ESR 53:509-522 (2024) - DOI: https://doi.org/10.3354/esr01310
From the sky and on the beaches: complementary tools to evaluate common dolphin bycatch in the Bay of Biscay
Hélène Peltier1,*, Sophie Laran1, Willy Dabin1, Pierre Daniel2, Cécile Dars1, Fabien Demaret1, Ghislain Doremus1, Mathieu Genu1, Eléonore Meheust1, Jérôme Spitz1,3, Olivier Van Canneyt1, Vincent Ridoux1,3
ABSTRACT: Since 1989, multiple stranding events of common dolphins have been regularly recorded along the French Atlantic coast. Examination of the carcasses revealed that most animals presented evidence of bycatch. Using stranding data to infer bycatch levels reveals the highest levels of bycatch to have been recorded since 2016 (4000 to 9000 bycaught individuals). This approach is directly influenced by drift conditions, which can greatly contribute to or hinder our ability to estimate bycatch at sea. In the winter of 2021/2022, the French stranding network recorded an unusually high number of strandings until mid-February and few records in March. Investigation of drift conditions revealed low probability of stranding in March due to constant east-west winds. Reverse drift modelling of carcasses stranded in January and February resulted in an estimate of 3670 (95% CI [2750; 5170]) bycaught common dolphins. Dedicated aerial surveys were conducted in the same area during this period, designed to assess abundance and distribution of marine megafauna in French waters. A high number of carcasses of small Delphininae were observed in March 2021, and the number of carcasses floating at sea could be estimated using conventional distance sampling methodology. In March 2021, mortality at sea was thus estimated at 3250 (95% CI [1288;10198]) common dolphins. The complementary use of both methodologies resulted in an estimate of 6920 (95%CI [4038;15368]) bycaught individuals during winter 2021/2022. This case study highlights that a decrease in strandings does not imply a decrease in mortality at sea. Trends in strandings need to be considered in the light of scientific evidence to avoid delays in decision making.
KEY WORDS: Bycatch · Common dolphins · Bay of Biscay · Strandings · Aerial survey · Conventional distance sampling
Full text in pdf format  Supplementary material | Cite this article as: Peltier H, Laran S, Dabin W, Daniel P and others (2024) From the sky and on the beaches: complementary tools to evaluate common dolphin bycatch in the Bay of Biscay. Endang Species Res 53:509-522. https://doi.org/10.3354/esr01310
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