Journal article
Collateral fishing mortality of Guiana dolphins, Sotalia guianensis at a World Heritage Site in southern Brazil
Biological conservation, Vol.320, pp.1-12
08/2026
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Abstract
Fishing mortality is a key threat to populations of small cetaceans globally, yet comprehensive spatio-temporal assessments of patterns remain limited, particularly in biodiversity hotspots. This study analysed eight years (2016–2023) of stranding data for Guiana dolphins, Sotalia guianensis, along the Paraná coast (88.9 km), southern Brazil, including at an UNESCO World Heritage Site and an Important Marine Mammal Area, supporting the species' largest known resident population (~1800 individuals). From 635 recorded strandings (mean ± SE of 79.3 ± 6.2 year−1), 377 individuals (59.4%) were necropsied to assess fisheries interactions, mortality causes, and population demographics. Kernel density analysis (1 km radius) applied to the raw stranding locations revealed hotspots near major fishing grounds. Strandings also varied seasonally, with peaks during spring and winter and coinciding with onshore winds and larger swells. Evidence of fisheries interactions was detected in 157 dolphins (41.6%), predominantly as impressions, abrasions, and entanglement marks. Among necropsied specimens with a determined cause of death (n = 153), 59.5% were attributed to anthropogenic factors, including drowning from net entanglement. Respiratory lesions indicative of asphyxiation were observed in 49.0% of examined individuals. The log odds of detecting fisheries interactions was 19.5× higher among carcasses in early (total of 121 assessed specimens) than advanced decomposition (166 assessed), suggesting underestimated impacts. The sex ratio was variable but mostly male-biased (1.7:1), with juveniles and adults similarly represented, although the mean ages of the latter (14.2 ± 0.71 years) were younger than the mean midpoint between sexual maturity and L-infinity (~18–22 years), implying a declining population. Annual strandings represented ~5% of the regional population and, considering that strandings typically reflect only ~20% of actual at-sea mortalities, the current fishing mortality likely exceeds sustainable levels for this threatened population. The data emphasise an urgent need for mitigation strategies.
Details
- Title
- Collateral fishing mortality of Guiana dolphins, Sotalia guianensis at a World Heritage Site in southern Brazil
- Creators
- Rafaela V. Guidio - Universidade Federal do ParanáMatt K. Broadhurst - NSW Department of Primary Industries and Regional Development (Australia, Coffs Harbour)João B. Gusmão - Universidade Federal do ParanáCamila Domit - Universidade Federal do Paraná
- Publication Details
- Biological conservation, Vol.320, pp.1-12
- Publisher
- Elsevier Ltd; London
- Grant note
- Programa de Monitoramento de Praias do Laboratorio de Ecologia e Conservacao - PROMAR/UFPR: 316593/20235-0 Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq): 316593/20235-0
We thank all those involved in Projeto de Monitoramento de Praias da Bacia de Santos (PMP-BS) - an environmental constraint legislated by the Brazilian Institute of Environment (IBAMA) for oil and natural gas production and transport by PETROBRAS-ABIO number 640/2015 (3a renewal). JBG thanks the Programa de Monitoramento de Praias do Laboratorio de Ecologia e Conservacao - PROMAR/UFPR for the postdoctorate scholarship. JBG and CD thank the Fundacao da Universidade Federal do Parana para o Desenvolvimento da Ciencia Tecnologia e da Cultura (FUNPAR). CD is a research fellow of the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), grant number 316593/20235-0.
- Identifiers
- 991013380246302368
- Copyright
- © 2026 The Authors.
- Academic Unit
- Faculty of Science and Engineering; National Marine Science Centre
- Language
- English
- Resource Type
- Journal article