Abstract
Franciscana dolphins (Pontoporia blainvillei) are small odontocete cetaceans that inhabit the coastal waters of Brazil, Uruguay, and Argentina.1,2 They are considered the most endangered cetacean in the southwestern Atlantic.3 Phylogeographic analyses based on genetic structure divided this species into four management areas (FMAI, II, III, and IV). Entanglement in gillnets is currently considered the main threat to this species; however, other anthropogenic impacts (e.g., habitat loss and degradation, chemical and noise pollution), and infectious diseases (e.g., herpesvirus, Brucella sp.), could also play a role.4,5,6
According to data collected during daily beach monitoring executed by Projeto de Monitoramento de Praias, Bacia de Santos (PMP-BS), 837 Franciscana dolphins stranded in São Paulo state (FMA IIb, Brazil) between January 2019 and June 2022: 177 calves, 198 juveniles, 229 adults, and 233 undetermined.7 The stranding events were registered mainly during austral spring–summer (604/837, 72.9%), including 93% of the calves’ reports, which coincides with the birthing season for this species. The central region of the São Paulo coast (Baixada Santista), near the biggest port complex of Latin America, can be considered a stranding hot spot, as over 60% (505/837) of the events were registered there. When comparing annually, an increasing stranding rate has been observed, with 168 reports in 2019, 270 in 2020, and 295 in 2021.
To help better understand the causes of death for these stranded individuals, standardized necropsies were performed on all carcasses in fresh or moderate decomposition status (n=198), including six live stranded individuals that died within 24 hours in care. Gross examination revealed fisheries interactions in 54% (107/198, including 47/62 adults, 42/44 juveniles, and 18/92 calves) of the individuals, with the most likely cause of death being acute asphyxia due to entanglement. These findings reinforce the negative impacts of bycatch in this species, particularly in adults (75.8%) and juveniles (95.4%), although not in calves (19.5%). Preliminary histopathological analysis of the latter indicates that their main lesions are likely associated with maternal filial separation. Hepatic steatosis and fetal distress, as evidenced by meconium and amniotic liquid aspiration and histiocytic pneumonia, were frequently observed, especially in individuals without teeth eruption and <70 cm of total body length.
In 2020, an international consortium, the Alliance for Franciscana Dolphin Conservation Research, Rescue and Rehabilitation (AFCR3), was established by YAQU PACHA, National Marine Mammal Foundation, and Nuremberg Zoo to help address the urgent conservation needs of this species. Through the AFCR3 necropsy working group, we hope to further investigate the potential causes of maternal-filial separation (e.g., mother’s death resulting in calf stranding and rejection at birth). Our aim is for this work to help elaborate and prioritize target conservation strategies to hamper orphaned calf strandings and to increase the survival of rescued individuals under human care in rehabilitation facilities.
Acknowledgments
Projeto de Monitoramento de Praias, Bacia de Santos (PMP-BS) is a project required by the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA) of the Brazilian Ministry of Environment for the environmental licensing process of oil production and transport by Petrobras at the pre-salt province. We thank the funding agencies CNPq (141868/2019-8 and 304999-18), FAPESP (#2016/20956-0, # 2018/25069-7 and 2020/12434-9), and Juan de la Cierva-incorporación (IJC2020-046019-I). We also thank all the members of the Alliance for Franciscana Dolphin Conservation Research, Rescue and Rehabilitation (AFCR3).
*Presenting author
+Student presenter
Literature Cited
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