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Topic Groups

Synthesis Science-Informed Management of Vulnerable Bycatch in Pelagic Fisheries (Pelagics Topic Group) – Second Year


Milani Chaloupka, (University of Queensland, Australia) Hanna Fennell, (Heriot-Watt University, UK), Eric Gilman (Hawaii Pacific University, USA ), , Martin Hall (Inter-American Tropical Tuna Commission), Antonello Sala (Italian National Research Council -CNR), Liming Song (Shanghai Ocean University, China )

Agenda 20 April 2021 Pelagics Topic Group

Terms of Reference

  1. Assemble a database and conduct a global meta-analysis of existing estimates of the relative risk of capture on different bait types in pelagic longline fisheries. Different species and sizes of pelagic marine predators have different prey, and hence bait, preferences. Managing bait type offers one tool to control species selectivity, including to mitigate vulnerable bycatch. The database will be open source, making it efficient to conduct updated meta-analyses as new records accumulate.

  2. Identify priority research questions that could be addressed through meta-synthesis approaches of relevance to the ICES-FAO WGFTFB. Through a collaborative research prioritisation process, conduct a survey of WGFTFB members and other relevant stakeholders to identify a tentative list of hypotheses suitable for testing by meta-synthesis approaches related to mitigating vulnerable bycatch and mortality risk in pelagic fisheries of relevance to the ICES-FAO WGFTFB.


The purpose of the topic group is to assemble open-source databases to support fisheries synthesis science, including meta-analyses, of bycatch mitigation of vulnerable species in pelagic fisheries.

Overexploitation, including from fishing mortality, is the primary cause of recent marine species extinctions and can cause protracted or irreparable harm and permanent loss of populations, with consequences across manifestations of biodiversity and ecosystem services, including fishery yields. Fisheries that target relatively fecund species, such as tunas, can have profound impacts on incidentally caught or bycatch species that, due to their lower reproduction rates, slow growth, late maturity and other life history traits, are relatively vulnerable to anthropogenic mortalities. Their populations can decline quickly and have limited recovery potential once depleted.

The relative certainty of species-specific catch and survival rate responses to bycatch mitigation method can be categorized into tiers of on an evidence hierarchy. Ideally, decisions should be based on evidence from syntheses of accumulated research, which estimate an overall or pooled effect, and if effects vary across studies, can identify reasons for between-study heterogeneity. Synthesis research also identifies knowledge gaps, and conversely identifies areas where additional studies are not needed, to guide priorities for future research. This requires that researchers have compiled and synthesized (combined) the results from the multiple studies that have already been completed. Quantitative meta-analytic modelling provides the strongest and most generalizable evidence, followed by qualitative systematic literature reviews, then qualitative unstructured literature reviews, and finally by individual studies.

But there is a risk that the results from that single study is context-specific. Results may be affected by the specific conditions, such as the study area, study period, species involved and environmental conditions that prevent the results from that single study from being applicable under different conditions, which is why it is common to have conflicting findings from different individual studies. This is why the validity of a hypothesis cannot be determined from a single study. Furthermore, a single study may have low power and fail to find a meaningful result due to too small a sample size. Meta-syntheses, such as meta-analyses analyze pooled estimates from multiple studies addressing the same question. Due to the larger sample size plus the number of independent studies, correctly designed meta-analytic assessments can provide estimates with increased accuracy over estimates from single studies, with increased statistical power to detect a real effect. By synthesizing estimates from a mixture of independent, small and context-specific studies, the overall estimated effect from meta-analyses is generalizable and relevant over diverse setting.

Passive fishing gears (Passive) – Second year


Peter Ljungberg (Sweden, ), Isabella Kratzer (Germany), and Lotte Kindt-Larsen (Denmark,)

A WGFTFB Topic group convened by Peter Ljungberg, Isabella Kratzer, and Lotte Kindt-Larsen was formed in 2019 on passive gears and will continue the work to 2021.

Terms of Reference

  1. Summarize current and past work in relation to fish pot and trap development, plus gillnet and longline modifications in order to avoid bycatch of protected species (hereunder marine mammals, sea birds and sea turtles).
  2. Discuss and describe methods and their limitations, hereunder catch efficiency and depredations risks. Furthermore compare newly developed bycatch mitigation efforts and their efficiency to standard gear and compare different types of passive gears (e.g. gillnets vs. fish pots/traps) and the processes of depredation.
  3. Identify and make recommendations on how to improve passive gears including unwanted bycatch, high variability in catches and mitigation of depredation from different predators.
  4. Identify potential synergies in developing new approaches to promote sustainability (economically and ecologically) of passive gears.


