route of marine mammals to environmental contaminants. The health risks of pollutant exposure are of increasing concern in marine mammals due to their large daily intake of food. However, prey fish trophic level and biomagnification trends have not been assessed, thus preventing a comprehensive analysis of HM pollution in food webs. Herein, we assessed the potential risk of HMs to S. chinensis by determining the concentrations of 11 HMs in 10 fish species (180 samples) representing the major prey species of dolphins in the waters of Xiamen Bay. The results of the study showed that zinc (Zn) and arsenic (As) were the most abundant metals in all prey fish, with Zn ranging from 3,812 ng/g ww in Mugil sp. to 7,939 ng/g in Coilia sp., and As ranging from 983 ng/g ww in Setipinna taty to 8,812 ng/g in Cynoglossus sp. The trophic levels of the prey fish were relatively high (from 4 to 5), and methylmercury (MeHg), Zn, cadmium (Cd), and chronium (Cr) exhibited biomagnification, indicating that S. chinensis has a relatively high potential to accumulate HMs. Thus, the risk assessment results indicated that As, selenium (Se), and MeHg may pose a threat to S. chinensis. The method established in this study will facilitate the monitoring of HM-associated health hazards in Indo-Pacific humpback dolphins.

This study describes the social network of a captive group of six adult female and one adult male South African fur seals (Arctocephalus pusillus pusillus), observed on two days one month apart (23 December 2023 and 24 February 2024). Since the fur seals shared their enclosure with two adult male California sea lions (Zalophus californianus), a third observation (April 2024) focused on the mixed-species group. This resident otariid group was housed at the Faunia Madrid zoological facility in Madrid, Spain. A single observer recorded social behaviors using focal sampling with continuous recording for 65 minutes on 23 December, 70 minutes on 24 February, and 65 minutes on 24 April. Each fur seal was observed for a total of 200 minutes, while each sea lion was observed for 65 minutes. Additionally, three scans per session (pre-, mid-, post-observation) yielded 37, 42, and 39 scans, respectively, totaling 118 for fur seals and 39 for sea lions, allowing an assessment of space use in relation to access to valuable resources such as food. The results revealed stable interactive social networks for the most common affiliative behaviors (crossing swimming, rubbing, and synchronized swimming) in fur seals; no aggressive interactions were observed. Within the mixed-species group, two distinct subgroups emerged: one composed of the three oldest females and the adult offspring of two of them, and another consisting of the most recently introduced female along with the two male California sea lions. Sociograms generated allowed for the identification of both the most and least central individuals. Areas with greater resource availability were preferentially used by the animals compared to areas with fewer resources. Additionally, the animals that exhibited more frequency of use in the area with the greatest resource access were South African fur seals and California sea lions, and these animals also had the highest centrality values.

Stable isotope analysis (SIA) is a useful tool to assess the health and foraging habits of large marine predators, metabolic stress, pregnancy, and migration patterns. This study provides baseline SIA data for four Gulf of Maine mysticete species and serves as a benchmark for future assessments. SIA was conducted on skin biopsies collected in two time periods: 1988 to 1992 (n = 15) and 1999 to 2005 (n = 187). Samples were collected from humpback whales (Megaptera novaeangliae; n = 116), fin whales (Balaenoptera physalus; n = 74), minke whales (Balaenoptera acutorostrata; n = 6), and North Atlantic right whales (Eubalaena glacialis; n = 6). There were statistically significant differences in isotopic value among species, years, and regions sampled. By species, North Atlantic right whale δ13C and δ15N levels were significantly different than the other species analyzed. Additionally, humpback whales had a δ15N value that was significantly higher than the value found in fin whales. By date, humpback whales showed significant difference in δ13C in 2002 from the two previous years. For fin whales, 2002 showed significant difference in δ13C for all other years’ samples (2000 to 2003). By region, two regions that were the greatest distance apart (Bay of Fundy and Great South Channel) showed significant differences in δ13C for humpback whales. Demographic analyses for humpback and fin whales found a significant difference between calves versus other age classes, presumably due to nursing. A decadal comparison of humpback whales at one site (Stellwagen Bank) found no significant difference between decades. This dataset provides a benchmark for stable isotope measurements in large baleen whales for this regional ecosystem.

We created an agent-based model (ABM; a computational model) for human–whale interactions in the North Atlantic area. We specifically looked at boats, lobster lines, and rogue fishnet interactions with the North Atlantic right whales (Eubalaena glacialis), and we assessed the conditions under which such interactions are more likely to result in injuries and fatalities for this critically endangered whale, such as the density of ships in the water. ABMs are a methodology particularly useful in data poor problems (where machine learning cannot be used), and are based on rules of interactions between various agents (human and nonhuman) and/or a specific physical environment; they can showcase and assess potential future scenarios. We informed our model with current data from the North Atlantic Right Whale Consortium and the National Oceanic and Atmospheric Administration and present our preliminary findings here.