New ASCOBANS Report on Cetacean Bycatch Monitoring Methods

Bonn, 23 September 2021 – A new report detailing a cost-benefit analysis of bycatch monitoring methods aboard commercial fishing vessels is launched today.  The report is authored by Grant P. Course, and aims to present the methods available, and to aid fisheries to choose the most suitable option for their needs.

Bycatch is considered one of the greatest threats to cetaceans worldwide. Twenty-six species of small cetaceans occur in the ASCOBANS agreement area. Parties to ASCOBANS have passed several resolutions and recommendations aimed at monitoring and reducing bycatch, but the extent of this threat is still unsustainable. EU Regulation 2019/1241 highlights that Member States should collect bycatch data of sensitive species, and that vessels larger than 15m must establish monitoring schemes. However, these vessels fall under only 10% of the European fleet (2019 data). At-sea observer programmes are costly and non-mandatory for vessels <15m length, which make up 90% of the European fleet.

The main issue is that some countries do not routinely monitor or report their bycatch levels. Underreporting leads to large differences between cetacean bycatch estimates depending on the source of the data and the data collection methods.

Accurate and cost-effective methods are required to cover all countries, fishing gears and metiers in the ASCOBANS region. Remote electronic monitoring (REM) systems with CCTV have emerged as an alternative method that could potentially complement traditional monitoring programmes, providing an independent picture of cetacean bycatch and interaction.

The report critically analyses two methods suitable for bycatch monitoring: at-sea observers and REM. In addition, three example fisheries are used to conduct a cost-benefit analysis: A UK gillnet fishery, a French pelagic trawl fishery, and a Danish gillnet fishery.

The suitability of each monitoring method is dependent on the aim of the monitoring process, the levels of coverage required to improve confidence limits and utility, the acceptance of stakeholders towards the selected method, and whether the implementation of the monitoring was mandatory or voluntary.

Overall, according to the study, REM provides a cost-effective and high-quality monitoring coverage especially suited for larger, pelagic vessels or for high levels of fleet coverage. The accuracy of REM is increased with additional fishing sensors, GPS data, and the ongoing development of machine learning approaches that automatically identify bycatch incidents. Developments in portable REM units could allow systems to be swapped across smaller vessels, saving costs. The report highlights the potential to combine REM with a self-reporting system from fishers to report all ETP (endangered, threatened, protected) species bycatch events, and with observers to conduct the video reviews and collect other data.

The report also lists possible recommendations and future developments related to the use of REM as a monitoring tool for ETP (endangered, threatened, protected species) bycatch.

The report was peer reviewed by Al Kingston, Eunice Pinn, Finn Larsen, Gildas Glemarec, Meike Scheidat, and Peter Evans. The report was also consulted with the Joint Bycatch Working Group of ASCOBANS and ACCOBAMS, and will be shared widely.  The Secretariat would like to warmly thank the author, the reviewers, and everyone who contributed to this report – which also launches the ASCOBANS Technical Series.


Grant P. Course (2021). Monitoring Cetacean Bycatch: An Analysis of Different Methods Aboard Commercial Fishing Vessels. ASCOBANS Secretariat, Bonn, Germany. 74 pages. ASCOBANS Technical Series No.1.


Last updated on 06 November 2021

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