Passive fishing gears such as gillnets, longlines, traps and pots, belong to the most common fishing methods worldwide. These methods have naturally advantages like efficiency, simple use and size selectiveness. Nevertheless, they have been criticized due to bycatches of higher taxa like sea turtles, sea birds and marine mammals, ghost fishing and their vulnerability to depredation by marine mammals.
In recent years, a lot of effort has been put into the optimization of fish traps and pots, mainly due to gillnet-raiding seals and studies on how to mitigate bycatch in gillnet and longline fisheries have been carried out with differing success, but a scientifically proven management tool or technical solution working across taxa has yet to be developed.
The “Passive” topic group will thus aim to investigate selectivity, efficiency and sturdiness of passive gears, such as gillnets and longlines (mainly species selectivity), fish pots and large-scale fish traps (mainly efficiency and sturdiness). It will document and evaluate current and past work regarding gillnet and longline modifications as well as fish pot and fish trap development. This will include a wide range of fields such as species behaviour, gear design and hydroacoustics. Ongoing and future projects regarding enhanced economical, ecological and social sustainability of passive gears will be discussed and potential synergies identified that will hopefully stimulate new ideas and innovation.

Evaluating the application of artificial light for bycatch mitigation (Light) – Third year


Noëlle Yochum (USA), and Junita Karlsen (Denmark)

A WGFTFB Topic Group convened by Noëlle Yochum and Junita Karlsen was formed at the 2018 meeting in Hirtshals Denmark, to evaluate the application of light as a mechanism for bycatch mitigation. At the 2019, ICES-FAO WGFTFB meeting the ‘Light’ Topic Group of experts the group meet for the second year and the final year for the Topic Group is planned to be 2021.

Terms of Reference

  1. Describe and summarize completed and ongoing research, successes and ‘failures’, related to the ap-plication of light for bycatch mitigation.
  2. Identify patterns with respect to species and fishery/ gear types, noting fish behaviour in response to light (attraction, repulsion, guidance), and other variables that play a role in the efficacy of using artificial light for bycatch mitigation (e.g. vision, depth, etc.).
  3. Describe best sampling techniques for testing the application of artificial light under varying circumstances, including guidance for dealing with common experimental challenges.
  4. Highlight areas of needed research in the field of fish behaviour with respect to light, and fisheries that might benefit from the application of artificial light.


Essential to the study of fishing gear design and use is fish behaviour. The success of bycatch mitigation is linked with understanding how fish interact with fishing gear and respond to the micro-environment in and around the gear. A component of fish behaviour that is increasingly being evaluated is the reaction of fish to artificial light. To that end, from 2012-2014, Heui-Chun An, Mike Breen, Odd-Børre Humborstad, and Yoshkiki Matsushita convened a WGFTFB Topic Group (TG) titled “Use of Artificial Light in Fishing”. The focus of this TG was to evaluate the use of artificial light to affect fish behaviour and stimulate catch, and to research and synthesize information on fish vision and behaviour with respect to light. They also summarized the use of artificial light in fisheries globally and regionally.
The aim of the 2018-2021 'Light' TG is to build on the foundation that has been laid, and to focus on the use of artificial light to enhance bycatch mitigation (e.g. illuminating escape ports or the footrope in trawl gear). Specifically, this TG will focus on creating a community of researchers using light as a fisheries selectivity tool, will develop resources to support this community, and will aggregate and synthesize information from global projects.
Through collective review of this research, we will identify variables that play a role in the efficacy of using artificial light for bycatch mitigation (e.g. species, gear type, fish behaviour). We will also discuss common experimental, technological, and analytical challenges when doing this research, and identify gaps in knowledge and other fisheries that might benefit from the application of artificial light.
Through the analysis of completed and on-going research, and collective knowledge of the TG experts, we will also consider guidelines for conducting research on the application of artificial light for bycatch mitigation. We hope that these meetings will also foster an exchange of ideas and support, and stimulate innovation.